diff --git a/backend/internal/repository/dashboard_aggregation_repo.go b/backend/internal/repository/dashboard_aggregation_repo.go
index dbba5cdb..b02cde0d 100644
--- a/backend/internal/repository/dashboard_aggregation_repo.go
+++ b/backend/internal/repository/dashboard_aggregation_repo.go
@@ -43,10 +43,11 @@ func (r *dashboardAggregationRepository) AggregateRange(ctx context.Context, sta
 		dayEnd = dayEnd.Add(24 * time.Hour)
 	}
 
-	if err := r.insertHourlyActiveUsers(ctx, startUTC, endUTC); err != nil {
+	// 以桶边界聚合，允许覆盖 end 所在桶的剩余区间。
+	if err := r.insertHourlyActiveUsers(ctx, hourStart, hourEnd); err != nil {
 		return err
 	}
-	if err := r.insertDailyActiveUsers(ctx, startUTC, endUTC); err != nil {
+	if err := r.insertDailyActiveUsers(ctx, hourStart, hourEnd); err != nil {
 		return err
 	}
 	if err := r.upsertHourlyAggregates(ctx, hourStart, hourEnd); err != nil {
@@ -138,10 +139,10 @@ func (r *dashboardAggregationRepository) insertDailyActiveUsers(ctx context.Cont
 	query := `
 		INSERT INTO usage_dashboard_daily_users (bucket_date, user_id)
 		SELECT DISTINCT
-			(created_at AT TIME ZONE 'UTC')::date AS bucket_date,
+			(bucket_start AT TIME ZONE 'UTC')::date AS bucket_date,
 			user_id
-		FROM usage_logs
-		WHERE created_at >= $1 AND created_at < $2
+		FROM usage_dashboard_hourly_users
+		WHERE bucket_start >= $1 AND bucket_start < $2
 		ON CONFLICT DO NOTHING
 	`
 	_, err := r.sql.ExecContext(ctx, query, start.UTC(), end.UTC())
diff --git a/backend/internal/service/dashboard_aggregation_service.go b/backend/internal/service/dashboard_aggregation_service.go
index 343c3240..133ab018 100644
--- a/backend/internal/service/dashboard_aggregation_service.go
+++ b/backend/internal/service/dashboard_aggregation_service.go
@@ -134,12 +134,12 @@ func (s *DashboardAggregationService) runScheduledAggregation() {
 	}
 
 	lookback := time.Duration(s.cfg.LookbackSeconds) * time.Second
-	start := last.Add(-lookback)
 	epoch := time.Unix(0, 0).UTC()
+	start := last.Add(-lookback)
 	if !last.After(epoch) {
-		start = now.Add(-lookback)
-	}
-	if start.After(now) {
+		// 首次聚合覆盖当天，避免只统计最后一个窗口。
+		start = truncateToDayUTC(now)
+	} else if start.After(now) {
 		start = now.Add(-lookback)
 	}
 
@@ -204,17 +204,21 @@ func (s *DashboardAggregationService) maybeCleanupRetention(ctx context.Context,
 			return
 		}
 	}
-	s.lastRetentionCleanup.Store(now)
 
 	hourlyCutoff := now.AddDate(0, 0, -s.cfg.Retention.HourlyDays)
 	dailyCutoff := now.AddDate(0, 0, -s.cfg.Retention.DailyDays)
 	usageCutoff := now.AddDate(0, 0, -s.cfg.Retention.UsageLogsDays)
 
