diff --git a/backend/internal/service/account.go b/backend/internal/service/account.go
index fb95201f20..de7d97f884 100644
--- a/backend/internal/service/account.go
+++ b/backend/internal/service/account.go
@@ -2036,6 +2036,60 @@ func ComputeQuotaResetAt(extra map[string]any) {
 	}
 }
 
+// NormalizeFixedQuotaWindows aligns preserved quota usage with the active fixed reset window.
+//
+// Editing an existing account can switch a daily/weekly quota from rolling to fixed reset
+// while preserving quota_*_used and quota_*_start. If the preserved start belongs to the
+// old rolling window, response mapping treats the usage as expired and the dashboard shows
+// 0 until the next reset. Normalize those stale starts before persisting the edited account.
+func NormalizeFixedQuotaWindows(extra map[string]any) {
+	if extra == nil {
+		return
+	}
+	now := time.Now()
+	tzName, _ := extra["quota_reset_timezone"].(string)
+	if tzName == "" {
+		tzName = "UTC"
+	}
+	tz, err := time.LoadLocation(tzName)
+	if err != nil {
+		tz = time.UTC
+	}
+
+	if mode, _ := extra["quota_daily_reset_mode"].(string); mode == "fixed" && parseExtraFloat64(extra["quota_daily_limit"]) > 0 {
+		hour := int(parseExtraFloat64(extra["quota_daily_reset_hour"]))
+		if hour < 0 || hour > 23 {
+			hour = 0
+		}
+		lastReset := lastFixedDailyReset(hour, tz, now)
+		start := parseExtraTime(extra["quota_daily_start"])
+		if start.IsZero() || start.Before(lastReset) {
+			extra["quota_daily_used"] = 0.0
+			extra["quota_daily_start"] = lastReset.UTC().Format(time.RFC3339)
+		}
+	}
+
+	if mode, _ := extra["quota_weekly_reset_mode"].(string); mode == "fixed" && parseExtraFloat64(extra["quota_weekly_limit"]) > 0 {
+		day := 1
+		if rawDay, ok := extra["quota_weekly_reset_day"]; ok {
+			day = int(parseExtraFloat64(rawDay))
+		}
+		if day < 0 || day > 6 {
+			day = 1
+		}
+		hour := int(parseExtraFloat64(extra["quota_weekly_reset_hour"]))
+		if hour < 0 || hour > 23 {
+			hour = 0
+		}
+		lastReset := lastFixedWeeklyReset(day, hour, tz, now)
+		start := parseExtraTime(extra["quota_weekly_start"])
+		if start.IsZero() || start.Before(lastReset) {
+			extra["quota_weekly_used"] = 0.0
+			extra["quota_weekly_start"] = lastReset.UTC().Format(time.RFC3339)
+		}
+	}
+}
+
 // ValidateQuotaResetConfig 校验配额固定重置时间配置的合法性
 func ValidateQuotaResetConfig(extra map[string]any) error {
 	if extra == nil {
@@ -2364,6 +2418,18 @@ func parseExtraFloat64(value any) float64 {
 	return 0
 }
 
+func parseExtraTime(value any) time.Time {
+	if s, ok := value.(string); ok {
+		if t, err := time.Parse(time.RFC3339Nano, s); err == nil {
+			return t
+		}
+		if t, err := time.Parse(time.RFC3339, s); err == nil {
+			return t
+		}
+	}
+	return time.Time{}
+}
+
 // parseExtraInt 从 extra 字段解析 int 值
 // ParseExtraInt 从 extra 字段的 any 值解析为 int。
 // 支持 int, int64, float64, json.Number, string 类型，无法解析时返回 0。
diff --git a/backend/internal/service/account_quota_reset_test.go b/backend/internal/service/account_quota_reset_test.go
index 45a4bad6e9..fe0900c04e 100644
--- a/backend/internal/service/account_quota_reset_test.go
+++ b/backend/internal/service/account_quota_reset_test.go
@@ -398,6 +398,51 @@ func TestValidateQuotaResetConfig_BoundaryValues(t *testing.T) {
 	assert.NoError(t, ValidateQuotaResetConfig(extra2))
 }
 
