Total days between two dates
The simplest date difference counts elapsed calendar days between a start date and an end date.
Calendar years, months and days
When a difference is expressed in years, months and days, the calculation must account for the actual sequence of calendar months rather than treating each month as a fixed number of days.
Why month lengths matter
- Some months contain 31 days.
- Some months contain 30 days.
- February normally has 28 days.
- February has 29 days in a leap year.
Inclusive vs exclusive date counting
Some situations count only elapsed days between dates, while others include both the starting and ending date. Always confirm which convention the task requires.
Adding or subtracting days
Date arithmetic can also be used to find a future or past date by adding or subtracting a specified number of days from a starting date.
Common date calculations
- Days until an event
- Days since an event
- Project durations
- Deadlines
- Age calculations
- Adding or subtracting a time period
For ordinary calendar-date calculations, dates are usually treated independently of time zones. Precise timestamp differences may require time-zone and daylight-saving handling.