Add or Subtract Days Calculator

Choose a start date, press Add or Subtract, then enter an amount and a unit. The result shows the full date with its weekday, which tells you straight away whether a deadline lands on a weekend.

Days and weeks are exact: a week is always 7 days. Starting from Monday 19 October 2026:

Note that 30 days and one month are not the same thing. Thirty days from 19 October is 18 November; one month from 19 October is 19 November.

Months and years keep the same day number and move the month or year. That works until the day doesn't exist in the target month. When it doesn't, the extra days spill into the next month instead of stopping at the month's last day:

"31 February" becomes 3 March in 2026 and 2 March in leap-year 2028, and so on. Subtracting is affected too: one month before 31 March lands on 3 March, not 28 February.

If you need the last day of a month, work from the 1st instead. To get the end of February from 31 January, add one month to 1 February (1 March 2026), then subtract one day: Saturday, 28 February 2026.

The start date is day zero. Adding one day to a Monday gives Tuesday. That matches the usual reading of "within 14 days of 19 October", which ends on 2 November.

Some rules count the start date as day one, and then the deadline is a day earlier than the tool shows. If a notice, a return window or a filing period has legal weight, check the wording of the rule rather than relying on either convention.

The tool also counts every calendar day. It doesn't skip weekends or public holidays, so a "10 working days" deadline needs a different approach: count forward on a calendar, or try end dates in the Business Days Calculator on this site until it shows the number you need.