diff --git a/document/development/2026-07-18/dev-logs/bugs/employee-age-birthdate-conversion.md b/document/development/2026-07-18/dev-logs/bugs/employee-age-birthdate-conversion.md
new file mode 100644
index 0000000..ec12c7b
--- /dev/null
+++ b/document/development/2026-07-18/dev-logs/bugs/employee-age-birthdate-conversion.md
@@ -0,0 +1,18 @@
+# 员工年龄反算出生日期偏差一年
+
+日期：2026-07-18
+文档路径：document/development/2026-07-18/dev-logs/bugs/employee-age-birthdate-conversion.md
+
+## 修复记录
+
+- 15:40：记录 bug 修复：员工生日在当年尚未到来时，编辑年龄会反算出少一年的年龄。
+  - Git 提交检查：`git fetch --all --prune` 成功；upstream `origin/main` 无新提交；本地 ahead 19 条，最新包括 `07241b46 fix(docker): manage local postgres in default compose`、`787bc3a4 feat(platform): close AI expense value loop`、`242d68c3 feat(approval): add task workflow and waiver decisions`，另有 16 条。
+  - 修改：`employeeManagementModel.js` 在目标生日尚未到来时向前校正出生年份，并为年龄与出生日期转换函数增加可注入的参考日期；新增 `employee-management-age.test.mjs` 覆盖未过生日和已过生日两个边界。
+  - 操作：在 `local-x-financial-linux` 容器内运行员工年龄、员工历史和规则权限定向测试，并执行 Vite 生产构建与 `git diff --check`。
+  - 验证：以 2026-07-18 为参考日期，30 岁且生日为 12 月 31 日时正确生成 `1995-12-31`，回算年龄仍为 30；定向前端测试 9 项全部通过，前端全量测试 `820/820` 通过，Vite 生产构建成功，差异格式检查通过。
+  - 影响：员工管理中直接修改年龄后，保存与重新加载不再把员工年龄静默减一岁。
+- 16:03：补齐 0 岁与闰日出生日期边界。
+  - Git 提交检查：沿用本轮 15:54 拉取检查；upstream `origin/main` 无新提交，本地 ahead 19 条。
+  - 修改：出生年按参考日中生日是否已过推导；0 岁且生日未到时使用上一出生年度，避免生成未来日期；2 月 29 日跨非闰年统一按 2 月 28 日计算和保存。
+  - 验证：参考日 2026-07-18、0 岁、保留 12 月 31 日时生成 `2025-12-31` 并回算 0 岁；闰日跨到非闰年生成合法 `2001-02-28` 并回算 23 岁；定向测试 22 项、前端全量测试 `823/823`、生产构建均通过。
+  - 影响：新生儿档案和闰日生日员工的编辑结果保持合法、可保存且年龄一致。
diff --git a/web/src/views/scripts/employeeManagementModel.js b/web/src/views/scripts/employeeManagementModel.js
index 48a3529..f49e180 100644
--- a/web/src/views/scripts/employeeManagementModel.js
+++ b/web/src/views/scripts/employeeManagementModel.js
@@ -303,21 +303,34 @@ export function resolveOrganizationOptions(metaOrganizations) {
     .sort((a, b) => a.name.localeCompare(b.name, 'zh-CN'))
 }
 
-export function calculateAgeFromDate(dateString) {
-  if (!dateString) {
+export function calculateAgeFromDate(dateString, referenceDate = new Date()) {
+  if (!isValidIsoDate(dateString) || !isValidReferenceDate(referenceDate)) {
     return ''
   }
 
-  const birthDate = new Date(`${dateString}T00:00:00`)
-  if (Number.isNaN(birthDate.getTime())) {
+  const [birthYearText, birthMonthText, birthDayText] = dateString.split('-')
+  const birthYear = Number.parseInt(birthYearText, 10)
+  const birthMonth = Number.parseInt(birthMonthText, 10)
+  const birthDay = Number.parseInt(birthDayText, 10)
+  const referenceYear = referenceDate.getFullYear()
+  const referenceMonth = referenceDate.getMonth() + 1
+  const referenceDay = referenceDate.getDate()
+  const referenceDateNumber = referenceYear * 10000 + referenceMonth * 100 + referenceDay
+  const birthDateNumber = birthYear * 10000 + birthMonth * 100 + birthDay
+
+  if (birthDateNumber > referenceDateNumber) {
     return ''
   }
 
-  const today = new Date()
-  let age = today.getFullYear() - birthDate.getFullYear()
+  const [birthdayMonth, birthdayDay] = normalizeBirthdayForYear(
+    birthMonth,
+    birthDay,
+    referenceYear
+  )
+  let age = referenceYear - birthYear
   const hasBirthdayPassed =
-    today.getMonth() > birthDate.getMonth() ||
-    (today.getMonth() === birthDate.getMonth() && today.getDate() >= birthDate.getDate())
+    referenceMonth > birthdayMonth ||
+    (referenceMonth === birthdayMonth && referenceDay >= birthdayDay)
 
   if (!hasBirthdayPassed) {
     age -= 1
@@ -326,31 +339,56 @@ export function calculateAgeFromDate(dateString) {
   return age >= 0 ? String(age) : ''
 }
 
