📅 递减日历日期Decrement Calendar Date
把每行日期减去若干天、月或年（可批量，月末自动对齐）。本地处理。可设置「数量」、「单位」。Subtract days, months or years from each date (batch; month ends are clamped). Processed locally. Settings: Amount, Unit.
使用说明与常见问题How-to & FAQ
「递减日历日期」是什么？What is the Decrement Calendar Date tool?
把每行日期减去若干天、月或年（可批量，月末自动对齐）。本地处理。可设置「数量」、「单位」。Subtract days, months or years from each date (batch; month ends are clamped). Processed locally. Settings: Amount, Unit.
如何使用「递减日历日期」？How do I use the Decrement Calendar Date tool?
每行输入一个 YYYY-MM-DD 日期，填写“数量”并选择单位（天、月或年），下方即显示减去之后的日期。Enter one YYYY-MM-DD date per line, fill in Amount and pick a unit (days, months or years); the earlier dates appear below.
可以减月或减年吗？Can I subtract months or years?
可以，在“单位”里选择天、月或年。减月/减年时如果目标月份没有那一天，就取该月最后一天，例如 2024-03-31 减 1 个月 = 2024-02-29。Yes, choose days, months or years under Unit. When the target month is too short for the day, the last day of that month is used; for example 2024-03-31 minus 1 month is 2024-02-29.
可以一次处理很多日期吗？Can I process many dates at once?
可以，每行一个 YYYY-MM-DD 日期，空行会跳过；几千行也能即时完成。格式不对时会指出是第几行。Yes. Put one YYYY-MM-DD date on each line; blank lines are skipped and thousands of lines finish instantly. An invalid line is reported with its line number.
“数量”留空会怎样？What if Amount is left empty?
留空时按 1 计算；数量须为非负整数，1e1、0x10 这类写法会报错。An empty Amount counts as 1. It must be a whole number of 0 or more; forms like 1e1 or 0x10 give an error.
用的是哪种历法？Which calendar is used?
公历日期按外推格里高利历（把现行公历规则一直向前沿用）计算，年份范围 0001–9999；1582-10-05 至 1582-10-14 在 1582 年改历的国家并不存在，遇到时会提示。Gregorian dates use the proleptic Gregorian calendar (today's rules applied backwards) for years 0001 to 9999. The days 1582-10-05 to 1582-10-14 never happened in countries that switched in 1582, and the tool shows a note when you use them.
这个工具和时区有关吗？Do time zones affect this tool?
无关。这里只做纯日历或数字运算，不读取设备时钟，也不使用任何时区，所以在哪里打开结果都一样。No. It does pure calendar or number arithmetic, never reads your device clock and uses no time zone, so the result is the same wherever you open the page.
输入和输出是什么样的？What does the input and output look like?
例如把「数量」设为 1，输入 2020-01-15，输出为：2020-01-14。With "Amount" set to 1, the input 2020-01-15 becomes 2020-01-14.
有哪些选项可以调整？What options can I adjust?
「递减日历日期」的设置：「数量」默认 1；「单位」可选 天、月、年（默认 天）。每次生成结果都按当前设置处理。Settings in the Decrement Calendar Date tool — "Amount" default 1; "Unit": Days, Months, Years (default Days). The result always uses the current settings.
「递减日历日期」免费吗？需要注册吗？Is the Decrement Calendar Date tool free? Do I need an account?
「递减日历日期」完全免费，无需注册或安装，打开网页即可使用，手机和电脑都能用；输入的内容只在你的浏览器本地处理。The Decrement Calendar Date tool is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.