diff --git a/.env.example b/.env.example
index 2776c8f..e22096c 100644
--- a/.env.example
+++ b/.env.example
@@ -19,3 +19,5 @@ TEST_MODE=false
 POSTGRES_DB=cents
 POSTGRES_USER=cents
 POSTGRES_PASSWORD=change-me
+APP_TIME_ZONE=Asia/Shanghai
+EXCHANGE_RATE_API_URL=https://api.frankfurter.dev
diff --git a/apps/web/src/components/CurrencyPicker.vue b/apps/web/src/components/CurrencyPicker.vue
new file mode 100644
index 0000000..cdd8f7a
--- /dev/null
+++ b/apps/web/src/components/CurrencyPicker.vue
@@ -0,0 +1,83 @@
+<script setup lang="ts">
+import { currencies, type CurrencyCode } from "@cents/domain";
+import { Check, X } from "@lucide/vue";
+
+defineProps<{
+  open: boolean;
+  modelValue: CurrencyCode;
+}>();
+
+const emit = defineEmits<{
+  "update:modelValue": [currency: CurrencyCode];
+  close: [];
+}>();
+
+const commonCurrencies: CurrencyCode[] = ["CNY", "USD", "EUR", "JPY", "THB"];
+const otherCurrencies: CurrencyCode[] = ["HKD"];
+
+function choose(currency: CurrencyCode) {
+  emit("update:modelValue", currency);
+  emit("close");
+}
+</script>
+
+<template>
+  <div v-if="open" class="currency-picker-layer">
+    <button class="currency-picker-scrim" type="button" aria-label="关闭币种选择" @click="emit('close')"></button>
+    <section class="currency-picker-sheet" role="dialog" aria-modal="true" aria-label="选择币种">
+      <div class="currency-picker-handle"></div>
+      <header>
+        <div><strong>选择币种</strong><span>记账金额所使用的币种</span></div>
+        <button type="button" aria-label="关闭" title="关闭" @click="emit('close')"><X :size="19" /></button>
+      </header>
+      <div class="currency-list">
+        <button
+          v-for="code in commonCurrencies"
+          :key="code"
+          type="button"
+          :class="{ selected: modelValue === code }"
+          @click="choose(code)"
+        >
+          <span>{{ currencies[code].symbol }}</span>
+          <strong>{{ currencies[code].name }}<small>{{ code }}</small></strong>
+          <Check v-if="modelValue === code" :size="19" />
+        </button>
+      </div>
+      <p>更多币种</p>
+      <div class="currency-list compact">
+        <button
+          v-for="code in otherCurrencies"
+          :key="code"
+          type="button"
+          :class="{ selected: modelValue === code }"
+          @click="choose(code)"
+        >
+          <span>{{ currencies[code].symbol }}</span>
+          <strong>{{ currencies[code].name }}<small>{{ code }}</small></strong>
+          <Check v-if="modelValue === code" :size="19" />
+        </button>
+      </div>
+    </section>
+  </div>
+</template>
+
+<style scoped>
+.currency-picker-layer { position:absolute; inset:0; z-index:42; }
+.currency-picker-scrim { position:absolute; inset:0; width:100%; height:100%; border:0; background:rgba(18,35,32,.42); backdrop-filter:blur(2px); }
+.currency-picker-sheet { position:absolute; right:0; bottom:0; left:0; max-height:90%; overflow-y:auto; border-radius:14px 14px 0 0; padding:0 16px calc(16px + env(safe-area-inset-bottom)); background:#fff; color:#26342f; box-shadow:0 -16px 36px rgba(22,45,40,.2); }
+.currency-picker-handle { width:38px; height:4px; margin:8px auto 3px; border-radius:2px; background:#b9cac5; }
+.currency-picker-sheet > header { min-height:58px; display:flex; align-items:center; justify-content:space-between; }
+.currency-picker-sheet > header > div { display:grid; gap:1px; }
+.currency-picker-sheet > header strong { font-size:16px; }
+.currency-picker-sheet > header span,.currency-picker-sheet > p { color:#7b8884; font-size:11px; }
+.currency-picker-sheet > header > button { width:36px; height:36px; display:grid; place-items:center; border:0; border-radius:8px; background:#f0f5f3; color:#536762; }
+.currency-picker-sheet > p { margin:13px 2px 7px; }
+.currency-list { display:grid; grid-template-columns:repeat(2,minmax(0,1fr)); gap:7px; }
+.currency-list.compact { grid-template-columns:1fr; }
+.currency-list > button { min-width:0; height:58px; display:grid; grid-template-columns:38px minmax(0,1fr) 20px; align-items:center; gap:9px; border:1px solid #dce7e4; border-radius:8px; padding:7px 10px; background:#fff; color:#344640; text-align:left; }
+.currency-list > button.selected { border-color:#087f72; background:#f0f8f6; color:#087f72; }
+.currency-list > button > span { width:36px; height:36px; display:grid; place-items:center; border-radius:50%; background:#edf3f1; color:#344640; font-size:15px; font-weight:750; }
+.currency-list > button > strong { min-width:0; display:grid; gap:1px; font-size:13px; }
+.currency-list small { color:#82908c; font-size:10px; font-weight:600; }
+@media (max-width:350px) { .currency-list { grid-template-columns:1fr; } }
+</style>
diff --git a/apps/web/src/components/QuickEntryDrawer.vue b/apps/web/src/components/QuickEntryDrawer.vue
index 46ca6d0..beb4ee1 100644
--- a/apps/web/src/components/QuickEntryDrawer.vue
+++ b/apps/web/src/components/QuickEntryDrawer.vue
@@ -1,9 +1,10 @@
 <script setup lang="ts">
-import type { EntryType } from "@cents/domain";
+import { currencies, currencyMinorUnits, type CurrencyCode, type EntryType } from "@cents/domain";
 import { BookOpen, CalendarDays, Check, ChevronDown, Delete as BackspaceIcon, X } from "@lucide/vue";
-import { computed, ref } from "vue";
+import { computed, ref, watch } from "vue";
 import { entryTypes, type Category } from "../data/categories";
 import CategoryCoordinateSelector from "./CategoryCoordinateSelector.vue";
+import CurrencyPicker from "./CurrencyPicker.vue";
 
 type SavedEntry = {
   type: EntryType;
@@ -12,12 +13,14 @@ type SavedEntry = {
   note: string;
   occurredAt: string;
   ledgerIds: string[];
+  currency: CurrencyCode;
 };
 
 const props = defineProps<{
   ledgerId: string;
   ledgerName: string;
   personalLedgerId: string;
+  defaultCurrency: CurrencyCode;
   ledgerOptions: Array<{ id: string; name: string; gradient: string; isPersonal: boolean }>;
 }>();
 
@@ -27,6 +30,7 @@ const emit = defineEmits<{
 }>();
 
 const expression = ref("0");
+const currency = ref<CurrencyCode>(props.defaultCurrency);
 const entryType = ref<EntryType>("expense");
 const categoryPath = ref<Category[]>([]);
 const note = ref("");
@@ -35,6 +39,7 @@ const dateInput = ref<HTMLInputElement | null>(null);
 const selectorOpen = ref(false);
 const noteEditing = ref(false);
 const ledgerPickerOpen = ref(false);
+const currencyPickerOpen = ref(false);
 const selectedLedgerIds = ref([...new Set([props.ledgerId, props.personalLedgerId].filter(Boolean))]);
 
 const typeOption = computed(() => entryTypes.find((item) => item.id === entryType.value)!);
@@ -44,14 +49,16 @@ const categoryPathLabel = computed(() =>
 );
 const categoryDisplayLabel = computed(() => selectedCategory.value?.label ?? typeOption.value.label);
 const calculatedAmount = computed(() => evaluateExpression(expression.value));
+const minorUnits = computed(() => currencyMinorUnits(currency.value));
 const hasCalculation = computed(() => /[+-]/.test(expression.value));
 const calculationLabel = computed(() => expression.value.replaceAll("-", "−").replaceAll("+", " + ").replaceAll("−", " − "));
 const displayAmount = computed(() =>
   new Intl.NumberFormat("zh-CN", {
-    minimumFractionDigits: 2,
-    maximumFractionDigits: 2,
+    minimumFractionDigits: minorUnits.value,
+    maximumFractionDigits: minorUnits.value,
   }).format(calculatedAmount.value),
 );
+const currencySymbol = computed(() => currencies[currency.value].symbol);
 const selectedLedgerLabel = computed(() => {
   const visibleNames = props.ledgerOptions
     .filter((ledger) => !ledger.isPersonal && selectedLedgerIds.value.includes(ledger.id))
@@ -71,10 +78,16 @@ const dateLabel = computed(() => {
   return `${datePart} ${pad(date.getHours())}:${pad(date.getMinutes())}`;
 });
 const canSave = computed(() => {
-  const amount = Math.round(calculatedAmount.value * 100);
+  const amount = Math.round(calculatedAmount.value * 10 ** minorUnits.value);
   return Number.isFinite(amount) && amount > 0 && occurredAtValid.value;
 });
 
+watch(currency, () => {
+  if (minorUnits.value === 0 && expression.value.includes(".")) {
+    expression.value = String(Math.round(calculatedAmount.value));
+  }
+});
+
 function toLocalDateTime(date: Date) {
   const year = date.getFullYear();
   const month = pad(date.getMonth() + 1);
@@ -106,7 +119,8 @@ function evaluateExpression(value: string) {
     if (operand === "" || operand === ".") return;
     const right = Number(operand);
     result = operator === "+" ? result + right : result - right;
-    result = Math.round(result * 100) / 100;
+    const factor = 10 ** minorUnits.value;
+    result = Math.round(result * factor) / factor;
   });
 
   return result;
@@ -119,7 +133,7 @@ function currentOperand() {
 function appendDigit(digit: string) {
   const operand = currentOperand();
   const decimalPlaces = operand.includes(".") ? operand.split(".")[1].length : 0;
-  if (decimalPlaces >= 2 || operand.replace(".", "").length >= 9) return;
+  if ((minorUnits.value > 0 && decimalPlaces >= minorUnits.value) || operand.replace(".", "").length >= 9) return;
 
   if (expression.value === "0") expression.value = digit;
   else if (operand === "0") expression.value = `${expression.value.slice(0, -1)}${digit}`;
@@ -127,6 +141,7 @@ function appendDigit(digit: string) {
 }
 
 function appendDecimal() {
+  if (minorUnits.value === 0) return;
   const operand = currentOperand();
   if (operand.includes(".")) return;
   expression.value += operand === "" ? "0." : ".";
@@ -170,6 +185,12 @@ function openLedgerPicker() {
   ledgerPickerOpen.value = true;
 }
 
