📅 计算平均日历日期Calculate Average Calendar Date
对多行日期取平均（按儒略日），输出最接近的日期。本地处理。Average several dates (by Julian day) and round to the nearest date. Processed locally.
使用说明与常见问题How-to & FAQ
「计算平均日历日期」是什么？What is the Calculate Average Calendar Date tool?
对多行日期取平均（按儒略日），输出最接近的日期。本地处理。Average several dates (by Julian day) and round to the nearest date. Processed locally.
如何使用「计算平均日历日期」？How do I use the Calculate Average Calendar Date tool?
每行输入一个 YYYY-MM-DD 日期，下方会显示这些日期的平均日期（四舍五入到天）。Enter one YYYY-MM-DD date per line; the average date, rounded to the nearest day, appears below.
平均日期怎么算？How is the average date worked out?
先把每个日期换成儒略日数（JDN），取算术平均，再四舍五入回日期。只输入一个日期时直接返回它本身并提示。格式不对的行会指出行号。Each date is converted to its Julian Day Number, the arithmetic mean is taken and rounded to the nearest day, and that day is turned back into a date. With a single date the date itself is returned, with a note. A line in the wrong format is reported with its line number.
用的是哪种历法？和时区有关吗？Which calendar is used, and do time zones matter?
所有日期都按外推格里高利历（proleptic Gregorian，即把现行公历规则向前一直沿用）计算，年份 0000–9999，0000 年即公元前 1 年。1582 年 10 月 5 日到 14 日在历史上采用格里高利历时被跳过，从未实际存在；页面仍按外推公历计算这些日期，并在结果下方给出提示。计算只用你输入的日期，不读取设备时钟，所以时区和夏令时不影响结果。输出的年份总是 4 位（如 0005-06-07）。All dates are proleptic Gregorian: today's calendar rules applied backwards without a break, for years 0000–9999 (year 0000 is 1 BC). The days 1582-10-05 to 1582-10-14 never existed in the Gregorian calendar as historically adopted — they were skipped — so the page still computes them as proleptic dates but shows a note below the result. Only the dates you type are used and the device clock is never read, so time zones and daylight saving time do not affect the result. Years are always printed with 4 digits, e.g. 0005-06-07.
输入和输出是什么样的？What does the input and output look like?
例如在「计算平均日历日期」中输入 2020-01-01 ⏎ 2020-01-03，输出为：2020-01-02（⏎ 表示换行）。The input 2020-01-01 ⏎ 2020-01-03 becomes 2020-01-02 (⏎ marks a line break).
「计算平均日历日期」免费吗？需要注册吗？Is the Calculate Average Calendar Date tool free? Do I need an account?
「计算平均日历日期」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 Calculate Average 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.