Add or Subtract a Date Calculator
Add or subtract a date using calendar years, months, weeks, and days. See the exact target weekday, total calendar-day movement, and any month-end adjustment.
Written and checked by TheToolNet Editorial Team · Last reviewed: October 10, 2026 · Editorial method
Years and months follow the calendar. Weeks equal seven days, and days are exact 24-hour calendar steps in UTC.
Add or subtract from a date
How date addition works
The calculator applies years and months first, preserving the day number when possible. If the target month has fewer days, it clamps to that month's final day. It then applies weeks and days. This makes month arithmetic explicit instead of pretending every month has a fixed length.
Worked examples
| Starting date | Change | Result rule |
|---|---|---|
| January 31, 2026 | Add 1 month | February 28, 2026, because February is shorter |
| March 1, 2026 | Subtract 15 days | February 14, 2026 |
| October 10, 2026 | Add 12 weeks | Add exactly 84 calendar days |
Calendar days versus business days
This page includes weekends and holidays. To skip weekends and optionally observed U.S. federal holidays, use the business-day calculator.
Frequently asked questions
Can I find a date in the past?
Yes. Choose “Subtract time,” then enter the units to move backward.
Does one month always mean 30 days?
No. A calendar month moves to the corresponding date in the next or previous month. Month lengths vary from 28 to 31 days.