Everything About Date Calculation
How many days until a contract expires? How many weeks does a project span? What date is 100 days from today? Date arithmetic comes up everywhere, but uneven month lengths make it hard to do in your head. This calculator handles general-purpose date math in two modes: days between dates, and date add/subtract.
The difference mode shows the total day count alongside a weeks breakdown (weeks + days) and a calendar breakdown (years, months, days). Days are counted excluding the start date and including the end date, with an inclusive "both ends counted" value shown for anniversary-style counting. Turning on the weekend option gives business days with Saturdays and Sundays removed — public holidays are not included, so subtract those manually.
The add/subtract mode returns the date and weekday N days, weeks, months, or years before or after any base date. Presets for D+50, +100 days, and +1000 days make milestone planning quick, and month arithmetic clamps overflow dates to the end of the month (Jan 31 + 1 month → Feb 28). It is handy for billing cycles, expiry dates, and legal deadlines too.
This tool focuses on general date arithmetic rather than countdowns. For live D-day tracking and managing multiple anniversaries, use the D-day Calculator; for Korean and international age calculation, use the Age Calculator. Everything is computed instantly in your browser using your device's local time zone.