Date Add-Subtract Calculator

Add or subtract years, months, weeks and days from a date to find a new date.

Start date
July 4, 2026

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How it works

Pick a starting date and enter how many years, months, weeks, and days to add or subtract. The tool shifts the date using the date-fns library, which handles month-length and leap-year edge cases correctly — adding one month to January 31 lands on the last valid day of February. A business-days mode counts only weekdays, skipping Saturdays and Sundays, which is useful for deadlines. The result shows the new date, its weekday, and how many days it is from today. All math is local.


              today + 90 days → resulting date

Common use cases

  • Finding the date 90 days from today for a return or warranty window.
  • Counting a deadline that falls a number of business days out.
  • Working out a due date by adding weeks to a start date.

Frequently asked questions

How are months handled when the day does not exist?

date-fns clamps to the last valid day of the target month. Adding one month to January 31 gives February 28 (or 29 in a leap year) rather than rolling into March.

What does business-days mode do?

It counts only Monday through Friday, skipping weekends, so adding 5 business days to a Wednesday lands on the following Wednesday. Public holidays are not subtracted, since those vary by country.

Can I subtract as well as add?

Yes. Switch to subtract mode, or enter the operation direction, to move backward in time and find a past date from your start date.