diff --git a/src/Backend/SolutionErp.Api/Program.cs b/src/Backend/SolutionErp.Api/Program.cs
index 68b7116..06728a4 100644
--- a/src/Backend/SolutionErp.Api/Program.cs
+++ b/src/Backend/SolutionErp.Api/Program.cs
@@ -27,7 +27,11 @@ builder.Host.UseSerilog((ctx, cfg) => cfg
     .Enrich.FromLogContext());
 
 // ---------- Core services ----------
-builder.Services.AddControllers();
+// [S85 anh Kiệt — TZ FIX] Serialize DateTime UTC-with-Z. EF đọc datetime2 = Unspecified kind →
+// default thiếu 'Z' → FE new Date(naive) hiểu là local → lệch +7h ("mới tạo báo 7h trước").
+// UtcDateTimeJsonConverter ép 'Z' cho MỌI timestamp API → FE convert đúng về giờ local.
+builder.Services.AddControllers().AddJsonOptions(o =>
+    o.JsonSerializerOptions.Converters.Add(new SolutionErp.Api.Serialization.UtcDateTimeJsonConverter()));
 builder.Services.AddSignalR();
 builder.Services.AddSingleton<IRealtimeNotifier, SignalRNotifier>();
 builder.Services.AddHttpContextAccessor();
diff --git a/src/Backend/SolutionErp.Api/Serialization/UtcDateTimeJsonConverter.cs b/src/Backend/SolutionErp.Api/Serialization/UtcDateTimeJsonConverter.cs
new file mode 100644
index 0000000..8bebae6
--- /dev/null
+++ b/src/Backend/SolutionErp.Api/Serialization/UtcDateTimeJsonConverter.cs
@@ -0,0 +1,27 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace SolutionErp.Api.Serialization;
+
+// [S85 anh Kiet — TZ FIX] Timestamps luu UTC (DateTime.UtcNow) nhung EF doc tu SQL Server
+// datetime2 = DateTimeKind.Unspecified -> System.Text.Json mac dinh serialize KHONG co 'Z'
+// (vd "2026-06-23T08:20:00") -> FE new Date(naive) hieu la LOCAL -> lech +7h (VN UTC+7,
+// "moi tao ma bao 7h truoc"). Converter nay ep serialize UTC ISO-8601 CO 'Z' -> FE new
+// Date("...Z") convert dung ve local. System.Text.Json tu dung converter nay cho non-null
+// value cua DateTime? (Nullable) nen khong can dang ky rieng cho DateTime?.
+public sealed class UtcDateTimeJsonConverter : JsonConverter<DateTime>
+{
+    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => reader.GetDateTime();
+
+    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
+    {
+        var utc = value.Kind switch
+        {
+            DateTimeKind.Utc => value,
+            DateTimeKind.Local => value.ToUniversalTime(),
+            _ => DateTime.SpecifyKind(value, DateTimeKind.Utc), // Unspecified (tu EF) = coi la UTC
+        };
+        writer.WriteStringValue(utc.ToString("O")); // ISO-8601 round-trip, co 'Z'
+    }
+}