How to use the Date Calculator
- Choose Days between dates or Add / subtract.
- Enter the dates or the number to add or subtract.
- Press Calculate.
Date Calculator formula
Days between = End date − Start date (add 1 if both dates are counted).
Adding months keeps the same day number; if that day does not exist (e.g. 31 Feb), the last day of the month is used.
Worked example
1 January 2026 to 1 April 2026 = 90 days (31 + 28 + 31). 31 January 2026 + 1 month = 28 February 2026.
Frequently asked questions
How do I count days between two dates?
Enter both dates in the Days between dates mode. Tick 'Include end date' if both days should be counted.
How are weekdays counted?
All days from Monday to Friday between the dates are counted. Public holidays are not removed.
How do I find a date 90 days from today?
Use Add / subtract, keep today's date, enter 90 and choose Days.
What happens when adding a month to 31 January?
You get the last day of February, because 31 February does not exist.
Does it handle leap years?
Yes.