DateAndTimeCalculator.org

Add or Subtract Days from a Date

Add or subtract days, weeks, months or years from any date and see the resulting date and weekday. Handles month ends and leap years correctly.

Last reviewed: 30 July 2026

Period to apply

Years and months are applied first, then weeks and days. This matters at the end of a month — see the explanation below.

How this calculation works

Years and months are applied first, followed by weeks and days. The order is deliberate and it changes the answer, so it is worth understanding.

Month-end clamping

Adding a month means moving to the same day number in the next month. When that day does not exist, the result is clamped to the last day of the target month: 31 January plus one month is 28 February, and 31 March plus one month is 30 April. Any days you add are then counted from that clamped date.

A consequence worth remembering is that this arithmetic is not reversible. 31 January plus one month is 28 February, but 28 February minus one month is 28 January, not the 31st. If a contract or deadline depends on this, check how the wording defines a month.

Leap years

February is given 29 days in a leap year, so adding one month to 31 January 2028 gives 29 February 2028. Adding a year to a 29 February date clamps it to 28 February in the three following years.

Weeks and days

Weeks are simply seven days each, and days are added as whole calendar days. Neither is affected by month lengths, leap years or daylight saving.

Worked example

31 January 2026, add 1 month and 3 days

  • Add one month to 31 January: there is no 31 February, so this clamps to 28 February.
  • Add three days to 28 February: 3 March 2026.

Applying the three days first would give 3 February, and then one month would give 3 March as well — but this is a coincidence of this particular example, not a general rule.

Limitations

  • Weekends and public holidays are not skipped.
  • Times of day are not handled; the result is a calendar date.
  • Very large values are accepted but only sensible within the range of ordinary calendar dates.

Frequently asked questions

What happens when I add a month to 31 January?

You get 28 February, or 29 February in a leap year. There is no 31 February, so the result is clamped to the last day of the target month. This is the same rule used by ISO 8601 and by most programming languages and spreadsheets.

Does adding a month and then another month give the same result as adding two months?

Not always, and this surprises people. 31 January plus one month is 28 February; adding another month to that gives 28 March. Adding two months to 31 January in one step gives 31 March. Always add the full period in one calculation rather than in stages.

How do I subtract instead of add?

Choose "Subtract" from the direction menu, or enter a negative number. Both work the same way and the result explains which direction was applied.

Are weekends and public holidays skipped?

No. This calculator moves by calendar days, so it will happily land on a Sunday or Christmas Day. If you need the result to land on a working day, use the add working days calculator instead.

What about 29 February when adding years?

Adding one year to 29 February 2028 gives 28 February 2029, because 2029 has no 29th. Adding four years gives 29 February 2032, since that is a leap year again.