About the date calculator
The Days Between Dates tab tells you how long it is from one date to another in days, in weeks and days, and in years, months and days. Tick "Include end day" when both the first and last day count, such as a hotel stay or a leave period.
The Add or Subtract tab moves a date forward or back by any mix of years, months and days and shows the weekday of the result. Years and months are applied first, then days.
How month ends work
When you add a month to January 31, there is no February 31, so the result is the last day of February. The calculator always clamps to the last valid day of the month in this way, and leap years are taken into account.
Formula
- Days between = end date − start date (+1 if the end day is included)
- Result = (date ± years and months, clamped to month end) ± days
Example
From January 15, 2024 to March 1, 2024 is 46 days, or 1 month and 15 days. Adding 1 month to January 31, 2024 gives February 29, 2024 because 2024 is a leap year.