diff --git a/backend/internal/repository/channel_monitor_v2_aggregation.go b/backend/internal/repository/channel_monitor_v2_aggregation.go
index 9bec5877b5..eb3d489c6e 100644
--- a/backend/internal/repository/channel_monitor_v2_aggregation.go
+++ b/backend/internal/repository/channel_monitor_v2_aggregation.go
@@ -395,11 +395,21 @@ func sameFixedRollupBucket(start, end time.Time, seconds int) bool {
 	return start.Truncate(interval).Equal(end.Add(-time.Nanosecond).Truncate(interval))
 }
 
+// PostgreSQL interprets a TIMESTAMPTZ literal without an explicit offset in
+// the current session timezone. Keep date_bin's origin fixed in UTC so bucket
+// boundaries do not shift when the database session runs in Asia/Shanghai (or
+// any other non-UTC timezone).
+const channelMonitorV2DateBinOrigin = "TIMESTAMPTZ '1970-01-01 00:00:00+00'"
+
+func channelMonitorV2DateBinExpr(column string) string {
+	return "date_bin($1::interval," + column + "," + channelMonitorV2DateBinOrigin + ")"
+}
+
 const channelMonitorV2FixedRollupBoundsSQL = `
 WITH bounds AS (
   SELECT
-    date_bin($1::interval, $3::timestamptz, TIMESTAMPTZ '1970-01-01') AS start_at,
-    date_bin($1::interval, $4::timestamptz - INTERVAL '1 microsecond', TIMESTAMPTZ '1970-01-01') + $1::interval AS end_at
+    date_bin($1::interval, $3::timestamptz, ` + channelMonitorV2DateBinOrigin + `) AS start_at,
+    date_bin($1::interval, $4::timestamptz - INTERVAL '1 microsecond', ` + channelMonitorV2DateBinOrigin + `) + $1::interval AS end_at
 )`
 
 const channelMonitorV2FixedRollupDeleteSQL = channelMonitorV2FixedRollupBoundsSQL + `
@@ -417,7 +427,7 @@ INSERT INTO channel_monitor_v2_metrics_rollup (
   duration_count, computed_at
 )
 ` + channelMonitorV2FixedRollupBoundsSQL + `
-SELECT date_bin($1::interval, m.bucket_start, TIMESTAMPTZ '1970-01-01'), $2::integer,
+SELECT date_bin($1::interval, m.bucket_start, ` + channelMonitorV2DateBinOrigin + `), $2::integer,
        platform, group_id, model, SUM(success_requests), SUM(error_requests),
        SUM(upstream_affected_requests), SUM(upstream_attempt_count), SUM(input_tokens),
        SUM(output_tokens), SUM(cache_creation_tokens), SUM(cache_read_tokens),
@@ -433,7 +443,7 @@ INSERT INTO channel_monitor_v2_user_metrics_rollup (
   ttft_sum_ms, ttft_count, duration_sum_ms, duration_count, computed_at
 )
 ` + channelMonitorV2FixedRollupBoundsSQL + `
-SELECT date_bin($1::interval, m.bucket_start, TIMESTAMPTZ '1970-01-01'), $2::integer,
+SELECT date_bin($1::interval, m.bucket_start, ` + channelMonitorV2DateBinOrigin + `), $2::integer,
        platform, group_id, model, user_id, SUM(success_requests), SUM(error_requests),
        SUM(input_tokens), SUM(output_tokens), SUM(cache_creation_tokens), SUM(cache_read_tokens),
        SUM(ttft_sum_ms), SUM(ttft_count), SUM(duration_sum_ms), SUM(duration_count), NOW()
@@ -446,7 +456,7 @@ INSERT INTO channel_monitor_v2_latency_histograms_rollup (
   bucket_start, bucket_seconds, platform, group_id, model, user_id, metric, upper_bound_ms, sample_count
 )
 ` + channelMonitorV2FixedRollupBoundsSQL + `
-SELECT date_bin($1::interval, h.bucket_start, TIMESTAMPTZ '1970-01-01'), $2::integer,
+SELECT date_bin($1::interval, h.bucket_start, ` + channelMonitorV2DateBinOrigin + `), $2::integer,
        platform, group_id, model, user_id, metric, upper_bound_ms, SUM(sample_count)
 FROM channel_monitor_v2_latency_histograms_1m h, bounds
 WHERE h.bucket_start >= bounds.start_at AND h.bucket_start < bounds.end_at
@@ -457,7 +467,7 @@ INSERT INTO channel_monitor_v2_error_metrics_rollup (
   bucket_start, bucket_seconds, platform, group_id, model, error_category, taxonomy_version, error_requests
 )
 ` + channelMonitorV2FixedRollupBoundsSQL + `
-SELECT date_bin($1::interval, e.bucket_start, TIMESTAMPTZ '1970-01-01'), $2::integer,
+SELECT date_bin($1::interval, e.bucket_start, ` + channelMonitorV2DateBinOrigin + `), $2::integer,
        platform, group_id, model, error_category, taxonomy_version, SUM(error_requests)
 FROM channel_monitor_v2_error_metrics_1m e, bounds
 WHERE e.bucket_start >= bounds.start_at AND e.bucket_start < bounds.end_at
diff --git a/backend/internal/repository/channel_monitor_v2_repo.go b/backend/internal/repository/channel_monitor_v2_repo.go
index 978fb44bb0..025f4df8f1 100644
--- a/backend/internal/repository/channel_monitor_v2_repo.go
+++ b/backend/internal/repository/channel_monitor_v2_repo.go
@@ -949,7 +949,7 @@ func (r *channelMonitorV2Repository) loadFacts(ctx context.Context, filter servi
 		} else {
 			args = append([]any{fmt.Sprintf("%d seconds", int(filter.Bucket.Seconds()))}, args...)