-	if err := s.repo.CleanupAggregates(ctx, hourlyCutoff, dailyCutoff); err != nil {
-		log.Printf("[DashboardAggregation] 聚合保留清理失败: %v", err)
+	aggErr := s.repo.CleanupAggregates(ctx, hourlyCutoff, dailyCutoff)
+	if aggErr != nil {
+		log.Printf("[DashboardAggregation] 聚合保留清理失败: %v", aggErr)
 	}
-	if err := s.repo.CleanupUsageLogs(ctx, usageCutoff); err != nil {
-		log.Printf("[DashboardAggregation] usage_logs 保留清理失败: %v", err)
+	usageErr := s.repo.CleanupUsageLogs(ctx, usageCutoff)
+	if usageErr != nil {
+		log.Printf("[DashboardAggregation] usage_logs 保留清理失败: %v", usageErr)
+	}
+	if aggErr == nil && usageErr == nil {
+		s.lastRetentionCleanup.Store(now)
 	}
 }
 
diff --git a/backend/internal/service/dashboard_aggregation_service_test.go b/backend/internal/service/dashboard_aggregation_service_test.go
new file mode 100644
index 00000000..501b11d4
--- /dev/null
+++ b/backend/internal/service/dashboard_aggregation_service_test.go
@@ -0,0 +1,89 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/stretchr/testify/require"
+)
+
+type dashboardAggregationRepoTestStub struct {
+	aggregateCalls       int
+	lastStart            time.Time
+	lastEnd              time.Time
+	watermark            time.Time
+	aggregateErr         error
+	cleanupAggregatesErr error
+	cleanupUsageErr      error
+}
+
+func (s *dashboardAggregationRepoTestStub) AggregateRange(ctx context.Context, start, end time.Time) error {
+	s.aggregateCalls++
+	s.lastStart = start
+	s.lastEnd = end
+	return s.aggregateErr
+}
+
+func (s *dashboardAggregationRepoTestStub) GetAggregationWatermark(ctx context.Context) (time.Time, error) {
+	return s.watermark, nil
+}
+
+func (s *dashboardAggregationRepoTestStub) UpdateAggregationWatermark(ctx context.Context, aggregatedAt time.Time) error {
+	return nil
+}
+
+func (s *dashboardAggregationRepoTestStub) CleanupAggregates(ctx context.Context, hourlyCutoff, dailyCutoff time.Time) error {
+	return s.cleanupAggregatesErr
+}
+
+func (s *dashboardAggregationRepoTestStub) CleanupUsageLogs(ctx context.Context, cutoff time.Time) error {
+	return s.cleanupUsageErr
+}
+
+func (s *dashboardAggregationRepoTestStub) EnsureUsageLogsPartitions(ctx context.Context, now time.Time) error {
+	return nil
+}
+
+func TestDashboardAggregationService_RunScheduledAggregation_EpochUsesDayStart(t *testing.T) {
+	repo := &dashboardAggregationRepoTestStub{watermark: time.Unix(0, 0).UTC()}
+	svc := &DashboardAggregationService{
+		repo: repo,
+		cfg: config.DashboardAggregationConfig{
+			Enabled:         true,
+			IntervalSeconds: 60,
+			LookbackSeconds: 120,
+			Retention: config.DashboardAggregationRetentionConfig{
+				UsageLogsDays: 1,
+				HourlyDays:    1,
+				DailyDays:     1,
+			},
+		},
+	}
+
+	svc.runScheduledAggregation()
+
+	require.Equal(t, 1, repo.aggregateCalls)
+	require.False(t, repo.lastEnd.IsZero())
+	require.Equal(t, truncateToDayUTC(repo.lastEnd), repo.lastStart)
+}
+
+func TestDashboardAggregationService_CleanupRetentionFailure_DoesNotRecord(t *testing.T) {
+	repo := &dashboardAggregationRepoTestStub{cleanupAggregatesErr: errors.New("清理失败")}
+	svc := &DashboardAggregationService{
+		repo: repo,
+		cfg: config.DashboardAggregationConfig{
+			Retention: config.DashboardAggregationRetentionConfig{
+				UsageLogsDays: 1,
+				HourlyDays:    1,
+				DailyDays:     1,
+			},
+		},
+	}
+
+	svc.maybeCleanupRetention(context.Background(), time.Now().UTC())
+
+	require.Nil(t, svc.lastRetentionCleanup.Load())
+}