diff --git a/database/migrations/2026_06_29_100000_activities_start_end_as_date.php b/database/migrations/2026_06_29_100000_activities_start_end_as_date.php
index 8668997..ee9bc92 100644
--- a/database/migrations/2026_06_29_100000_activities_start_end_as_date.php
+++ b/database/migrations/2026_06_29_100000_activities_start_end_as_date.php
@@ -18,11 +18,13 @@ return new class extends Migration
         DB::statement('ALTER TABLE activities ADD COLUMN start_at_date DATE NULL AFTER start_at');
         DB::statement('ALTER TABLE activities ADD COLUMN end_at_date DATE NULL AFTER end_at');
 
+        // TIMESTAMP 在 session 时区下读出已是本地时间，不可再 CONVERT_TZ 从 UTC 加偏移（end_at 23:59:59 会 +1 天）。
+        // 旧数据由 Laravel 按 UTC 写入，用 UTC 字符串显式转换。
         DB::statement(
-            "UPDATE activities SET start_at_date = DATE(CONVERT_TZ(start_at, '+00:00', '{$offset}')) WHERE start_at IS NOT NULL"
+            "UPDATE activities SET start_at_date = DATE(CONVERT_TZ(DATE_FORMAT(start_at, '%Y-%m-%d %H:%i:%s'), '+00:00', '{$offset}')) WHERE start_at IS NOT NULL"
         );
         DB::statement(
-            "UPDATE activities SET end_at_date = DATE(CONVERT_TZ(end_at, '+00:00', '{$offset}')) WHERE end_at IS NOT NULL"
+            "UPDATE activities SET end_at_date = DATE(CONVERT_TZ(DATE_FORMAT(end_at, '%Y-%m-%d %H:%i:%s'), '+00:00', '{$offset}')) WHERE end_at IS NOT NULL"
         );
 
         DB::statement('ALTER TABLE activities DROP COLUMN start_at, DROP COLUMN end_at');
diff --git a/database/migrations/2026_06_29_120000_fix_activities_end_at_off_by_one.php b/database/migrations/2026_06_29_120000_fix_activities_end_at_off_by_one.php
new file mode 100644
index 0000000..7d98fe2
--- /dev/null
+++ b/database/migrations/2026_06_29_120000_fix_activities_end_at_off_by_one.php
@@ -0,0 +1,44 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+/**
+ * 修复 timestamp→date 迁移时 end_at 普遍多 1 天的问题。
+ *
+ * 原因：旧数据 end_at 为东八区当日 23:59:59（UTC 约 15:59:59）。
+ * MySQL 在 session 时区 +08:00 下读取 TIMESTAMP 已是本地 23:59:59，
+ * 再 CONVERT_TZ(..., '+00:00', '+08:00') 会被当作 UTC 再加 8 小时，日历日 +1。
+ * start_at 为 00:00:00 不受影响；仅 end_at 需回退 1 天。
+ */
+return new class extends Migration
+{
+    public function up(): void
+    {
+        if (! Schema::hasTable('activities')) {
+            return;
+        }
+
+        $column = DB::selectOne("SHOW COLUMNS FROM activities WHERE Field = 'end_at'");
+        if (! $column || stripos((string) $column->Type, 'date') === false) {
+            return;
+        }
+
+        DB::statement('UPDATE activities SET end_at = DATE_SUB(end_at, INTERVAL 1 DAY) WHERE end_at IS NOT NULL');
+    }
+
+    public function down(): void
+    {
+        if (! Schema::hasTable('activities')) {
+            return;
+        }
+
+        $column = DB::selectOne("SHOW COLUMNS FROM activities WHERE Field = 'end_at'");
+        if (! $column || stripos((string) $column->Type, 'date') === false) {
+            return;
+        }
+
+        DB::statement('UPDATE activities SET end_at = DATE_ADD(end_at, INTERVAL 1 DAY) WHERE end_at IS NOT NULL');
+    }
+};