diff --git a/src/elder/elder.service.spec.ts b/src/elder/elder.service.spec.ts
index b33cac7..2dcff78 100644
--- a/src/elder/elder.service.spec.ts
+++ b/src/elder/elder.service.spec.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it, vi } from 'vitest';
-import { ElderService, maskIdCard } from './elder.service.js';
+import { ElderService, maskIdCard, toDateOnly } from './elder.service.js';
 import type { PrismaService } from '../prisma/prisma.service.js';
 import type { StorageService } from '../storage/storage.service.js';
 import type { AuditLogsService } from '../audit-logs/audit-logs.service.js';
@@ -109,6 +109,18 @@ describe('maskIdCard', () => {
   });
 });
 
+describe('toDateOnly', () => {
+  it('date-only 字符串 → UTC 零点 Date（不提前一天）', () => {
+    expect(toDateOnly('1990-01-01')?.toISOString()).toBe('1990-01-01T00:00:00.000Z');
+    expect(toDateOnly('2025-01-01')?.toISOString()).toBe('2025-01-01T00:00:00.000Z');
+  });
+
+  it('空值返回 undefined', () => {
+    expect(toDateOnly(undefined)).toBeUndefined();
+    expect(toDateOnly('')).toBeUndefined();
+  });
+});
+
 describe('ElderService', () => {
   it('create 有等级无评估结论副本 → 抛 ELDER_LEVEL_REQUIRES_EVIDENCE', async () => {
     const { service, elderCreate } = makeService();
@@ -144,7 +156,7 @@ describe('ElderService', () => {
     });
   });
 
-  it('合法建档（含日期字段）成功创建，日期字段转为 Date', async () => {
+  it('合法建档（含日期字段）成功创建，日期字段转为 UTC 零点 Date 且值正确', async () => {
     const { service, elderCreate } = makeService();
 
     await runWithRequestContext(ctx, () =>
@@ -159,17 +171,15 @@ describe('ElderService', () => {
       }),
     );
 
-    expect(elderCreate).toHaveBeenCalledWith({
-      data: expect.objectContaining({
-        birthDate: expect.any(Date),
-        benefitStart: expect.any(Date),
-        benefitEnd: expect.any(Date),
-        assessDate: expect.any(Date),
-        insurVerifyDate: expect.any(Date),
-        hospStart: expect.any(Date),
-        hospEnd: expect.any(Date),
-      }),
-    });
+    const data = elderCreate.mock.calls[0][0].data as Record<string, unknown>;
+    expect(data.birthDate).toBeInstanceOf(Date);
+    expect((data.birthDate as Date).toISOString()).toBe('1990-01-01T00:00:00.000Z');
+    expect((data.benefitStart as Date).toISOString()).toBe('2025-01-01T00:00:00.000Z');
+    expect((data.benefitEnd as Date).toISOString()).toBe('2025-12-31T00:00:00.000Z');
+    expect((data.assessDate as Date).toISOString()).toBe('2025-01-15T00:00:00.000Z');
+    expect((data.insurVerifyDate as Date).toISOString()).toBe('2025-01-10T00:00:00.000Z');
+    expect((data.hospStart as Date).toISOString()).toBe('2025-02-01T00:00:00.000Z');
+    expect((data.hospEnd as Date).toISOString()).toBe('2025-02-05T00:00:00.000Z');
   });
 
   it('同机构重复 id_card_no → 抛 ELDER_ID_CARD_EXISTS', async () => {
diff --git a/src/elder/elder.service.ts b/src/elder/elder.service.ts
index 39804ea..c21a258 100644
--- a/src/elder/elder.service.ts
+++ b/src/elder/elder.service.ts
@@ -52,10 +52,10 @@ function resolveInitialStatus(benefitStart?: string, benefitEnd?: string): strin
   return 'waiting_period';
 }
 
-/** YYYY-MM-DD → 本地零点 Date（供 Prisma DateTime @db.Date 列写入）；空值返回 undefined。 */
-function toDateOnly(v?: string): Date | undefined {
+/** YYYY-MM-DD → UTC 零点 Date（Prisma @db.Date 按 UTC instant 取日期，须用 UTC 零点避免时区回退一天）；空值返回 undefined。 */
+export function toDateOnly(v?: string): Date | undefined {
   if (!v) return undefined;
-  return new Date(`${v}T00:00:00`);
+  return new Date(`${v}T00:00:00Z`);
 }
 
 /**