+function openCurrencyPicker() {
+  confirmCategory();
+  noteEditing.value = false;
+  currencyPickerOpen.value = true;
+}
+
 function toggleLedger(ledgerId: string) {
   if (ledgerId === props.personalLedgerId) return;
   if (selectedLedgerIds.value.includes(ledgerId)) {
@@ -182,7 +203,7 @@ function toggleLedger(ledgerId: string) {
 }
 
 function saveEntry() {
-  const amount = Math.round(calculatedAmount.value * 100);
+  const amount = Math.round(calculatedAmount.value * 10 ** minorUnits.value);
   if (!canSave.value) return;
 
   emit("save", {
@@ -192,6 +213,7 @@ function saveEntry() {
     note: note.value.trim(),
     occurredAt: new Date(occurredAt.value).toISOString(),
     ledgerIds: selectedLedgerIds.value,
+    currency: currency.value,
   });
 }
 </script>
@@ -205,7 +227,9 @@ function saveEntry() {
     <header class="drawer-header">
       <div class="amount-block">
         <div class="amount-result">
-          <span class="amount-prefix">¥</span>
+          <button class="amount-prefix" type="button" :aria-label="`切换币种，当前${currencies[currency].name}`" @click="openCurrencyPicker">
+            {{ currencySymbol }}
+          </button>
           <strong class="amount-value">{{ displayAmount }}</strong>
         </div>
         <span v-if="hasCalculation" class="calculation-line">{{ calculationLabel }}</span>
@@ -306,4 +330,6 @@ function saveEntry() {
       <button class="quick-ledger-picker-done" type="button" @click="ledgerPickerOpen = false"><Check :size="18" />完成</button>
     </section>
   </div>
+
+  <CurrencyPicker v-model="currency" :open="currencyPickerOpen" @close="currencyPickerOpen = false" />
 </template>
diff --git a/apps/web/src/components/QuickEntryHost.vue b/apps/web/src/components/QuickEntryHost.vue
index a473d23..eb2a354 100644
--- a/apps/web/src/components/QuickEntryHost.vue
+++ b/apps/web/src/components/QuickEntryHost.vue
@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import type { CurrencyCode } from "@cents/domain";
 import { BarChart3, BookOpen, Check, CircleUserRound, LibraryBig, Plus } from "@lucide/vue";
 import { computed, onMounted, ref } from "vue";
 import { useRoute } from "vue-router";
@@ -31,12 +32,12 @@ async function saveEntry(input: {
   note: string;
   occurredAt: string;
   ledgerIds: string[];
+  currency: CurrencyCode;
 }) {
   const ledger = ledgerStore.currentLedger;
   if (!ledger) return;
   await entryStore.addEntry(createEntry({
     ...input,
-    currency: ledger.defaultCurrency,
     createdBy: authStore.user?.id,
   }));
   drawerOpen.value = false;
@@ -65,6 +66,7 @@ async function saveEntry(input: {
       :ledger-name="ledgerStore.currentLedger.name"
       :ledger-options="ledgerOptions"
       :personal-ledger-id="ledgerStore.personalLedger?.id ?? ''"
+      :default-currency="ledgerStore.currentLedger.defaultCurrency"
       @close="drawerOpen = false"
       @save="saveEntry"
     />
diff --git a/apps/web/src/data/db.ts b/apps/web/src/data/db.ts
index 54b03a0..9cb9d81 100644
--- a/apps/web/src/data/db.ts
+++ b/apps/web/src/data/db.ts
@@ -1,5 +1,5 @@
 import Dexie, { type EntityTable } from "dexie";
-import type { LedgerEntry, SyncOperation } from "@cents/domain";
+import type { ConversionStatus, CurrencyCode, LedgerEntry, SyncOperation } from "@cents/domain";
 import type { LedgerRecord, UserPreference } from "./ledgers";
 
 export type SyncMetadata = {
@@ -8,12 +8,23 @@ export type SyncMetadata = {
   updatedAt: string;
 };
 
+export type LocalExchangeRate = {
+  id: string;
+  currency: CurrencyCode;
+  requestedDate: string;
+  effectiveDate: string;
+  cnyPerUnit: string;
+  status: Exclude<ConversionStatus, "pending">;
+  updatedAt: string;
+};
+
 export const db = new Dexie("cents") as Dexie & {
   entries: EntityTable<LedgerEntry, "id">;
   syncOperations: EntityTable<SyncOperation, "id">;
   ledgers: EntityTable<LedgerRecord, "id">;
   userPreferences: EntityTable<UserPreference, "id">;
   syncMetadata: EntityTable<SyncMetadata, "id">;
+  exchangeRates: EntityTable<LocalExchangeRate, "id">;
 };
 
 db.version(1).stores({
@@ -63,3 +74,42 @@ db.version(4).stores({
     delete operation.ledgerId;
   });
 });
+
+db.version(5).stores({
+  entries: "id, ownerId, *ledgerIds, occurredAt, updatedAt, deletedAt, conversionStatus",
+  syncOperations: "id, *ledgerIds, createdAt, syncedAt",
+  ledgers: "id, updatedAt, archivedAt",
+  userPreferences: "id, userId, key, updatedAt",
+  syncMetadata: "id, updatedAt",
+  exchangeRates: "id, currency, requestedDate, updatedAt",
+}).upgrade(async (transaction) => {
+  const normalizeEntry = (entry: LegacyEntry) => {
+    const date = localDate(entry.occurredAt);
+    entry.exchangeRateDate ??= date;
+    if (entry.currency === "CNY") {
+      entry.baseCurrency = "CNY";
+      entry.baseAmount = entry.amount;
+      entry.exchangeRate = "1";
+      entry.exchangeRateEffectiveDate = date;
+      entry.exchangeRateSource = "system";
+      entry.conversionStatus = "exact";
+    } else if (!entry.conversionStatus || (entry.exchangeRate === "1" && entry.exchangeRateSource === "manual")) {
+      entry.baseCurrency = "CNY";
+      entry.baseAmount = null;
+      entry.exchangeRate = null;
+      entry.exchangeRateEffectiveDate = null;
+      entry.exchangeRateSource = "system";
+      entry.conversionStatus = "pending";
+    }
+  };
+  await transaction.table<LegacyEntry>("entries").toCollection().modify(normalizeEntry);
+  await transaction.table<LegacyOperation>("syncOperations").toCollection().modify((operation) => {
+    normalizeEntry(operation.payload);
+  });
+});
+
+function localDate(value: string) {
+  const date = new Date(value);
+  const pad = (part: number) => String(part).padStart(2, "0");
+  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`;
+}
diff --git a/apps/web/src/data/entries.ts b/apps/web/src/data/entries.ts
index 3eb5b52..dbac951 100644
--- a/apps/web/src/data/entries.ts
+++ b/apps/web/src/data/entries.ts
@@ -16,6 +16,8 @@ const baseCurrency: CurrencyCode = "CNY";
 
 export function createEntry(input: EntryInput): LedgerEntry {
   const now = new Date().toISOString();
+  const exchangeRateDate = localDate(input.occurredAt);
+  const isCny = input.currency === "CNY";
 
   return {
     id: createId(),
@@ -25,9 +27,12 @@ export function createEntry(input: EntryInput): LedgerEntry {
     amount: input.amount,
     currency: input.currency,
     baseCurrency,
-    baseAmount: input.amount,
-    exchangeRate: "1",
-    exchangeRateSource: "manual",
+    baseAmount: isCny ? input.amount : null,
+    exchangeRate: isCny ? "1" : null,
+    exchangeRateDate,
+    exchangeRateEffectiveDate: isCny ? exchangeRateDate : null,
+    exchangeRateSource: "system",
+    conversionStatus: isCny ? "exact" : "pending",
     categoryId: input.categoryId,
     note: input.note,
     occurredAt: input.occurredAt,
@@ -40,6 +45,12 @@ export function createEntry(input: EntryInput): LedgerEntry {
   };
 }
 
+export function localDate(value: string) {
+  const date = new Date(value);
+  const pad = (part: number) => String(part).padStart(2, "0");
+  return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`;
+}
+
 export function createDemoEntries(): LedgerEntry[] {
   const now = new Date();
   const at = (daysAgo: number, hours: number, minutes: number) => {
diff --git a/apps/web/src/stores/entries.ts b/apps/web/src/stores/entries.ts
index 8a0e567..e75ebef 100644
--- a/apps/web/src/stores/entries.ts
+++ b/apps/web/src/stores/entries.ts
@@ -1,7 +1,8 @@
 import { defineStore } from "pinia";
-import type { LedgerEntry, SyncOperation } from "@cents/domain";
+import { calculateCnyAmount, type CurrencyCode, type LedgerEntry, type SyncOperation } from "@cents/domain";
 import { apiRequest } from "../data/api";
 import { db } from "../data/db";
+import { localDate } from "../data/entries";
 import { createId } from "../data/ids";
 import { useAuthStore } from "./auth";
 
@@ -137,6 +138,7 @@ export const useEntryStore = defineStore("entries", {
       });
 
       await this.refreshLocalEntries();
+      void this.resolveLocalConversion(entry.id);
       void this.syncEntries();
     },
     async updateEntry(entry: LedgerEntry) {
@@ -144,10 +146,25 @@ export const useEntryStore = defineStore("entries", {
       const existing = await db.entries.get(entry.id);
       if (!existing || existing.deletedAt) throw new Error("Entry not found");
 
