@@ -4,6 +4,7 @@ import { join } from "node:path";
 import { fileURLToPath } from "node:url";
 
 import {
+  assetHistoryCoverage,
   buildAssetChartGeometry,
   buildBinanceWalletHistoryChartGeometry,
   chartRangeEmptyNote,
@@ -59,6 +60,18 @@ const points = [
 const now = Date.parse("2026-09-04T12:00:00Z");
 assert.equal(filterAssetHistoryByRange(points, "all", now).length, 3);
 assert.deepEqual(filterAssetHistoryByRange(points, "3m", now).map((row) => row.observation_date), ["2026-09-01", "2026-09-02", "2026-09-04"]);
+// Coverage is measured from the first to the last real sample; a 3y/5y/10y/all
+// selection over 4 days of history must say so instead of implying more.
+assert.equal(assetHistoryCoverage([], "1y"), null);
+assert.equal(assetHistoryCoverage([{ observation_date: "bad" }], "1y"), null);
+assert.deepEqual(assetHistoryCoverage([...points].reverse(), "3y"), { firstDate: "2026-09-01", lastDate: "2026-09-04", days: 4, shorterThanRange: true });
+assert.equal(assetHistoryCoverage(points, "10y").shorterThanRange, true);
+assert.equal(assetHistoryCoverage(points, "all").shorterThanRange, true);
+assert.equal(assetHistoryCoverage([{ observation_date: "2026-09-04" }], "3m").days, 1);
+const longPoints = Array.from({ length: 120 }, (_, index) => ({ observation_date: new Date(Date.parse("2026-05-01T00:00:00Z") + index * 86400000).toISOString().slice(0, 10) }));
+assert.equal(assetHistoryCoverage(longPoints, "3m").shorterThanRange, false);
+assert.equal(assetHistoryCoverage(longPoints, "6m").shorterThanRange, true);
+
 
 const geometry = buildAssetChartGeometry(points);
 assert.equal(geometry.dots.length, 3);
 
