Two modes in one page. Difference mode measures the span between two dates: years/months/days, total days, weeks, and business days (Monday–Friday, holidays not included). Add mode does calendar arithmetic — add or subtract days, weeks, months or years from a date.
Month and year arithmetic is calendar-aware: January 31 + 1 month lands on February 28 (the day is clamped to the target month and the page tells you), and leap years are handled exactly.
Frequently asked questions
Does the day count include the end date?
By default no — a span counts whole days between the dates. Tick the checkbox to include the end date itself, which is how visa and notice periods are usually counted.
Why does Jan 31 + 1 month give Feb 28?
February has no 31st day, so the day is clamped to the month's last day — the standard convention.
Do business days include public holidays?
No — only weekends are excluded; local public holidays vary by country, so add them yourself.
中文说明
一页两种模式。间隔模式计算两个日期之间的差：年/月/日、总天数、周数与工作日（周一至周五，不含法定节假日）；加减模式做日历运算——从某日期加减日、周、月、年。
月与年的加减遵循日历规则：1 月 31 日 + 1 个月落在 2 月 28 日（日被钳制到目标月末，页面会提示），闰年精确处理。
常见问题
天数包含结束日当天吗？
默认不包含——间隔统计的是两日期之间的整天数。勾选后包含结束日当天，这也是签证期限、通知期通常的算法。
为什么 1 月 31 日 + 1 个月是 2 月 28 日？
2 月没有 31 日，日被钳制到当月最后一天——这是通用约定。
工作日包含法定节假日吗？
不包含——只剔除周末；各国法定节假日不同，请自行留意。