diff --git a/MAINTENANCE.md b/MAINTENANCE.md
index 8217b7d..fbf9b43 100644
--- a/MAINTENANCE.md
+++ b/MAINTENANCE.md
@@ -232,6 +232,7 @@ git push
 10. **Gitea Actions 的 Secrets 改完不会自动触发流水线**——必须手动 re-run，或者推一个新 commit。
 11. **农历 `lunarInfo` 数据表来源要可信**。早期版本数据有错位（多个年份的闰月信息错），导致 solarToLunar 算的春节日期跟实际差 1-2 个月。已替换为权威源 `github.com/jjonline/calendar.js` 的版本。如未来要扩展年份范围（>2100），务必同样从该源取。
 12. **农历存字段必须含 `isLeapMonth`**。只存 `lunarMonth`/`lunarDay` 会丢闰月信息，闰月生日的人每年被错误提醒到普通月份。修复需同时改：数据库列、后端 FIELDS、前端 formData、`lunar.lunarToSolar` 第 4 参数透传。
+13. **`solarToLunar` 月循环必须保留 `temp` 变量**。早期版本在闰月分支里 `offset -= leapDays`、非闰分支 `offset -= monthDays`，循环外的 `if (offset < 0)` 又根据 isLeap 重新判断要加哪个——闰月期间的"非初一日期"会被错算到下一个普通月（例如「闰二月初二」算成「三月初二」）。权威实现（jjonline/calendar.js）让循环内统一 `offset -= temp` 并把 `temp` 保留到循环外用，是更稳的写法。修改算法时一定要用 *闰月连续日期*（如 2023-03-22 到 2023-04-19）做端到端验证，不能只测闰月初一。
 
 ## 与其他记忆的关系
 
diff --git a/server/src/lunar.js b/server/src/lunar.js
index cd86e11..bd771a5 100644
--- a/server/src/lunar.js
+++ b/server/src/lunar.js
@@ -74,62 +74,69 @@ function _monthDays(year, month) {
 
 /**
  * 公历转农历
+ * 算法移植自 github.com/jjonline/calendar.js（权威），与本地原版的差异在月循环退出时
+ * 必须保留 temp 保存最后一次月份天数，否则闰月非初一的日期会被错误地归到下一个普通月份。
  * @param {Date} solarDate
  * @returns {{ year, month, day, isLeap, lunarText }}
  */
 function solarToLunar(solarDate) {
-  const date = new Date(solarDate.getFullYear(), solarDate.getMonth(), solarDate.getDate())
-  let offset = Math.round((date - BASE_DATE) / 86400000)
+  const y = solarDate.getFullYear()
+  const m = solarDate.getMonth() + 1
+  const d = solarDate.getDate()
 
-  let lunarYear, lunarMonth, lunarDay
+  let offset = (Date.UTC(y, m - 1, d) - Date.UTC(1900, 0, 31)) / 86400000
+  let i, leap = 0, temp = 0
+
+  for (i = 1900; i < 2101 && offset > 0; i++) {
+    temp = _lunarYearDays(i)
+    offset -= temp
+  }
+  if (offset < 0) {
+    offset += temp
+    i--
+  }
+
+  const year = i
+  leap = _leapMonth(i)
   let isLeap = false
 
-  for (lunarYear = 1900; lunarYear < 2100 && offset > 0; lunarYear++) {
-    const days = _lunarYearDays(lunarYear)
-    offset -= days
-  }
-  if (offset < 0) {
-    offset += _lunarYearDays(--lunarYear)
-  }
-
-  const leapM = _leapMonth(lunarYear)
-  let isLeapYear = false
-
-  for (lunarMonth = 1; lunarMonth < 13 && offset > 0; lunarMonth++) {
-    if (leapM > 0 && lunarMonth === leapM + 1 && !isLeapYear) {
-      --lunarMonth
-      isLeapYear = true
-      const leapDays = _leapDays(lunarYear)
-      offset -= leapDays
+  for (i = 1; i < 13 && offset > 0; i++) {
+    if (leap > 0 && i === (leap + 1) && isLeap === false) {
+      --i
+      isLeap = true
+      temp = _leapDays(year)
     } else {
-      offset -= _monthDays(lunarYear, lunarMonth)
+      temp = _monthDays(year, i)
     }
-    if (isLeapYear && lunarMonth === leapM + 1) isLeapYear = false
+    if (isLeap === true && i === (leap + 1)) {
+      isLeap = false
+    }
+    offset -= temp
   }
 
-  if (offset === 0 && leapM > 0 && lunarMonth === leapM + 1) {
-    if (isLeapYear) {
-      isLeapYear = false
+  // 闰月下标重叠导致 offset 恰好为 0 时的取反
+  if (offset === 0 && leap > 0 && i === leap + 1) {
+    if (isLeap) {
+      isLeap = false
     } else {
-      isLeapYear = true
-      --lunarMonth
+      isLeap = true
+      --i
     }
   }
   if (offset < 0) {
-    offset += isLeapYear ? _leapDays(lunarYear) : _monthDays(lunarYear, lunarMonth)
-    if (isLeapYear) isLeapYear = false
-    else --lunarMonth
+    offset += temp
+    --i
   }
 