+      const exchangeRateDate = localDate(entry.occurredAt);
+      const conversionChanged = existing.amount !== entry.amount
+        || existing.currency !== entry.currency
+        || existing.exchangeRateDate !== exchangeRateDate;
       const updated: LedgerEntry = {
         ...existing,
         ...entry,
         ledgerIds: [...new Set(entry.ledgerIds)],
+        baseCurrency: "CNY",
+        baseAmount: conversionChanged ? (entry.currency === "CNY" ? entry.amount : null) : existing.baseAmount,
+        exchangeRate: conversionChanged ? (entry.currency === "CNY" ? "1" : null) : existing.exchangeRate,
+        exchangeRateDate,
+        exchangeRateEffectiveDate: conversionChanged
+          ? (entry.currency === "CNY" ? exchangeRateDate : null)
+          : existing.exchangeRateEffectiveDate,
+        exchangeRateSource: conversionChanged ? "system" : existing.exchangeRateSource,
+        conversionStatus: conversionChanged
+          ? (entry.currency === "CNY" ? "exact" : "pending")
+          : existing.conversionStatus,
         updatedAt: new Date().toISOString(),
         updatedBy: auth.user?.id ?? existing.updatedBy,
         version: existing.version + 1,
@@ -170,9 +187,75 @@ export const useEntryStore = defineStore("entries", {
       });
 
       await this.refreshLocalEntries();
+      if (conversionChanged) void this.resolveLocalConversion(updated.id);
       void this.syncEntries();
       return updated;
     },
+    async resolveLocalConversion(entryId: string) {
+      const entry = await db.entries.get(entryId);
+      if (!entry || entry.deletedAt || entry.currency === "CNY") return;
+      const cacheId = `${entry.currency}:${entry.exchangeRateDate}`;
+      let cached = await db.exchangeRates.get(cacheId);
+      if (!cached && (typeof navigator === "undefined" || navigator.onLine)) {
+        try {
+          const result = await apiRequest<{
+            rate: {
+              currency: CurrencyCode;
+              requestedDate: string;
+              effectiveDate: string | null;
+              cnyPerUnit: string | null;
+              status: "exact" | "fallback" | "pending";
+            };
+          }>(`/api/exchange-rates/${entry.currency}/${entry.exchangeRateDate}`);
+          if (result.rate.cnyPerUnit && result.rate.effectiveDate && result.rate.status !== "pending") {
+            cached = {
+              id: cacheId,
+              currency: result.rate.currency,
+              requestedDate: result.rate.requestedDate,
+              effectiveDate: result.rate.effectiveDate,
+              cnyPerUnit: result.rate.cnyPerUnit,
+              status: result.rate.status,
+              updatedAt: new Date().toISOString(),
+            };
+            await db.exchangeRates.put(cached);
+          }
+        } catch {
+          // The original-currency entry is already durable; conversion can retry after sync.
+        }
+      }
+      if (!cached) {
+        const candidates = await db.exchangeRates.where("currency").equals(entry.currency).toArray();
+        cached = candidates
+          .sort((left, right) => {
+            const leftFuture = left.requestedDate > entry.exchangeRateDate;
+            const rightFuture = right.requestedDate > entry.exchangeRateDate;
+            if (leftFuture !== rightFuture) return leftFuture ? 1 : -1;
+            return Math.abs(Date.parse(left.requestedDate) - Date.parse(entry.exchangeRateDate))
+              - Math.abs(Date.parse(right.requestedDate) - Date.parse(entry.exchangeRateDate));
+          })[0];
+      }
+      if (!cached) return;
+
+      const current = await db.entries.get(entryId);
+      if (
+        !current
+        || current.deletedAt
+        || current.amount !== entry.amount
+        || current.currency !== entry.currency
+        || current.exchangeRateDate !== entry.exchangeRateDate
+      ) return;
+      const baseAmount = calculateCnyAmount(current.amount, current.currency, cached.cnyPerUnit);
+      await db.entries.update(entryId, {
+        baseAmount,
+        exchangeRate: cached.cnyPerUnit,
+        exchangeRateEffectiveDate: cached.effectiveDate,
+        exchangeRateSource: "system",
+        conversionStatus: cached.requestedDate === current.exchangeRateDate && cached.status === "exact"
+          ? "exact"
+          : "fallback",
+      });
+      await this.refreshLocalEntries();
+    },
     async deleteEntry(entryId: string) {
       const auth = useAuthStore();
       const existing = await db.entries.get(entryId);
diff --git a/apps/web/src/styles.css b/apps/web/src/styles.css
index 5be3533..7bdfcdb 100644
--- a/apps/web/src/styles.css
+++ b/apps/web/src/styles.css
@@ -744,11 +744,20 @@ input:focus-visible {
 }
 
 .amount-prefix {
+  min-width: 30px;
+  border: 0;
+  border-bottom: 1px dashed #9baba6;
+  padding: 0 2px 1px;
+  background: transparent;
   color: #70807c;
   font-size: 20px;
   font-weight: 650;
+  line-height: 1.1;
 }
 
+.conversion-notice { min-height:38px; display:flex; align-items:center; border-bottom:1px solid #eadfca; padding:7px 12px; background:#fff9ed; color:#775b24; font-size:12px; }
+.conversion-notice span { display:flex; align-items:center; gap:6px; }
+
 .amount-value {
   overflow: hidden;
   color: #172421;
diff --git a/apps/web/src/views/EntryDetailView.vue b/apps/web/src/views/EntryDetailView.vue
index ba686f7..6238323 100644
--- a/apps/web/src/views/EntryDetailView.vue
+++ b/apps/web/src/views/EntryDetailView.vue
@@ -1,5 +1,11 @@
 <script setup lang="ts">
-import type { EntryType, LedgerEntry } from "@cents/domain";
+import {
+  currencies,
+  currencyMinorUnits,
+  type CurrencyCode,
+  type EntryType,
+  type LedgerEntry,
+} from "@cents/domain";
 import {
   ArrowLeft,
   BookOpen,
@@ -25,6 +31,7 @@ import {
 import { ledgerTheme } from "../data/ledgers";
 import { useEntryStore } from "../stores/entries";
 import { useLedgerStore } from "../stores/ledgers";
+import CurrencyPicker from "../components/CurrencyPicker.vue";
 
 type CategorySheetMode = "parent" | "child";
 
@@ -40,8 +47,10 @@ const errorMessage = ref("");
 const categorySheetMode = ref<CategorySheetMode | null>(null);
 const ledgerPickerOpen = ref(false);
 const dateInput = ref<HTMLInputElement | null>(null);
+const currencyPickerOpen = ref(false);
 
 const amount = ref("");
+const currency = ref<CurrencyCode>("CNY");
 const ledgerIds = ref<string[]>([]);
 const parentCategoryId = ref("");
 const childCategoryId = ref("");
@@ -92,6 +101,13 @@ const createdAtLabel = computed(() => {
     hour12: false,
   }).format(new Date(entry.value.createdAt));
 });
+const currencySymbol = computed(() => currencies[currency.value].symbol);
+const conversionLabel = computed(() => {
+  if (!entry.value || entry.value.currency === "CNY") return "";
+  if (entry.value.baseAmount === null) return "人民币金额等待后台换算";
+  const rateDate = entry.value.exchangeRateEffectiveDate ?? entry.value.exchangeRateDate;
+  return `约 ¥${(entry.value.baseAmount / 100).toLocaleString("zh-CN", { minimumFractionDigits: 2, maximumFractionDigits: 2 })} · ${rateDate}${entry.value.conversionStatus === "fallback" ? " 最近汇率" : ""}`;
+});
 
 onMounted(async () => {
   await Promise.all([store.loadEntries(), ledgerStore.loadLedgers()]);
@@ -102,7 +118,9 @@ onMounted(async () => {
 
 function hydrate(value: LedgerEntry) {
   entry.value = value;
-  amount.value = (value.amount / 100).toFixed(2);
+  currency.value = value.currency;
+  const minorUnits = currencyMinorUnits(value.currency);
+  amount.value = (value.amount / 10 ** minorUnits).toFixed(minorUnits);
   ledgerIds.value = [...new Set([...value.ledgerIds, ledgerStore.personalLedger?.id].filter((id): id is string => Boolean(id)))];
   note.value = value.note;
   occurredAt.value = toLocalDateTime(new Date(value.occurredAt));
@@ -166,12 +184,11 @@ async function saveEntry() {
   saving.value = true;
   errorMessage.value = "";
   try {
-    const cents = Math.round(numericAmount * 100);
-    const exchangeRate = Number(entry.value.exchangeRate) || 1;
+    const minorAmount = Math.round(numericAmount * 10 ** currencyMinorUnits(currency.value));
     const updated = await store.updateEntry({
       ...entry.value,
-      amount: cents,
-      baseAmount: Math.round(cents * exchangeRate),
+      amount: minorAmount,
+      currency: currency.value,
       ledgerIds: [...ledgerIds.value],
       categoryId: childCategoryId.value || parentCategoryId.value || entryType.value,
       note: note.value.trim(),
@@ -228,9 +245,12 @@ async function deleteEntry() {
           </div>
           <span class="entry-type-label">{{ typeOption.label }}</span>
           <label class="entry-amount-input">
-            <span>¥</span>
+            <button type="button" :aria-label="`切换币种，当前${currencies[currency].name}`" @click="currencyPickerOpen = true">
+              {{ currencySymbol }}
+            </button>
             <input v-model="amount" inputmode="decimal" aria-label="金额" />
           </label>
+          <span v-if="conversionLabel" class="entry-conversion-label">{{ conversionLabel }}</span>
         </section>
 
         <section class="entry-edit-fields" aria-label="编辑条目">
@@ -361,6 +381,8 @@ async function deleteEntry() {
       </div>
     </Transition>
 
+    <CurrencyPicker v-model="currency" :open="currencyPickerOpen" @close="currencyPickerOpen = false" />
+
     <div v-if="ledgerPickerOpen" class="quick-ledger-picker-layer">
       <button class="quick-ledger-picker-scrim" type="button" aria-label="关闭账本选择" @click="ledgerPickerOpen = false"></button>
       <section class="quick-ledger-picker" aria-label="选择关联账本">
@@ -470,7 +492,13 @@ async function deleteEntry() {
   color: #0d8b67;
 }
 
-.entry-amount-input > span {
+.entry-amount-input > button {
+  min-width: 34px;
+  border: 0;
+  border-bottom: 1px dashed currentColor;
+  padding: 0 2px 1px;
+  background: transparent;
+  color: inherit;
   font-size: 23px;
   font-weight: 700;
 }
@@ -488,6 +516,12 @@ async function deleteEntry() {
   text-align: center;
 }
 
