Date Calculator

How the math works

The Add or subtractmode applies offsets in calendar units — years, months, weeks, and days — in that order. Adding one month to 31 January lands you on 28 February (or 29 in a leap year), not on 3 March; the browser's Date API clamps overflowing days to the last valid day of the target month. Weeks are treated as seven days, so adding 2 weeks is identical to adding 14 days.

The Duration betweenmode gives you three complementary views. "Duration" is the calendar breakdown (X years, Y months, Z days) — useful for describing the span in plain English. "Total days" is the raw count of days between the two dates. "Business days" counts every weekday (Monday through Friday) in the range and excludes weekends, which matches how most offices and courts count working days; holidays are not excluded, since holidays vary by country.

Negative durations are supported — if the end date is before the start date, you get negative values. All calculations run in your local timezone and never leave your browser. For moving between timezones, use the timezone converter. For ages in years, months, days, and live seconds, use the age calculator.