-  lunarDay = offset + 1
-  isLeap = isLeapYear
+  const month = i
+  const day = offset + 1
 
   return {
-    year: lunarYear,
-    month: lunarMonth,
-    day: lunarDay,
+    year,
+    month,
+    day,
     isLeap,
-    lunarText: `${isLeap ? '闰' : ''}${getLunarMonthName(lunarMonth)}月${getLunarDayName(lunarDay)}`
+    lunarText: `${isLeap ? '闰' : ''}${getLunarMonthName(month)}月${getLunarDayName(day)}`
   }
 }
 
diff --git a/utils/lunar.js b/utils/lunar.js
index cd86e11..bd771a5 100644
--- a/utils/lunar.js
+++ b/utils/lunar.js
@@ -74,62 +74,69 @@ function _monthDays(year, month) {
 
 /**
  * 公历转农历
+ * 算法移植自 github.com/jjonline/calendar.js（权威），与本地原版的差异在月循环退出时
+ * 必须保留 temp 保存最后一次月份天数，否则闰月非初一的日期会被错误地归到下一个普通月份。
  * @param {Date} solarDate
  * @returns {{ year, month, day, isLeap, lunarText }}
  */
 function solarToLunar(solarDate) {
-  const date = new Date(solarDate.getFullYear(), solarDate.getMonth(), solarDate.getDate())
-  let offset = Math.round((date - BASE_DATE) / 86400000)
+  const y = solarDate.getFullYear()
+  const m = solarDate.getMonth() + 1
+  const d = solarDate.getDate()
 
-  let lunarYear, lunarMonth, lunarDay
+  let offset = (Date.UTC(y, m - 1, d) - Date.UTC(1900, 0, 31)) / 86400000
+  let i, leap = 0, temp = 0
+
+  for (i = 1900; i < 2101 && offset > 0; i++) {
+    temp = _lunarYearDays(i)
+    offset -= temp
+  }
+  if (offset < 0) {
+    offset += temp
+    i--
+  }
+
+  const year = i
+  leap = _leapMonth(i)
   let isLeap = false
 
-  for (lunarYear = 1900; lunarYear < 2100 && offset > 0; lunarYear++) {
-    const days = _lunarYearDays(lunarYear)
-    offset -= days
-  }
-  if (offset < 0) {
-    offset += _lunarYearDays(--lunarYear)
-  }
-
-  const leapM = _leapMonth(lunarYear)
-  let isLeapYear = false
-
-  for (lunarMonth = 1; lunarMonth < 13 && offset > 0; lunarMonth++) {
-    if (leapM > 0 && lunarMonth === leapM + 1 && !isLeapYear) {
-      --lunarMonth
-      isLeapYear = true
-      const leapDays = _leapDays(lunarYear)
-      offset -= leapDays
+  for (i = 1; i < 13 && offset > 0; i++) {
+    if (leap > 0 && i === (leap + 1) && isLeap === false) {
+      --i
+      isLeap = true
+      temp = _leapDays(year)
     } else {
-      offset -= _monthDays(lunarYear, lunarMonth)
+      temp = _monthDays(year, i)
     }
-    if (isLeapYear && lunarMonth === leapM + 1) isLeapYear = false
+    if (isLeap === true && i === (leap + 1)) {
+      isLeap = false
+    }
+    offset -= temp
   }
 
-  if (offset === 0 && leapM > 0 && lunarMonth === leapM + 1) {
-    if (isLeapYear) {
-      isLeapYear = false
+  // 闰月下标重叠导致 offset 恰好为 0 时的取反
+  if (offset === 0 && leap > 0 && i === leap + 1) {
+    if (isLeap) {
+      isLeap = false
     } else {
-      isLeapYear = true
-      --lunarMonth
+      isLeap = true
+      --i
     }
   }
   if (offset < 0) {
-    offset += isLeapYear ? _leapDays(lunarYear) : _monthDays(lunarYear, lunarMonth)
-    if (isLeapYear) isLeapYear = false
-    else --lunarMonth
+    offset += temp
+    --i
   }
 
-  lunarDay = offset + 1
-  isLeap = isLeapYear
+  const month = i
+  const day = offset + 1
 
   return {
-    year: lunarYear,
-    month: lunarMonth,
-    day: lunarDay,
+    year,
+    month,
+    day,
     isLeap,
-    lunarText: `${isLeap ? '闰' : ''}${getLunarMonthName(lunarMonth)}月${getLunarDayName(lunarDay)}`
+    lunarText: `${isLeap ? '闰' : ''}${getLunarMonthName(month)}月${getLunarDayName(day)}`
   }
 }