+.entry-conversion-label {
+  min-height: 16px;
+  color: #7b8884;
+  font-size: 11px;
+}
+
 .entry-edit-fields {
   margin-top: 12px;
   border-top: 1px solid #dce7e4;
diff --git a/apps/web/src/views/LedgerSettingsView.vue b/apps/web/src/views/LedgerSettingsView.vue
index 8f280e2..7ed1d79 100644
--- a/apps/web/src/views/LedgerSettingsView.vue
+++ b/apps/web/src/views/LedgerSettingsView.vue
@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import type { LedgerThemeId } from "@cents/domain";
+import type { CurrencyCode, LedgerThemeId } from "@cents/domain";
 import { ArrowLeft, Check } from "@lucide/vue";
 import { onMounted, ref } from "vue";
 import { useRouter } from "vue-router";
@@ -10,7 +10,7 @@ const router = useRouter();
 const ledgerStore = useLedgerStore();
 const name = ref("");
 const themeId = ref<LedgerThemeId>("jade");
-const currency = ref<"CNY" | "USD" | "EUR" | "JPY" | "HKD">("CNY");
+const currency = ref<CurrencyCode>("CNY");
 const saving = ref(false);
 
 onMounted(async () => {
@@ -44,7 +44,7 @@ async function save() {
     <form class="settings-form" @submit.prevent="save">
       <section>
         <label><span>账本名称</span><input v-model="name" maxlength="24" :disabled="ledgerStore.currentLedger?.isPersonal" required /></label>
-        <label><span>默认币种</span><select v-model="currency"><option value="CNY">人民币 CNY</option><option value="USD">美元 USD</option><option value="EUR">欧元 EUR</option><option value="JPY">日元 JPY</option><option value="HKD">港币 HKD</option></select></label>
+        <label><span>默认币种</span><select v-model="currency"><option value="CNY">人民币 CNY</option><option value="USD">美元 USD</option><option value="EUR">欧元 EUR</option><option value="JPY">日元 JPY</option><option value="THB">泰铢 THB</option><option value="HKD">港币 HKD</option></select></label>
       </section>
       <section class="color-setting">
         <span>账本主题</span>
diff --git a/apps/web/src/views/LedgerView.vue b/apps/web/src/views/LedgerView.vue
index 1e5b2b6..d095d0c 100644
--- a/apps/web/src/views/LedgerView.vue
+++ b/apps/web/src/views/LedgerView.vue
@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import type { LedgerEntry } from "@cents/domain";
+import { formatCurrencyAmount, type LedgerEntry } from "@cents/domain";
 import {
   BookOpen,
   ChevronDown,
@@ -7,6 +7,7 @@ import {
   CloudOff,
   Copy,
   LoaderCircle,
+  Clock3,
   MoreHorizontal,
   RefreshCw,
   Search,
@@ -59,6 +60,7 @@ const monthlyEntries = computed(() => {
 const totals = computed(() => {
   return monthlyEntries.value.reduce(
     (result, entry) => {
+      if (entry.baseAmount === null) return result;
       if (entry.type === "income") result.income += entry.baseAmount;
       else result.expense += entry.baseAmount;
       return result;
@@ -73,6 +75,9 @@ const expenseText = computed(() => formatMoney(totals.value.expense));
 const visibleMonthlyEntries = computed(() => monthlyEntries.value.slice(0, visibleCount.value));
 const hasMoreEntries = computed(() => visibleCount.value < monthlyEntries.value.length);
 const pendingEntryCount = computed(() => store.pendingEntryCount(ledgerStore.currentLedgerId));
+const pendingConversionCount = computed(() =>
+  monthlyEntries.value.filter((entry) => entry.conversionStatus === "pending").length,
+);
 const currentTheme = computed(() => ledgerTheme(ledgerStore.currentLedger?.theme));
 
 const dailyTotals = computed(() => {
@@ -80,6 +85,7 @@ const dailyTotals = computed(() => {
   for (const entry of monthlyEntries.value) {
     const key = localDateKey(entry.occurredAt);
     const summary = summaries.get(key) ?? { income: 0, expense: 0 };
+    if (entry.baseAmount === null) continue;
     if (entry.type === "income") summary.income += entry.baseAmount;
     else summary.expense += entry.baseAmount;
     summaries.set(key, summary);
@@ -310,6 +316,9 @@ async function shareLedger() {
           <RefreshCw :size="15" :class="{ spinning: store.syncing }" />{{ store.syncing ? "同步中" : "立即同步" }}
         </button>
       </div>
+      <div v-if="pendingConversionCount" class="conversion-notice" role="status">
+        <span><Clock3 :size="15" />{{ pendingConversionCount }} 条外币账目等待换算</span>
+      </div>
       <div class="list-toolbar">
         <div class="list-toolbar-copy">
           <div class="list-toolbar-heading">
@@ -358,9 +367,13 @@ async function shareLedger() {
           </div>
           <div class="entry-value">
             <strong :class="entry.type">
-              {{ entry.type === "expense" ? "−" : "+" }}{{ formatMoney(entry.baseAmount) }}
+              {{ entry.type === "expense" ? "−" : "+" }}{{ entry.baseAmount === null
+                ? formatCurrencyAmount(entry.amount, entry.currency)
+                : `¥${formatMoney(entry.baseAmount)}` }}
             </strong>
-            <span>{{ formatTime(entry.occurredAt) }}</span>
+            <span>{{ entry.currency === "CNY" || entry.baseAmount === null
+              ? formatTime(entry.occurredAt)
+              : formatCurrencyAmount(entry.amount, entry.currency) }}</span>
           </div>
         </RouterLink>
       </section>
diff --git a/apps/web/src/views/LedgersView.vue b/apps/web/src/views/LedgersView.vue
index 07837bc..8f1923e 100644
--- a/apps/web/src/views/LedgersView.vue
+++ b/apps/web/src/views/LedgersView.vue
@@ -98,7 +98,7 @@ async function createLedger() {
             <button type="button" aria-label="关闭" title="关闭" @click="closeCreate"><X :size="20" /></button>
           </header>
           <label class="create-ledger-name"><span>账本名称</span><input v-model="name" maxlength="40" placeholder="例如：旅行计划" autocomplete="off" autofocus required /></label>
-          <label class="create-ledger-currency"><span>默认币种</span><select v-model="currency"><option value="CNY">人民币 CNY</option><option value="USD">美元 USD</option><option value="EUR">欧元 EUR</option><option value="JPY">日元 JPY</option><option value="HKD">港币 HKD</option></select></label>
+          <label class="create-ledger-currency"><span>默认币种</span><select v-model="currency"><option value="CNY">人民币 CNY</option><option value="USD">美元 USD</option><option value="EUR">欧元 EUR</option><option value="JPY">日元 JPY</option><option value="THB">泰铢 THB</option><option value="HKD">港币 HKD</option></select></label>
           <fieldset class="create-ledger-colors">
             <legend>账本主题</legend>
             <div><button v-for="theme in ledgerThemes" :key="theme.id" type="button" :class="{ active: themeId === theme.id }" :style="{ background: theme.gradient }" :aria-label="`选择${theme.name}主题`" :title="theme.name" @click="themeId = theme.id"><Check v-if="themeId === theme.id" :size="17" /></button></div>
diff --git a/apps/web/src/views/StatsView.vue b/apps/web/src/views/StatsView.vue
index d7b14c6..e566eff 100644
--- a/apps/web/src/views/StatsView.vue
+++ b/apps/web/src/views/StatsView.vue
@@ -71,10 +71,12 @@ const entries = computed(() => {
 });
 
 const totals = computed(() => summarize(entries.value));
+const convertedEntries = computed(() => entries.value.filter((entry) => entry.baseAmount !== null));
+const pendingConversionCount = computed(() => entries.value.length - convertedEntries.value.length);
 
 const dailyStats = computed(() => {
   const groups = new Map<string, LedgerEntry[]>();
-  for (const entry of entries.value) {
+  for (const entry of convertedEntries.value) {
     const date = new Date(entry.occurredAt);
     const key = toDateInput(date);
     groups.set(key, [...(groups.get(key) ?? []), entry]);
@@ -89,9 +91,9 @@ const maxDailyAmount = computed(() =>
 
 const categoryStats = computed(() => {
   const groups = new Map<string, { amount: number; count: number }>();
-  for (const entry of entries.value) {
+  for (const entry of convertedEntries.value) {
     const current = groups.get(entry.categoryId) ?? { amount: 0, count: 0 };
-    current.amount += entry.baseAmount;
+    current.amount += entry.baseAmount!;
     current.count += 1;
     groups.set(entry.categoryId, current);
   }
@@ -106,7 +108,7 @@ const maxCategoryAmount = computed(() => Math.max(1, ...categoryStats.value.map(
 
 const memberStats = computed(() => {
   const groups = new Map<string, LedgerEntry[]>();
-  for (const entry of entries.value) groups.set(entry.createdBy, [...(groups.get(entry.createdBy) ?? []), entry]);
+  for (const entry of convertedEntries.value) groups.set(entry.createdBy, [...(groups.get(entry.createdBy) ?? []), entry]);
   return Array.from(groups, ([userId, items]) => ({
     userId,
     name: ledgerStore.memberName(userId),
@@ -122,6 +124,7 @@ onMounted(async () => {
 function summarize(items: LedgerEntry[]) {
   return items.reduce(
     (result, entry) => {
+      if (entry.baseAmount === null) return result;
       if (entry.type === "income") result.income += entry.baseAmount;
       else result.expense += entry.baseAmount;
       return result;
@@ -193,6 +196,9 @@ function dailyLabel(value: string) {
         <div class="income"><span><TrendingUp :size="17" />收入</span><strong>{{ money(totals.income) }}</strong></div>
         <div class="expense"><span><TrendingDown :size="17" />支出</span><strong>{{ money(totals.expense) }}</strong></div>
       </section>
+      <p v-if="pendingConversionCount" class="stats-conversion-notice">
+        {{ pendingConversionCount }} 条外币账目等待换算，暂未计入人民币统计
+      </p>
 