+// ---------------------------------------------------------------------------
+// NormalizeFixedQuotaWindows
+// ---------------------------------------------------------------------------
+
+func TestNormalizeFixedQuotaWindows_ClearsExpiredWeeklyWindow(t *testing.T) {
+	now := time.Now().UTC()
+	daysSinceMonday := (int(now.Weekday()) + 6) % 7
+	currentWeekStart := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, time.UTC).AddDate(0, 0, -daysSinceMonday)
+	staleStart := currentWeekStart.Add(-24 * time.Hour)
+	extra := map[string]any{
+		"quota_weekly_limit":      500.0,
+		"quota_weekly_used":       76.0,
+		"quota_weekly_start":      staleStart.Format(time.RFC3339),
+		"quota_weekly_reset_mode": "fixed",
+		"quota_weekly_reset_day":  float64(1),
+		"quota_weekly_reset_hour": float64(0),
+		"quota_reset_timezone":    "UTC",
+	}
+
+	NormalizeFixedQuotaWindows(extra)
+
+	assert.Equal(t, 0.0, extra["quota_weekly_used"])
+	assert.Equal(t, currentWeekStart.Format(time.RFC3339), extra["quota_weekly_start"])
+}
+
+func TestNormalizeFixedQuotaWindows_KeepsActiveWeeklyWindow(t *testing.T) {
+	now := time.Now().UTC()
+	daysSinceMonday := (int(now.Weekday()) + 6) % 7
+	currentWeekStart := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, time.UTC).AddDate(0, 0, -daysSinceMonday)
+	extra := map[string]any{
+		"quota_weekly_limit":      500.0,
+		"quota_weekly_used":       76.0,
+		"quota_weekly_start":      currentWeekStart.Format(time.RFC3339),
+		"quota_weekly_reset_mode": "fixed",
+		"quota_weekly_reset_day":  float64(1),
+		"quota_weekly_reset_hour": float64(0),
+		"quota_reset_timezone":    "UTC",
+	}
+
+	NormalizeFixedQuotaWindows(extra)
+
+	assert.Equal(t, 76.0, extra["quota_weekly_used"])
+	assert.Equal(t, currentWeekStart.Format(time.RFC3339), extra["quota_weekly_start"])
+}
+
 // ---------------------------------------------------------------------------
 // ComputeQuotaResetAt
 // ---------------------------------------------------------------------------
diff --git a/backend/internal/service/admin_service.go b/backend/internal/service/admin_service.go
index 00205d1f79..562298a1cc 100644
--- a/backend/internal/service/admin_service.go
+++ b/backend/internal/service/admin_service.go
@@ -2498,6 +2498,7 @@ func (s *adminServiceImpl) CreateAccount(ctx context.Context, input *CreateAccou
 			return nil, err
 		}
 		ComputeQuotaResetAt(account.Extra)
+		NormalizeFixedQuotaWindows(account.Extra)
 	}
 	if input.ExpiresAt != nil && *input.ExpiresAt > 0 {
 		expiresAt := time.Unix(*input.ExpiresAt, 0)
@@ -2606,6 +2607,7 @@ func (s *adminServiceImpl) UpdateAccount(ctx context.Context, id int64, input *U
 			return nil, err
 		}
 		ComputeQuotaResetAt(account.Extra)
+		NormalizeFixedQuotaWindows(account.Extra)
 	}
 	if input.ProxyID != nil {
 		// 0 表示清除代理（前端发送 0 而不是 null 来表达清除意图）
diff --git a/backend/internal/service/admin_service_overages_test.go b/backend/internal/service/admin_service_overages_test.go
index d6380f4dcd..211ad4cd7a 100644
--- a/backend/internal/service/admin_service_overages_test.go
+++ b/backend/internal/service/admin_service_overages_test.go
@@ -153,3 +153,42 @@ func TestUpdateAccount_EmptyExtraPayloadCanClearQuotaLimits(t *testing.T) {
 	require.NotContains(t, repo.account.Extra, "quota_weekly_limit")
 	require.Len(t, repo.account.Extra, 0)
 }
+
+func TestUpdateAccount_FixedWeeklyResetClearsLegacyRollingUsage(t *testing.T) {
+	now := time.Now().UTC()
+	daysSinceMonday := (int(now.Weekday()) + 6) % 7
+	currentWeekStart := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, time.UTC).AddDate(0, 0, -daysSinceMonday)
+	legacyRollingStart := currentWeekStart.Add(-24 * time.Hour)
+	accountID := int64(104)
+	repo := &updateAccountOveragesRepoStub{
+		account: &Account{
+			ID:       accountID,
+			Platform: PlatformAnthropic,
+			Type:     AccountTypeAPIKey,
+			Status:   StatusActive,
+			Extra: map[string]any{
+				"quota_weekly_limit": 40.0,
+				"quota_weekly_used":  12.5,
+				"quota_weekly_start": legacyRollingStart.Format(time.RFC3339),
+			},
+		},
+	}
+
+	svc := &adminServiceImpl{accountRepo: repo}
+	updated, err := svc.UpdateAccount(context.Background(), accountID, &UpdateAccountInput{
+		Extra: map[string]any{
+			"quota_weekly_limit":      40.0,
+			"quota_weekly_reset_mode": "fixed",
+			"quota_weekly_reset_day":  float64(1),
+			"quota_weekly_reset_hour": float64(0),
+			"quota_reset_timezone":    "UTC",
+		},
+	})
+
+	require.NoError(t, err)
+	require.NotNil(t, updated)
+	require.Equal(t, 1, repo.updateCalls)
+	require.InDelta(t, 0.0, updated.GetQuotaWeeklyUsed(), 1e-9)
+	require.Equal(t, currentWeekStart.Format(time.RFC3339), updated.Extra["quota_weekly_start"])
+	require.False(t, updated.IsWeeklyQuotaPeriodExpired())
+}