@@ -13,6 +13,7 @@ import {
   chartRangeEmptyNote,
   chartUnavailable,
   filterAssetHistoryByRange,
+  assetHistoryCoverage,
   formatOverviewInstant,
   formatOverviewShortInstant,
   accountNativeReadout,
@@ -511,11 +512,11 @@ export function OverviewPage({ accounts, accountFacts, accountOptionsRevision, o
   const selectedUpdatedAt = accountId === "all" ? null : accountFactsUpdatedAt(selectedFacts);
   const assetsMetricLabel = accountId === "all" ? "账户最新估值（按币种）" : selectedWalletValuation ? "钱包总资产" : "总资产";
   const selectedCashLabel = accountId === "all" ? "账户现金（按来源语义和币种）" : selectedAccount ? cashLabelForPlatform(selectedAccount.platformKey) : "可用现金";
-  const filteredWalletPoints = walletChartSelected
-    ? filterAssetHistoryByRange(historyKey === requestedHistoryKey ? walletHistory?.points || [] : [], range) : [];
-  const filteredAccountPoints = walletChartSelected
-    ? [] : filterAssetHistoryByRange(historyKey === requestedHistoryKey && accountHistory?.identity_mismatch !== true && accountHistory?.series.currency === currency
-      ? (accountHistory?.series.points || []).filter(point => point.currency === currency) : [], range);
+  const storedWalletPoints = walletChartSelected && historyKey === requestedHistoryKey ? walletHistory?.points || [] : [];
+  const storedAccountPoints = !walletChartSelected && historyKey === requestedHistoryKey && accountHistory?.identity_mismatch !== true && accountHistory?.series.currency === currency
+    ? (accountHistory?.series.points || []).filter(point => point.currency === currency) : [];
+  const filteredWalletPoints = walletChartSelected ? filterAssetHistoryByRange(storedWalletPoints, range) : [];
+  const filteredAccountPoints = walletChartSelected ? [] : filterAssetHistoryByRange(storedAccountPoints, range);
   const geometry = walletChartSelected
     ? buildBinanceWalletHistoryChartGeometry(filteredWalletPoints)
     : buildAssetChartGeometry(filteredAccountPoints);
@@ -546,6 +547,9 @@ export function OverviewPage({ accounts, accountFacts, accountOptionsRevision, o
     break_before: point.break_before,
   })), range));
   const shownGeometry = accountId === "all" ? aggregateGeometry : geometry;
+  const historyCoverage = assetHistoryCoverage(accountId === "all"
+    ? aggregateCurrencySeries
+    : walletChartSelected ? storedWalletPoints : storedAccountPoints, range);
   const benchmarkSeries = RETURN_INDEX_LEGEND.map(name => presentMarketBenchmarkSeries(storedBenchmarkPoints, name));
   const primaryBenchmark = benchmarkSeries[0];
   const benchmarkGeometry = buildBenchmarkChartGeometry(primaryBenchmark.points);
@@ -809,6 +813,7 @@ export function OverviewPage({ accounts, accountFacts, accountOptionsRevision, o
         <div className="asset-chart-meta">
           <span>{shownGeometry.dots[0]?.date} → {shownGeometry.dots[shownGeometry.dots.length - 1]?.date}</span>
           <span>{currency} {shownGeometry.minLabel} – {shownGeometry.maxLabel}</span>
+          {historyCoverage?.shorterThanRange ? <span className="asset-chart-coverage">{t("历史仅 {days} 天（自 {date} 起），不代表更长期表现。", { days: historyCoverage.days, date: historyCoverage.firstDate })}</span> : null}
           {accountId === "all" && aggregateSeries.omittedPartialDateCount > 0 ? <span>{t("有 {count} 个日期省略了缺观察的账户，线段在缺口处断开。", { count: aggregateSeries.omittedPartialDateCount })}</span> : null}
         </div>
       </div> : <div className="chart-empty">
 
@@ -992,6 +992,7 @@ export const EN_COPY = {
   "请选择账户": "Select an account",
   "加载中…": "Loading…",
   "{range}内暂无资产记录": "No asset history in {range}",
+  "历史仅 {days} 天（自 {date} 起），不代表更长期表现。": "Only {days} days of history (since {date}); this does not represent longer-term performance.",
   "只读演练": "Read-only rehearsal",
   "模拟观察": "Shadow observation",
   "验证": "Validation",
 
@@ -363,6 +363,30 @@ export function filterAssetHistoryByRange<T extends { observation_date: string }
   return sorted.filter((item) => item.observation_date >= start && item.observation_date <= end);
 }
 
+export type AssetHistoryCoverage = {
+  firstDate: string;
+  lastDate: string;
+  days: number;
+  shorterThanRange: boolean;
+};
+
+/**
+ * Real coverage of stored history, measured from the first to the last stored
+ * sample (inclusive calendar days). `shorterThanRange` is true when the
+ * selected range (or "all") is longer than what was actually stored, so the
+ * chart must say how short the history is instead of implying multi-year data.
+ */
+export function assetHistoryCoverage(points: ReadonlyArray<{ observation_date: string }>, range: ChartRange): AssetHistoryCoverage | null {
+  if (!Array.isArray(points) || !points.length) return null;
+  const dates = points.map((item) => item?.observation_date).filter((date): date is string => typeof date === "string" && utcDayMs(date) !== null).sort();
+  if (!dates.length) return null;
+  const firstDate = dates[0];
+  const lastDate = dates[dates.length - 1];
+  const days = Math.round((utcDayMs(lastDate)! - utcDayMs(firstDate)!) / 86400000) + 1;
+  const shorterThanRange = range === "all" ? true : days < CHART_RANGE_DAYS[range];
+  return { firstDate, lastDate, days, shorterThanRange };
+}
+
 export type AssetChartGeometry = {
   width: number;
   height: number;