       <div class="stats-tabs" role="tablist" aria-label="统计维度">
         <button type="button" :class="{ active: activeTab === 'flow' }" @click="activeTab = 'flow'">收支</button>
@@ -269,6 +275,7 @@ function dailyLabel(value: string) {
 .stats-summary .balance strong { font-size:24px; }
 .stats-summary .income { color: #0d8b67; }
 .stats-summary .expense { color: #d84c36; }
+.stats-conversion-notice { margin:8px 0 0; border-left:3px solid #d69a32; padding:7px 9px; background:#fff8e9; color:#755719; font-size:11px; }
 .stats-tabs { display: grid; grid-template-columns: repeat(3,1fr); gap: 4px; margin: 14px 0 10px; border-radius: 8px; padding: 4px; background: #e7eeec; }
 .stats-tabs button { height: 38px; border: 0; border-radius: 6px; background: transparent; color: #71807c; font-size: 13px; font-weight: 680; }
 .stats-tabs button.active { background: #fff; color: #087f72; box-shadow: 0 2px 7px rgba(28,52,47,.12); }
diff --git a/compose.pro.yaml b/compose.pro.yaml
index 64f0a2b..afed19d 100644
--- a/compose.pro.yaml
+++ b/compose.pro.yaml
@@ -25,6 +25,8 @@ services:
       DATABASE_URL: postgres://${POSTGRES_USER:-cents}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB:-cents}
       PUBLIC_ORIGIN: https://${DOMAIN}
       COOKIE_SECURE: "true"
+      APP_TIME_ZONE: ${APP_TIME_ZONE:-Asia/Shanghai}
+      EXCHANGE_RATE_API_URL: ${EXCHANGE_RATE_API_URL:-https://api.frankfurter.dev}
       PORT: "3000"
     depends_on:
       db:
diff --git a/docs/多币种与汇率.md b/docs/多币种与汇率.md
index 08809ec..95ccd17 100644
--- a/docs/多币种与汇率.md
+++ b/docs/多币种与汇率.md
@@ -2,7 +2,7 @@
 
 ## 状态
 
-- 设计状态：待实现。
+- 设计状态：首版已实现，后续按本文验收项继续补齐测试和运营能力。
 - 记账本位币固定为 `CNY`。
 - 本文描述多币种记账、汇率缓存、离线降级及人民币汇总的首版方案。
 
diff --git a/packages/domain/src/index.test.ts b/packages/domain/src/index.test.ts
new file mode 100644
index 0000000..8545f7a
--- /dev/null
+++ b/packages/domain/src/index.test.ts
@@ -0,0 +1,14 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { calculateCnyAmount, currencyMinorUnits } from "./index.js";
+
+test("currency metadata uses zero minor units for JPY", () => {
+  assert.equal(currencyMinorUnits("JPY"), 0);
+  assert.equal(currencyMinorUnits("THB"), 2);
+});
+
+test("currency conversion rounds to the nearest CNY fen", () => {
+  assert.equal(calculateCnyAmount(12345, "THB", "0.201010000000"), 2481);
+  assert.equal(calculateCnyAmount(2500, "USD", "6.773000000000"), 16933);
+  assert.equal(calculateCnyAmount(1234, "JPY", "0.0473"), 5837);
+});
diff --git a/packages/domain/src/index.ts b/packages/domain/src/index.ts
index 2530b8f..b030a04 100644
--- a/packages/domain/src/index.ts
+++ b/packages/domain/src/index.ts
@@ -1,8 +1,55 @@
 export type EntryType = "expense" | "income";
 
-export type CurrencyCode = "CNY" | "USD" | "EUR" | "JPY" | "HKD";
+export const currencies = {
+  CNY: { name: "人民币", symbol: "¥", minorUnits: 2 },
+  USD: { name: "美元", symbol: "$", minorUnits: 2 },
+  EUR: { name: "欧元", symbol: "€", minorUnits: 2 },
+  JPY: { name: "日元", symbol: "¥", minorUnits: 0 },
+  THB: { name: "泰铢", symbol: "฿", minorUnits: 2 },
+  HKD: { name: "港币", symbol: "HK$", minorUnits: 2 },
+} as const;
+
+export type CurrencyCode = keyof typeof currencies;
 
 export type ExchangeRateSource = "manual" | "system";
+export type ConversionStatus = "exact" | "fallback" | "pending";
+
+export function currencyMinorUnits(currency: CurrencyCode) {
+  return currencies[currency].minorUnits;
+}
+
+export function formatCurrencyAmount(amount: number, currency: CurrencyCode, includeSymbol = true) {
+  const minorUnits = currencyMinorUnits(currency);
+  return new Intl.NumberFormat("zh-CN", {
+    style: includeSymbol ? "currency" : "decimal",
+    currency: includeSymbol ? currency : undefined,
+    currencyDisplay: "narrowSymbol",
+    minimumFractionDigits: minorUnits,
+    maximumFractionDigits: minorUnits,
+  }).format(amount / 10 ** minorUnits);
+}
+
+function decimalParts(value: string) {
+  if (!/^\d+(?:\.\d+)?$/.test(value)) throw new Error("Invalid decimal rate");
+  const [integer, fraction = ""] = value.split(".");
+  return {
+    scaled: BigInt(`${integer}${fraction}`),
+    scale: 10n ** BigInt(fraction.length),
+  };
+}
+
+export function calculateCnyAmount(amount: number, currency: CurrencyCode, cnyPerUnit: string) {
+  if (!Number.isSafeInteger(amount) || amount <= 0) throw new Error("Invalid amount");
+  const { scaled, scale } = decimalParts(cnyPerUnit);
+  const divisor = (10n ** BigInt(currencyMinorUnits(currency))) * scale;
+  const numerator = BigInt(amount) * scaled * 100n;
+  const result = (numerator + divisor / 2n) / divisor;
+  const numeric = Number(result);
+  if (!Number.isSafeInteger(numeric) || numeric <= 0 || numeric > 2_147_483_647) {
+    throw new Error("Converted amount is out of range");
+  }
+  return numeric;
+}
 
 export const ledgerThemeAccents = {
   jade: "#087f72",
@@ -29,9 +76,12 @@ export type LedgerEntry = {
   amount: number;
   currency: CurrencyCode;
   baseCurrency: CurrencyCode;
-  baseAmount: number;
-  exchangeRate: string;
+  baseAmount: number | null;
+  exchangeRate: string | null;
+  exchangeRateDate: string;
+  exchangeRateEffectiveDate: string | null;
   exchangeRateSource: ExchangeRateSource;
+  conversionStatus: ConversionStatus;
   categoryId: string;
   note: string;
   occurredAt: string;
diff --git a/services/api/src/db.ts b/services/api/src/db.ts
index 864f14b..f824479 100644
--- a/services/api/src/db.ts
+++ b/services/api/src/db.ts
@@ -103,10 +103,13 @@ CREATE TABLE IF NOT EXISTS entries (
   type varchar(8) NOT NULL CHECK (type IN ('expense', 'income')),
   amount integer NOT NULL CHECK (amount > 0),
   currency varchar(3) NOT NULL,
-  base_currency varchar(3) NOT NULL,
-  base_amount integer NOT NULL CHECK (base_amount > 0),
-  exchange_rate varchar(32) NOT NULL,
+  base_currency varchar(3) NOT NULL DEFAULT 'CNY',
+  base_amount integer CHECK (base_amount > 0),
+  exchange_rate varchar(32),
+  exchange_rate_date date,
+  exchange_rate_effective_date date,
   exchange_rate_source varchar(8) NOT NULL CHECK (exchange_rate_source IN ('manual', 'system')),
+  conversion_status varchar(8) NOT NULL DEFAULT 'pending',
   category_id varchar(100) NOT NULL,
   note varchar(500) NOT NULL DEFAULT '',
   occurred_at timestamptz NOT NULL,
@@ -122,6 +125,57 @@ CREATE TABLE IF NOT EXISTS entries (
 ALTER TABLE entries ADD COLUMN IF NOT EXISTS owner_id text REFERENCES users(id) ON DELETE CASCADE;
 UPDATE entries SET owner_id = COALESCE(created_by, updated_by) WHERE owner_id IS NULL;
 ALTER TABLE entries ALTER COLUMN owner_id SET NOT NULL;
+ALTER TABLE entries ALTER COLUMN base_amount DROP NOT NULL;
+ALTER TABLE entries ALTER COLUMN exchange_rate DROP NOT NULL;
+ALTER TABLE entries ADD COLUMN IF NOT EXISTS exchange_rate_date date;
+ALTER TABLE entries ADD COLUMN IF NOT EXISTS exchange_rate_effective_date date;
+ALTER TABLE entries ADD COLUMN IF NOT EXISTS conversion_status varchar(8) NOT NULL DEFAULT 'pending';
+UPDATE entries
+   SET base_currency = 'CNY',
+       base_amount = amount,
+       exchange_rate = '1',
+       exchange_rate_date = COALESCE(exchange_rate_date, (occurred_at AT TIME ZONE 'Asia/Shanghai')::date),
+       exchange_rate_effective_date = COALESCE(exchange_rate_effective_date, (occurred_at AT TIME ZONE 'Asia/Shanghai')::date),
+       exchange_rate_source = 'system',
+       conversion_status = 'exact'
+ WHERE currency = 'CNY';
+UPDATE entries
+   SET base_currency = 'CNY',
+       base_amount = NULL,
+       exchange_rate = NULL,
+       exchange_rate_date = COALESCE(exchange_rate_date, (occurred_at AT TIME ZONE 'Asia/Shanghai')::date),
+       exchange_rate_effective_date = NULL,
+       exchange_rate_source = 'system',
+       conversion_status = 'pending'
+ WHERE currency <> 'CNY'
+   AND exchange_rate = '1'
+   AND exchange_rate_source = 'manual';
+UPDATE entries
+   SET base_currency = 'CNY',
+       exchange_rate_effective_date = COALESCE(
+         exchange_rate_effective_date,
+         exchange_rate_date,
+         (occurred_at AT TIME ZONE 'Asia/Shanghai')::date
+       ),
+       conversion_status = 'fallback'
+ WHERE currency <> 'CNY'
+   AND base_amount IS NOT NULL
+   AND exchange_rate IS NOT NULL
+   AND conversion_status = 'pending';
+UPDATE entries
+   SET exchange_rate_date = (occurred_at AT TIME ZONE 'Asia/Shanghai')::date
+ WHERE exchange_rate_date IS NULL;
+ALTER TABLE entries ALTER COLUMN exchange_rate_date SET NOT NULL;
+ALTER TABLE entries DROP CONSTRAINT IF EXISTS entries_conversion_status_check;
+ALTER TABLE entries ADD CONSTRAINT entries_conversion_status_check
+  CHECK (conversion_status IN ('exact', 'fallback', 'pending'));
+ALTER TABLE entries DROP CONSTRAINT IF EXISTS entries_conversion_values_check;
+ALTER TABLE entries ADD CONSTRAINT entries_conversion_values_check
+  CHECK (
+    (conversion_status = 'pending' AND base_amount IS NULL AND exchange_rate IS NULL)
+    OR
+    (conversion_status IN ('exact', 'fallback') AND base_amount > 0 AND exchange_rate IS NOT NULL)
+  );
 