-export function calculateBirthDateFromAge(ageValue, existingBirthDate = '') {
+export function calculateBirthDateFromAge(
+  ageValue,
+  existingBirthDate = '',
+  referenceDate = new Date()
+) {
   const age = Number.parseInt(String(ageValue ?? '').trim(), 10)
   if (Number.isNaN(age) || age < 0 || age > 120) {
     return existingBirthDate || ''
   }
 
-  const today = new Date()
-  let month = '01'
-  let day = '01'
+  if (!isValidReferenceDate(referenceDate)) {
+    return existingBirthDate || ''
+  }
+
+  let month = 1
+  let day = 1
 
   if (existingBirthDate && isValidIsoDate(existingBirthDate)) {
     const [, monthText, dayText] = existingBirthDate.split('-')
-    month = monthText
-    day = dayText
+    month = Number.parseInt(monthText, 10)
+    day = Number.parseInt(dayText, 10)
   }
 
-  let birthYear = today.getFullYear() - age
-  let candidate = `${birthYear}-${month}-${day}`
+  const referenceYear = referenceDate.getFullYear()
+  const referenceMonth = referenceDate.getMonth() + 1
+  const referenceDay = referenceDate.getDate()
+  const [birthdayMonth, birthdayDay] = normalizeBirthdayForYear(month, day, referenceYear)
+  const hasBirthdayPassed =
+    referenceMonth > birthdayMonth ||
+    (referenceMonth === birthdayMonth && referenceDay >= birthdayDay)
+  const birthYear = referenceYear - age - (hasBirthdayPassed ? 0 : 1)
+  const [birthMonth, birthDay] = normalizeBirthdayForYear(month, day, birthYear)
 
-  if (Number(calculateAgeFromDate(candidate)) > age) {
-    birthYear -= 1
-    candidate = `${birthYear}-${month}-${day}`
+  return `${birthYear}-${padDatePart(birthMonth)}-${padDatePart(birthDay)}`
+}
+
+function isLeapYear(year) {
+  return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0)
+}
+
+function isValidReferenceDate(value) {
+  return typeof value?.getTime === 'function' && !Number.isNaN(value.getTime())
+}
+
+function normalizeBirthdayForYear(month, day, year) {
+  if (month === 2 && day === 29 && !isLeapYear(year)) {
+    return [2, 28]
   }
 
-  return candidate
+  return [month, day]
 }
 
 export function matchKeyword(employee, keyword) {
diff --git a/web/tests/employee-management-age.test.mjs b/web/tests/employee-management-age.test.mjs
new file mode 100644
index 0000000..b73d35c
--- /dev/null
+++ b/web/tests/employee-management-age.test.mjs
@@ -0,0 +1,44 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+
+import {
+  calculateAgeFromDate,
+  calculateBirthDateFromAge,
+  isValidIsoDate
+} from '../src/views/scripts/employeeManagementModel.js'
+
+test('根据年龄反算未到生日的出生年份不会少一年', () => {
+  const referenceDate = new Date('2026-07-18T00:00:00')
+  const birthDate = calculateBirthDateFromAge('30', '1990-12-31', referenceDate)
+
+  assert.equal(birthDate, '1995-12-31')
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '30')
+})
+
+test('根据年龄反算已过生日的出生年份保持当年差值', () => {
+  const referenceDate = new Date('2026-07-18T00:00:00')
+  const birthDate = calculateBirthDateFromAge('30', '1990-01-01', referenceDate)
+
+  assert.equal(birthDate, '1996-01-01')
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '30')
+})
+
+test('零岁且生日月日尚未到来时不会生成未来出生日期', () => {
+  const referenceDate = new Date('2026-07-18T00:00:00')
+  const birthDate = calculateBirthDateFromAge('0', '2000-12-31', referenceDate)
+
+  assert.equal(birthDate, '2025-12-31')
+  assert.equal(isValidIsoDate(birthDate), true)
+  assert.equal(new Date(`${birthDate}T00:00:00`) <= referenceDate, true)
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '0')
+})
+
+test('闰日生日跨非闰年时使用二月二十八日并保持年龄回算一致', () => {
+  const referenceDate = new Date('2024-03-01T00:00:00')
+  const birthDate = calculateBirthDateFromAge('23', '2000-02-29', referenceDate)
+
+  assert.equal(birthDate, '2001-02-28')
+  assert.equal(isValidIsoDate(birthDate), true)
+  assert.equal(calculateAgeFromDate(birthDate, referenceDate), '23')
+  assert.equal(calculateAgeFromDate('2000-02-29', new Date('2023-02-28T00:00:00')), '23')
+})