Date Calculator: Add or Subtract Days
Add or subtract days, weeks, months and years from any date
Add to find a deadline; subtract to find a start date.
Resulting date
23 October 2026
Friday · 21 days from 2 October 2026
Weekday
Friday
Days apart
21
Weeks apart
3.0
Working
Years and months are applied first and clamp to the end of the target month, then weeks and days are added. The starting date itself is not counted, so 1 August plus 21 days is 22 August.
About this tool
Useful when a notification says something like 'within 21 days of publication' or 'the fee window closes 15 days after the application start date'. Enter the starting date, add or subtract the offset, and the calculator returns the exact date along with its weekday.
Month arithmetic clamps to the end of the month, which is the convention recruiters use: one month after 31 January is 28 February, not 3 March.
Frequently asked questions
›How are months added?
By calendar month, with the day clamped to the last valid date of the target month. Adding one month to 31 March gives 30 April.
›Does it count the start date?
No. Adding 21 days to 1 August gives 22 August. If a notification counts inclusively, subtract one day.
›What is the difference between this and the Days Calculator?
This one moves a date forward or backward by an offset. The Days Calculator measures the gap between two dates you already have.