 CREATE TABLE IF NOT EXISTS entry_ledgers (
   entry_id text NOT NULL REFERENCES entries(id) ON DELETE CASCADE,
@@ -160,6 +214,36 @@ CREATE TABLE IF NOT EXISTS entry_sync_operations (
   user_id text NOT NULL REFERENCES users(id) ON DELETE CASCADE,
   processed_at timestamptz NOT NULL DEFAULT now()
 );
+
+CREATE TABLE IF NOT EXISTS exchange_rates (
+  currency varchar(3) NOT NULL,
+  rate_date date NOT NULL,
+  cny_per_unit numeric(24, 12) NOT NULL CHECK (cny_per_unit > 0),
+  provider varchar(64) NOT NULL,
+  provider_rate_date date NOT NULL,
+  fetched_at timestamptz NOT NULL,
+  created_at timestamptz NOT NULL DEFAULT now(),
+  updated_at timestamptz NOT NULL DEFAULT now(),
+  PRIMARY KEY (currency, rate_date)
+);
+
+CREATE INDEX IF NOT EXISTS exchange_rates_currency_date
+  ON exchange_rates (currency, rate_date DESC);
+
+CREATE TABLE IF NOT EXISTS entry_conversion_jobs (
+  entry_id text PRIMARY KEY REFERENCES entries(id) ON DELETE CASCADE,
+  target_version integer NOT NULL,
+  attempts integer NOT NULL DEFAULT 0,
+  available_at timestamptz NOT NULL DEFAULT now(),
+  locked_at timestamptz,
+  lock_token text,
+  last_error text,
+  created_at timestamptz NOT NULL DEFAULT now(),
+  updated_at timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS entry_conversion_jobs_available
+  ON entry_conversion_jobs (available_at, created_at);
 `;
 
 export async function initializeDatabase() {
@@ -191,6 +275,12 @@ export async function initializeDatabase() {
          SET unlinked_at = NULL, updated_at = now()
        WHERE entry_ledgers.unlinked_at IS NOT NULL`,
     );
+    await client.query(
+      `INSERT INTO entry_conversion_jobs (entry_id, target_version)
+       SELECT id, version FROM entries
+        WHERE conversion_status IN ('pending', 'fallback') AND deleted_at IS NULL
+       ON CONFLICT (entry_id) DO NOTHING`,
+    );
     await client.query("COMMIT");
   } catch (error) {
     await client.query("ROLLBACK");
diff --git a/services/api/src/exchange-rates.ts b/services/api/src/exchange-rates.ts
new file mode 100644
index 0000000..3401814
--- /dev/null
+++ b/services/api/src/exchange-rates.ts
@@ -0,0 +1,360 @@
+import { randomUUID } from "node:crypto";
+import { calculateCnyAmount, currencies, type CurrencyCode, type ConversionStatus } from "@cents/domain";
+import type { PoolClient } from "pg";
+import { pool } from "./db.js";
+
+const PROVIDER = "ECB";
+const API_BASE_URL = process.env.EXCHANGE_RATE_API_URL ?? "https://api.frankfurter.dev";
+const APP_TIME_ZONE = process.env.APP_TIME_ZONE ?? "Asia/Shanghai";
+const CACHE_LIMIT = 2_000;
+const CURRENT_RATE_TTL_MS = 15 * 60_000;
+const FALLBACK_TTL_MS = 5 * 60_000;
+const PENDING_TTL_MS = 30_000;
+const WORKER_INTERVAL_MS = 1_000;
+
+export type ResolvedRate = {
+  currency: CurrencyCode;
+  requestedDate: string;
+  effectiveDate: string | null;
+  cnyPerUnit: string | null;
+  status: ConversionStatus;
+};
+
+type CachedRate = ResolvedRate & { expiresAt: number };
+type StoredRate = {
+  currency: CurrencyCode;
+  requestedDate: string;
+  effectiveDate: string;
+  cnyPerUnit: string;
+};
+
+const rateCache = new Map<string, CachedRate>();
+const inFlight = new Map<string, Promise<ResolvedRate>>();
+let workerTimer: NodeJS.Timeout | null = null;
+let workerRunning = false;
+
+function cacheKey(currency: CurrencyCode, requestedDate: string) {
+  return `${PROVIDER}:${currency}:${requestedDate}`;
+}
+
+function isToday(date: string) {
+  const parts = new Intl.DateTimeFormat("en-CA", {
+    timeZone: APP_TIME_ZONE,
+    year: "numeric",
+    month: "2-digit",
+    day: "2-digit",
+  }).formatToParts(new Date());
+  const value = Object.fromEntries(parts.map((part) => [part.type, part.value]));
+  return date === `${value.year}-${value.month}-${value.day}`;
+}
+
+function cacheResult(result: ResolvedRate) {
+  const ttl = result.status === "pending"
+    ? PENDING_TTL_MS
+    : result.status === "fallback"
+      ? FALLBACK_TTL_MS
+      : isToday(result.requestedDate) ? CURRENT_RATE_TTL_MS : Number.POSITIVE_INFINITY;
+  const key = cacheKey(result.currency, result.requestedDate);
+  rateCache.delete(key);
+  rateCache.set(key, { ...result, expiresAt: Date.now() + ttl });
+  while (rateCache.size > CACHE_LIMIT) {
+    const oldestKey = rateCache.keys().next().value as string | undefined;
+    if (!oldestKey) break;
+    rateCache.delete(oldestKey);
+  }
+}
+
+function readCache(currency: CurrencyCode, requestedDate: string) {
+  const key = cacheKey(currency, requestedDate);
+  const cached = rateCache.get(key);
+  if (!cached) return null;
+  if (cached.expiresAt <= Date.now()) {
+    rateCache.delete(key);
+    return null;
+  }
+  rateCache.delete(key);
+  rateCache.set(key, cached);
+  return cached;
+}
+
+async function databaseRates(currency: CurrencyCode, requestedDate: string) {
+  const result = await pool.query<{
+    currency: CurrencyCode;
+    requestedDate: string;
+    effectiveDate: string;
+    cnyPerUnit: string;
+    exact: boolean;
+  }>(
+    `SELECT currency, rate_date::text AS "requestedDate",
+            provider_rate_date::text AS "effectiveDate",
+            cny_per_unit::text AS "cnyPerUnit",
+            rate_date = $2::date AS exact
+       FROM exchange_rates
+      WHERE currency = $1
+      ORDER BY
+        (rate_date = $2::date) DESC,
+        (rate_date <= $2::date) DESC,
+        CASE WHEN rate_date <= $2::date THEN $2::date - rate_date ELSE rate_date - $2::date END
+      LIMIT 1`,
+    [currency, requestedDate],
+  );
+  const row = result.rows[0];
+  if (!row) return null;
+  return {
+    currency: row.currency,
+    requestedDate: toDateString(row.requestedDate),
+    effectiveDate: toDateString(row.effectiveDate),
+    cnyPerUnit: row.cnyPerUnit,
+    exact: row.exact,
+  };
+}
+
+async function fetchProviderRate(currency: CurrencyCode, requestedDate: string): Promise<StoredRate> {
+  const url = new URL(`/v2/rate/${currency}/CNY`, API_BASE_URL);
+  url.searchParams.set("date", requestedDate);
+  url.searchParams.set("providers", PROVIDER);
+  const response = await fetch(url, { signal: AbortSignal.timeout(4_000) });
+  if (!response.ok) throw new Error(`Frankfurter returned HTTP ${response.status}`);
+  const value = await response.json() as Partial<{ date: string; base: string; quote: string; rate: number }>;
+  if (
+    value.base !== currency
+    || value.quote !== "CNY"
+    || typeof value.date !== "string"
+    || !/^\d{4}-\d{2}-\d{2}$/.test(value.date)
+    || typeof value.rate !== "number"
+    || !Number.isFinite(value.rate)
+    || value.rate <= 0
+  ) {
+    throw new Error("Frankfurter returned an invalid rate");
+  }
+  return {
+    currency,
+    requestedDate,
+    effectiveDate: value.date,
+    cnyPerUnit: String(value.rate),
+  };
+}
+
+async function persistRate(rate: StoredRate) {
+  await pool.query(
+    `INSERT INTO exchange_rates (
+       currency, rate_date, cny_per_unit, provider, provider_rate_date, fetched_at
+     ) VALUES ($1, $2, $3, $4, $5, now())
+     ON CONFLICT (currency, rate_date) DO UPDATE SET
+       cny_per_unit = EXCLUDED.cny_per_unit,
+       provider = EXCLUDED.provider,
+       provider_rate_date = EXCLUDED.provider_rate_date,
+       fetched_at = EXCLUDED.fetched_at,
+       updated_at = now()`,
+    [rate.currency, rate.requestedDate, rate.cnyPerUnit, PROVIDER, rate.effectiveDate],
+  );
+}
+
+async function resolveUncached(currency: CurrencyCode, requestedDate: string): Promise<ResolvedRate> {
+  const stored = await databaseRates(currency, requestedDate);
+  if (stored?.exact) {
+    return {
+      currency,
+      requestedDate,
+      effectiveDate: stored.effectiveDate,
+      cnyPerUnit: stored.cnyPerUnit,
+      status: "exact",
+    };
+  }
+  try {
+    const providerRate = await fetchProviderRate(currency, requestedDate);
+    await persistRate(providerRate);
+    return {
+      currency,
+      requestedDate,
+      effectiveDate: providerRate.effectiveDate,