 			where = shiftSQLPlaceholders(where, 1)
-			bucketExpr = "date_bin($1::interval,m.bucket_start,TIMESTAMPTZ '1970-01-01')"
+			bucketExpr = channelMonitorV2DateBinExpr("m.bucket_start")
 			group = bucketExpr + "," + group
 		}
 	}
@@ -991,7 +991,7 @@ func (r *channelMonitorV2Repository) loadHistograms(ctx context.Context, filter
 			args = []any{fmt.Sprintf("%d seconds", int(filter.Bucket.Seconds()))}
 			args = append(args, oldArgs...)
 			where = shiftSQLPlaceholders(where, 1)
-			bucketExpr = "date_bin($1::interval,h.bucket_start,TIMESTAMPTZ '1970-01-01')"
+			bucketExpr = channelMonitorV2DateBinExpr("h.bucket_start")
 			group = bucketExpr + "," + group
 		}
 	}
@@ -1444,7 +1444,7 @@ func (r *channelMonitorV2Repository) loadIgnoredErrorCounts(
 	if filter.Bucket > 0 && bucketSeconds == 0 {
 		args = append([]any{fmt.Sprintf("%d seconds", int(filter.Bucket.Seconds()))}, args...)
 		where = shiftSQLPlaceholders(where, 1)
-		bucketExpr = "date_bin($1::interval,e.bucket_start,TIMESTAMPTZ '1970-01-01')"
+		bucketExpr = channelMonitorV2DateBinExpr("e.bucket_start")
 		groupBy = bucketExpr + ", e.platform, e.model"
 	}
 	args = append(args, pq.Array(cfg.IgnoredErrorCategories), service.ChannelMonitorV2TaxonomyVersion)
@@ -1540,7 +1540,7 @@ func (r *channelMonitorV2Repository) loadIgnoredErrorCountsByMatrixKey(
 	if filter.Bucket > 0 && bucketSeconds == 0 {
 		args = append([]any{fmt.Sprintf("%d seconds", int(filter.Bucket.Seconds()))}, args...)
 		where = shiftSQLPlaceholders(where, 1)
-		bucketExpr = "date_bin($1::interval,e.bucket_start,TIMESTAMPTZ '1970-01-01')"
+		bucketExpr = channelMonitorV2DateBinExpr("e.bucket_start")
 		groupSQL = bucketExpr + ", e.platform, e.group_id, e.model"
 	}
 	args = append(args, pq.Array(cfg.IgnoredErrorCategories), service.ChannelMonitorV2TaxonomyVersion)
diff --git a/backend/internal/repository/channel_monitor_v2_repo_test.go b/backend/internal/repository/channel_monitor_v2_repo_test.go
index c6cec9c926..ac3ae7317c 100644
--- a/backend/internal/repository/channel_monitor_v2_repo_test.go
+++ b/backend/internal/repository/channel_monitor_v2_repo_test.go
@@ -12,6 +12,22 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestChannelMonitorV2DateBinOriginIsUTC(t *testing.T) {
+	require.Equal(t, "TIMESTAMPTZ '1970-01-01 00:00:00+00'", channelMonitorV2DateBinOrigin)
+	require.Equal(t, "date_bin($1::interval,m.bucket_start,TIMESTAMPTZ '1970-01-01 00:00:00+00')", channelMonitorV2DateBinExpr("m.bucket_start"))
+
+	for _, query := range []string{
+		channelMonitorV2FixedRollupBoundsSQL,
+		channelMonitorV2MetricsRollupSQL,
+		channelMonitorV2UserMetricsRollupSQL,
+		channelMonitorV2HistogramRollupSQL,
+		channelMonitorV2ErrorRollupSQL,
+	} {
+		require.Contains(t, query, channelMonitorV2DateBinOrigin)
+		require.NotContains(t, query, "TIMESTAMPTZ '1970-01-01'")
+	}
+}
+
 func TestChannelMonitorV2DisplayModelIsPlatformScoped(t *testing.T) {
 	cfg := service.ChannelMonitorV2Config{Platforms: []service.ChannelMonitorV2PlatformConfig{
 		{Platform: "openai", Enabled: true, Models: []string{"shared", "gpt-5"}},