When a target month is shorter, month and year calculations use its final valid day.
How to use this add or subtract days
- Choose a starting date.
- Select add or subtract and enter the amount.
- See the resulting date and weekday.
Add or subtract days, weeks, months or years
Use this date calculator when you know a starting date and a calendar amount. Add moves forward; subtract moves backward. One week is seven calendar days, while months and years follow the calendar rather than a fixed number of days. The result also shows the weekday, which helps check a deadline, delivery date or planned event.
What happens at the end of a month?
If the target month has no matching day, the result uses that month's last valid date. For example, adding one month to 31 January lands on 28 February in a non-leap year (or 29 February in a leap year). This avoids producing an impossible date and keeps the assumption visible.
Choose the right date tool
Use Days Between Dates when you need the gap between two known dates, or Business Days Calculator when Saturdays and Sundays should be excluded. For elapsed clock time, use the Time Duration Calculator.