+      cnyPerUnit: providerRate.cnyPerUnit,
+      status: "exact",
+    };
+  } catch (error) {
+    if (stored) {
+      return {
+        currency,
+        requestedDate,
+        effectiveDate: stored.effectiveDate,
+        cnyPerUnit: stored.cnyPerUnit,
+        status: "fallback",
+      };
+    }
+    console.error("Failed to resolve exchange rate", { currency, requestedDate, error });
+    return { currency, requestedDate, effectiveDate: null, cnyPerUnit: null, status: "pending" };
+  }
+}
+
+export async function resolveExchangeRate(currency: CurrencyCode, requestedDate: string): Promise<ResolvedRate> {
+  if (currency === "CNY") {
+    return { currency, requestedDate, effectiveDate: requestedDate, cnyPerUnit: "1", status: "exact" };
+  }
+  const cached = readCache(currency, requestedDate);
+  if (cached) return cached;
+  const key = cacheKey(currency, requestedDate);
+  const active = inFlight.get(key);
+  if (active) return active;
+  const request = resolveUncached(currency, requestedDate).then((result) => {
+    cacheResult(result);
+    return result;
+  }).finally(() => inFlight.delete(key));
+  inFlight.set(key, request);
+  return request;
+}
+
+export async function enqueueConversion(client: PoolClient, entryId: string, targetVersion: number) {
+  await client.query(
+    `INSERT INTO entry_conversion_jobs (entry_id, target_version)
+     VALUES ($1, $2)
+     ON CONFLICT (entry_id) DO UPDATE SET
+       target_version = EXCLUDED.target_version,
+       attempts = 0,
+       available_at = now(),
+       locked_at = NULL,
+       lock_token = NULL,
+       last_error = NULL,
+       updated_at = now()`,
+    [entryId, targetVersion],
+  );
+}
+
+async function claimJob() {
+  const lockToken = randomUUID();
+  const result = await pool.query<{ entryId: string; targetVersion: number; attempts: number }>(
+    `UPDATE entry_conversion_jobs
+        SET locked_at = now(), lock_token = $1, updated_at = now()
+      WHERE entry_id = (
+        SELECT entry_id FROM entry_conversion_jobs
+         WHERE available_at <= now()
+           AND (locked_at IS NULL OR locked_at < now() - interval '2 minutes')
+         ORDER BY available_at, created_at
+         FOR UPDATE SKIP LOCKED
+         LIMIT 1
+      )
+      RETURNING entry_id AS "entryId", target_version AS "targetVersion", attempts`,
+    [lockToken],
+  );
+  return result.rows[0] ? { ...result.rows[0], lockToken } : null;
+}
+
+async function completeJob(job: Awaited<ReturnType<typeof claimJob>>) {
+  if (!job) return;
+  const entryResult = await pool.query<{
+    id: string;
+    amount: number;
+    currency: CurrencyCode;
+    exchangeRateDate: string;
+    version: number;
+    deletedAt: Date | null;
+  }>(
+    `SELECT id, amount, currency, exchange_rate_date::text AS "exchangeRateDate",
+            version, deleted_at AS "deletedAt"
+       FROM entries WHERE id = $1`,
+    [job.entryId],
+  );
+  const entry = entryResult.rows[0];
+  if (!entry || entry.deletedAt) {
+    await pool.query("DELETE FROM entry_conversion_jobs WHERE entry_id = $1 AND lock_token = $2", [job.entryId, job.lockToken]);
+    return;
+  }
+  if (entry.version !== job.targetVersion) {
+    await pool.query(
+      `UPDATE entry_conversion_jobs SET target_version = $1, attempts = 0,
+              available_at = now(), locked_at = NULL, lock_token = NULL, updated_at = now()
+        WHERE entry_id = $2 AND lock_token = $3`,
+      [entry.version, entry.id, job.lockToken],
+    );
+    return;
+  }
+
+  const requestedDate = toDateString(entry.exchangeRateDate);
+  try {
+    const rate = await resolveExchangeRate(entry.currency, requestedDate);
+    if (!rate.cnyPerUnit || !rate.effectiveDate || rate.status === "pending") {
+      throw new Error("No exchange rate is available");
+    }
+    const baseAmount = calculateCnyAmount(entry.amount, entry.currency, rate.cnyPerUnit);
+    const client = await pool.connect();
+    try {
+      await client.query("BEGIN");
+      const updated = await client.query(
+        `UPDATE entries SET
+           base_currency = 'CNY',
+           base_amount = $1,
+           exchange_rate = $2,
+           exchange_rate_effective_date = $3,
+           exchange_rate_source = 'system',
+           conversion_status = $4,
+           server_updated_at = now()
+         WHERE id = $5 AND version = $6`,
+        [baseAmount, rate.cnyPerUnit, rate.effectiveDate, rate.status, entry.id, entry.version],
+      );
+      if (!updated.rowCount) {
+        await client.query(
+          `UPDATE entry_conversion_jobs SET locked_at = NULL, lock_token = NULL,
+                  available_at = now(), updated_at = now()
+            WHERE entry_id = $1 AND lock_token = $2`,
+          [entry.id, job.lockToken],
+        );
+      } else if (rate.status === "exact") {
+        await client.query(
+          "DELETE FROM entry_conversion_jobs WHERE entry_id = $1 AND lock_token = $2",
+          [entry.id, job.lockToken],
+        );
+      } else {
+        await client.query(
+          `UPDATE entry_conversion_jobs SET attempts = attempts + 1,
+                  available_at = now() + interval '1 hour',
+                  locked_at = NULL, lock_token = NULL, last_error = NULL, updated_at = now()
+            WHERE entry_id = $1 AND lock_token = $2`,
+          [entry.id, job.lockToken],
+        );
+      }
+      await client.query("COMMIT");
+    } catch (error) {
+      await client.query("ROLLBACK");
+      throw error;
+    } finally {
+      client.release();
+    }
+  } catch (error) {
+    const delayMinutes = Math.min(60, 2 ** Math.min(job.attempts, 5));
+    await pool.query(
+      `UPDATE entry_conversion_jobs SET attempts = attempts + 1,
+              available_at = now() + ($1 * interval '1 minute'),
+              locked_at = NULL, lock_token = NULL, last_error = $2, updated_at = now()
+        WHERE entry_id = $3 AND lock_token = $4`,
+      [delayMinutes, error instanceof Error ? error.message.slice(0, 500) : "Unknown conversion error", entry.id, job.lockToken],
+    );
+  }
+}
+
+async function runWorker() {
+  if (workerRunning) return;
+  workerRunning = true;
+  try {
+    for (let count = 0; count < 10; count += 1) {
+      const job = await claimJob();
+      if (!job) break;
+      await completeJob(job);
+    }
+  } finally {
+    workerRunning = false;
+  }
+}
+
+export function startExchangeRateWorker() {
+  if (workerTimer) return;
+  void runWorker();
+  workerTimer = setInterval(() => void runWorker(), WORKER_INTERVAL_MS);
+  workerTimer.unref();
+}
+
+function toDateString(value: string) {
+  return value.slice(0, 10);
+}
+
+export function isCurrencyCode(value: unknown): value is CurrencyCode {
+  return typeof value === "string" && Object.hasOwn(currencies, value);
+}
diff --git a/services/api/src/server.ts b/services/api/src/server.ts
index 9ca6e40..75dcb24 100644
--- a/services/api/src/server.ts
+++ b/services/api/src/server.ts
@@ -1,10 +1,22 @@
 import cookie from "@fastify/cookie";
 import helmet from "@fastify/helmet";
 import rateLimit from "@fastify/rate-limit";
-import { ledgerThemeAccents, type LedgerEntry, type LedgerThemeId, type SyncOperation } from "@cents/domain";
+import {
+  ledgerThemeAccents,
+  type CurrencyCode,
+  type LedgerEntry,
+  type LedgerThemeId,
+  type SyncOperation,
+} from "@cents/domain";
 import Fastify, { type FastifyReply, type FastifyRequest } from "fastify";
 import { createUserWithPersonalLedger, PERSONAL_LEDGER_NAME } from "./accounts.js";
 import { initializeDatabase, pool } from "./db.js";
+import {
+  enqueueConversion,
+  isCurrencyCode,
+  resolveExchangeRate,
+  startExchangeRateWorker,
+} from "./exchange-rates.js";
 import {
   clearSessionCookie,
   createId,
@@ -28,6 +40,7 @@ await server.register(cookie);
 await server.register(helmet, { contentSecurityPolicy: false });
 await server.register(rateLimit, { max: 120, timeWindow: "1 minute" });
 await initializeDatabase();
+startExchangeRateWorker();
 
