Date Calculator

Count the exact number of days between two dates, or add and subtract days from a date.

How date differences are calculated

Each date is converted to a day count, and the difference between the two counts is the exact number of days between them. This automatically handles months of different lengths and leap years — February has 29 days in a leap year, which is any year divisible by 4, except century years not divisible by 400. Adding or subtracting days works the same way: move the day count forward or backward, then convert it back to a calendar date.

Worked example

From 15 January 2026 to 1 March 2026 is 45 days (16 remaining days in January after the 15th, 28 days in February 2026, plus 1 March). Adding those same 45 days to 15 January 2026 also lands on 1 March 2026 — try both calculators above to check.

How to use this calculator

1. For a difference, pick a start date and an end date and select Calculate difference.
2. For a deadline or countdown, pick a starting date, enter the number of days, and choose add or subtract.
3. The results show the new date with its day of the week, or the gap in days, weeks and approximate years.

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