Method
How the date calculator works
Days, weeks and hours use elapsed duration. Months use calendar-month arithmetic and clamp to the final valid day when the target month is shorter.
Counting clock time within a day rather than calendar days? The hours calculator measures the hours and minutes between two times, the time card calculator totals a week of shifts, the add time calculator adds or subtracts durations, and the military time converter switches between 24-hour and AM/PM times. The rest are in the time calculators collection.
Example
Date calculator example
Adding one month to 31 January reaches the last valid day of February rather than creating an impossible date.
FAQ
Date calculator FAQ
How do I subtract time?
Enter a negative amount.
Are days calendar days?
Yes. Use the business-days calculator when weekends must be excluded.
How are months handled?
The calendar month changes first, then the day is limited to the target month’s final date.