 server.addHook("onRequest", async (request, reply) => {
   if (!["POST", "PATCH", "PUT", "DELETE"].includes(request.method)) return;
@@ -48,6 +61,7 @@ server.addHook("onSend", async (request, reply, payload) => {
     request.url.startsWith("/api/auth/")
     || request.url.startsWith("/api/invitations/")
     || request.url.startsWith("/api/ledger-invitations/")
+    || request.url.startsWith("/api/exchange-rates/")
     || request.url.startsWith("/api/sync/")
     || request.url === "/api/me"
   ) {
@@ -115,8 +129,6 @@ function invitationStatus(invitation: { expiresAt: Date | string; acceptedAt: Da
   return "valid";
 }
 
-const currencies = new Set(["CNY", "USD", "EUR", "JPY", "HKD"]);
-
 function validLedgerTheme(value: unknown): value is LedgerThemeId {
   return typeof value === "string" && Object.hasOwn(ledgerThemeAccents, value);
 }
@@ -131,6 +143,11 @@ function validDate(value: unknown) {
   return typeof value === "string" && !Number.isNaN(Date.parse(value));
 }
 
+function validDateOnly(value: unknown) {
+  return typeof value === "string" && /^\d{4}-\d{2}-\d{2}$/.test(value)
+    && !Number.isNaN(Date.parse(`${value}T00:00:00Z`));
+}
+
 function validLedgerIds(value: unknown): value is string[] {
   return Array.isArray(value) && value.length > 0 && value.length <= 20
     && value.every((ledgerId) => typeof ledgerId === "string" && ledgerId.length > 0 && ledgerId.length <= 100)
@@ -145,11 +162,19 @@ function validEntry(value: unknown): value is LedgerEntry {
     && validLedgerIds(entry.ledgerIds)
     && (entry.type === "expense" || entry.type === "income")
     && Number.isSafeInteger(entry.amount) && entry.amount! > 0 && entry.amount! <= 2_147_483_647
-    && typeof entry.currency === "string" && currencies.has(entry.currency)
-    && typeof entry.baseCurrency === "string" && currencies.has(entry.baseCurrency)
-    && Number.isSafeInteger(entry.baseAmount) && entry.baseAmount! > 0 && entry.baseAmount! <= 2_147_483_647
-    && typeof entry.exchangeRate === "string" && entry.exchangeRate.length > 0 && entry.exchangeRate.length <= 32
+    && isCurrencyCode(entry.currency)
+    && entry.baseCurrency === "CNY"
+    && (entry.baseAmount === null
+      || (Number.isSafeInteger(entry.baseAmount) && entry.baseAmount! > 0 && entry.baseAmount! <= 2_147_483_647))
+    && (entry.exchangeRate === null
+      || (typeof entry.exchangeRate === "string" && /^\d+(?:\.\d+)?$/.test(entry.exchangeRate) && entry.exchangeRate.length <= 32))
+    && validDateOnly(entry.exchangeRateDate)
+    && (entry.exchangeRateEffectiveDate === null || validDateOnly(entry.exchangeRateEffectiveDate))
     && (entry.exchangeRateSource === "manual" || entry.exchangeRateSource === "system")
+    && (entry.conversionStatus === "exact" || entry.conversionStatus === "fallback" || entry.conversionStatus === "pending")
+    && (entry.conversionStatus === "pending"
+      ? entry.baseAmount === null && entry.exchangeRate === null
+      : entry.baseAmount !== null && entry.exchangeRate !== null && entry.exchangeRateEffectiveDate !== null)
     && typeof entry.categoryId === "string" && entry.categoryId.length > 0 && entry.categoryId.length <= 100
     && typeof entry.note === "string" && entry.note.length <= 500
     && validDate(entry.occurredAt) && validDate(entry.createdAt) && validDate(entry.updatedAt)
@@ -267,7 +292,7 @@ server.post<{ Body: { name?: string; color?: string; theme?: string; defaultCurr
     const defaultCurrency = request.body.defaultCurrency ?? "CNY";
     if (!name || name.length > 40) return reply.code(400).send({ error: "账本名称应为 1 至 40 个字符" });
     if (!/^#[0-9a-f]{6}$/i.test(color)) return reply.code(400).send({ error: "账本颜色无效" });
-    if (!["CNY", "USD", "EUR", "JPY", "HKD"].includes(defaultCurrency)) {
+    if (!isCurrencyCode(defaultCurrency)) {
       return reply.code(400).send({ error: "默认币种无效" });
     }
 
@@ -331,16 +356,31 @@ server.patch<{
   }
   const theme = request.body.theme ?? ledgerThemeFromColor(request.body.color);
   const color = ledgerThemeAccents[theme];
+  const defaultCurrency = request.body.defaultCurrency ?? "CNY";
+  if (!isCurrencyCode(defaultCurrency)) return reply.code(400).send({ error: "默认币种无效" });
   const result = await pool.query(
     `UPDATE ledgers SET name = $1, color = $2, theme = $3, default_currency = $4, updated_at = now()
       WHERE id = $5
       RETURNING id, name, color, theme, default_currency AS "defaultCurrency",
                 created_at AS "createdAt", updated_at AS "updatedAt", archived_at AS "archivedAt"`,
-    [personalLedger.rows[0]?.isPersonal ? PERSONAL_LEDGER_NAME : name, color, theme, request.body.defaultCurrency ?? "CNY", request.params.ledgerId],
+    [personalLedger.rows[0]?.isPersonal ? PERSONAL_LEDGER_NAME : name, color, theme, defaultCurrency, request.params.ledgerId],
   );
   return { ledger: result.rows[0] };
 });
 
+server.get<{
+  Params: { currency: string; date: string };
+}>("/api/exchange-rates/:currency/:date", async (request, reply) => {
+  const user = await requireUser(request, reply);
+  if (!user) return;
+  if (!isCurrencyCode(request.params.currency) || !validDateOnly(request.params.date)) {
+    return reply.code(400).send({ error: "币种或汇率日期无效" });
+  }
+  return {
+    rate: await resolveExchangeRate(request.params.currency, request.params.date),
+  };
+});
+
 // Application invitations create accounts but never grant access to an existing ledger.
 server.get<{ Params: { key: string } }>("/api/invitations/:key", async (request, reply) => {
   const user = await currentUser(request, reply);
@@ -515,14 +555,30 @@ server.post<{ Body: { operations?: unknown[] } }>("/api/sync/push", async (reque
         continue;
       }
 
-      const existing = await client.query<{ ownerId: string; canAccess: boolean }>(
+      const existing = await client.query<{
+        ownerId: string;
+        canAccess: boolean;
+        amount: number;
+        currency: CurrencyCode;
+        exchangeRateDate: string;
+        baseAmount: number | null;
+        exchangeRate: string | null;
+        exchangeRateEffectiveDate: string | null;
+        exchangeRateSource: "manual" | "system";
+        conversionStatus: "exact" | "fallback" | "pending";
+      }>(
         `SELECT e.owner_id AS "ownerId",
                 (e.owner_id = $2 OR EXISTS (
                   SELECT 1 FROM entry_ledgers el
                   JOIN ledger_members m ON m.ledger_id = el.ledger_id
                   WHERE el.entry_id = e.id AND el.unlinked_at IS NULL
                     AND m.user_id = $2 AND m.removed_at IS NULL
-                )) AS "canAccess"
+                )) AS "canAccess",
+                e.amount, e.currency, e.exchange_rate_date::text AS "exchangeRateDate",
+                e.base_amount AS "baseAmount", e.exchange_rate AS "exchangeRate",
+                e.exchange_rate_effective_date::text AS "exchangeRateEffectiveDate",
+                e.exchange_rate_source AS "exchangeRateSource",
+                e.conversion_status AS "conversionStatus"
            FROM entries e WHERE e.id = $1`,
         [operation.entityId, user.id],
       );
@@ -557,14 +613,44 @@ server.post<{ Body: { operations?: unknown[] } }>("/api/sync/push", async (reque
       const targetLedgerIds = [...new Set([...operation.ledgerIds, personalLedger.rows[0].id])];
 
       const entry = operation.payload;
+      const existingEntry = existing.rows[0];
+      const existingRateDate = existingEntry?.exchangeRateDate?.slice(0, 10);
+      const conversionChanged = !existingEntry
+        || existingEntry.amount !== entry.amount
+        || existingEntry.currency !== entry.currency
+        || existingRateDate !== entry.exchangeRateDate;
+      const conversion = entry.currency === "CNY"
+        ? {
+            baseAmount: entry.amount,
+            exchangeRate: "1",
+            effectiveDate: entry.exchangeRateDate,
+            source: "system" as const,
+            status: "exact" as const,
+          }
+        : !conversionChanged && existingEntry
+          ? {
+              baseAmount: existingEntry.baseAmount,
+              exchangeRate: existingEntry.exchangeRate,
+              effectiveDate: existingEntry.exchangeRateEffectiveDate,
+              source: existingEntry.exchangeRateSource,
+              status: existingEntry.conversionStatus,
+            }
+          : {
+              baseAmount: null,
+              exchangeRate: null,
+              effectiveDate: null,
+              source: "system" as const,
+              status: "pending" as const,
+            };
       const writeResult = await client.query(
         `INSERT INTO entries (
            id, owner_id, type, amount, currency, base_currency, base_amount,
-           exchange_rate, exchange_rate_source, category_id, note, occurred_at,
+           exchange_rate, exchange_rate_date, exchange_rate_effective_date,
+           exchange_rate_source, conversion_status, category_id, note, occurred_at,
            created_by, updated_by, created_at, updated_at, deleted_at, version
          ) VALUES (
-           $1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12,
-           $13, $14, $15, $16, $17, $18
+           $1, $2, $3, $4, $5, 'CNY', $6, $7, $8, $9, $10, $11, $12, $13,
+           $14, $15, $16, $17, $18, $19, $20
          )
          ON CONFLICT (id) DO UPDATE SET
            type = EXCLUDED.type,
@@ -573,7 +659,10 @@ server.post<{ Body: { operations?: unknown[] } }>("/api/sync/push", async (reque
            base_currency = EXCLUDED.base_currency,
            base_amount = EXCLUDED.base_amount,
            exchange_rate = EXCLUDED.exchange_rate,
+           exchange_rate_date = EXCLUDED.exchange_rate_date,
+           exchange_rate_effective_date = EXCLUDED.exchange_rate_effective_date,
            exchange_rate_source = EXCLUDED.exchange_rate_source,
+           conversion_status = EXCLUDED.conversion_status,
            category_id = EXCLUDED.category_id,
            note = EXCLUDED.note,
            occurred_at = EXCLUDED.occurred_at,
@@ -585,8 +674,9 @@ server.post<{ Body: { operations?: unknown[] } }>("/api/sync/push", async (reque
         WHERE entries.version < EXCLUDED.version
             OR (entries.version = EXCLUDED.version AND entries.updated_at <= EXCLUDED.updated_at)`,
         [
-          entry.id, user.id, entry.type, entry.amount, entry.currency, entry.baseCurrency,
-          entry.baseAmount, entry.exchangeRate, entry.exchangeRateSource, entry.categoryId,
+          entry.id, user.id, entry.type, entry.amount, entry.currency,
+          conversion.baseAmount, conversion.exchangeRate, entry.exchangeRateDate,
+          conversion.effectiveDate, conversion.source, conversion.status, entry.categoryId,
           entry.note, entry.occurredAt, user.id, user.id, entry.createdAt, entry.updatedAt,
           entry.deletedAt, entry.version,
         ],
@@ -617,6 +707,14 @@ server.post<{ Body: { operations?: unknown[] } }>("/api/sync/push", async (reque
           [entry.id, targetLedgerIds],
         );
       }
+      if (
+        writeResult.rowCount
+        && operation.action !== "delete"
+        && entry.currency !== "CNY"
+        && (conversionChanged || conversion.status !== "exact")
+      ) {
+        await enqueueConversion(client, entry.id, entry.version);
+      }
       await client.query("UPDATE entries SET server_updated_at = now() WHERE id = $1", [entry.id]);
       await client.query(
         "INSERT INTO entry_sync_operations (id, user_id) VALUES ($1, $2)",
@@ -655,7 +753,11 @@ server.get<{ Querystring: { cursor?: string } }>("/api/sync/pull", async (reques
             ) AS "ledgerIds",
             e.type, e.amount,
             e.currency, e.base_currency AS "baseCurrency", e.base_amount AS "baseAmount",
-            e.exchange_rate AS "exchangeRate", e.exchange_rate_source AS "exchangeRateSource",
+            e.exchange_rate AS "exchangeRate",
+            e.exchange_rate_date::text AS "exchangeRateDate",
+            e.exchange_rate_effective_date::text AS "exchangeRateEffectiveDate",
+            e.exchange_rate_source AS "exchangeRateSource",
+            e.conversion_status AS "conversionStatus",
             e.category_id AS "categoryId", e.note, e.occurred_at AS "occurredAt",
             e.created_by AS "createdBy", e.updated_by AS "updatedBy",
             e.created_at AS "createdAt", e.updated_at AS "updatedAt",