Add or Subtract Days From a Date

How does this calculator work?

Select a starting date, choose add or subtract, then enter the calendar years, months, weeks and days. Years and months are applied before weeks and days. If a target month has fewer days than the starting date, its last valid day is used.

Quick example

Adding one month to January 31, 2026 gives February 28, 2026, not March 3.

Calendar math is not always simple day math

Adding seven days means moving forward exactly seven calendar dates. Adding one month means advancing the calendar month, which can produce a different result than adding 30 days.

Worked example: adding two weeks

Starting on 1 March, adding two weeks moves the date forward 14 days to 15 March.

Month ends and leap years

For calculations involving January 31, February 29 or other month-end dates, review the displayed result because months have different lengths and calendar arithmetic needs a defined month-end convention.

Frequently asked questions

Does one month mean 30 days?

No. It means one calendar month, preserving the day when possible and otherwise choosing the last day of the month.

Can I subtract time?

Yes. Choose Subtract and enter the same calendar intervals.

Is adding 1 month the same as adding 30 days?

No. A calendar month can contain 28, 29, 30 or 31 days.

Can I calculate a deadline using only weekdays?

This tool moves through calendar dates. Use the Business Days Calculator to count weekdays between two dates.