Date Add Calculator

Add days, weeks, months, or years to any date and get the resulting date — handles month-end clamping correctly.

Inputs

Whole number — use a negative number to subtract.

Result

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How to use this calculator

  • Pick the base date.
  • Enter how many days, weeks, months, or years to add. Use a negative number to go backwards.
  • Read the resulting date plus the day of the week it lands on.

About this calculator

Adding to a date sounds simple but has gotchas — Jan 31 + 1 month is February 28 or 29, not "Feb 31". This calculator follows the standard "clamp the day-of-month" rule used by date libraries, and shows the resulting day of the week along with the absolute day count for sanity-checking.

Frequently asked

What happens when I add a month to Jan 31?+
You get Feb 28 (or Feb 29 in a leap year). The calculator clamps the day-of-month to the last valid day of the target month. Adding another month gets you Mar 28 (or 29) — note that month-add is not the inverse of itself when day clamping kicks in.
Can I subtract by entering a negative amount?+
Yes. -30 days is the same as the date-subtract calculator with +30 days.
Why is "weeks" just days × 7?+
Weeks have no day-of-month edge case to worry about, so they are pure 7-day multiples. Weeks are still useful as a unit because users often think in them (e.g. "due in 6 weeks").
How are leap years handled when adding years?+
Adding 1 year to Feb 29 in a leap year clamps to Feb 28 in the next year (which is not a leap year). Adding 4 years lands on Feb 29 again.
Does the calculator account for time zones?+
No — inputs are date-only and operate in UTC. Adding 30 days will not surprise you with a 23-hour or 25-hour day shift.

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