Date Calculator
Add or subtract days, weeks, months or years from any calendar date.
Enter a date and amount to calculate a new date.
Month and year calculations preserve the day when possible. If the target month is shorter, the result uses its last valid day, such as January 31 plus one month becoming February 28 or 29.
About the Date Calculator
The Date Calculator finds a new calendar date by adding or subtracting a whole number of days, weeks, months or years from a starting date.
Day and week calculations count exact calendar days. Month and year calculations preserve the original day when it exists in the target month, then use the final valid day when the target month is shorter.
For example, January 31 plus one month becomes February 28 in a common year or February 29 in a leap year. February 29 plus one year becomes February 28 when the next year is not a leap year.
The result includes a readable date, weekday, ISO date and the calculation used. Everything runs locally in the browser with no timezone conversion.
Key features
- Add or subtract calendar periods
- Days, weeks, months and years
- Correct month-end date clamping
- Leap-year aware results
How to use
- 1Choose the starting calendar date.
- 2Select Add or Subtract, enter a whole amount, and choose a unit.
- 3Review the resulting date, weekday and calculation explanation.
Frequently asked questions
- What happens when I add one month to January 31?
- The result uses the last valid day of February, which is February 28 in a common year or February 29 in a leap year.
- How does the calculator handle February 29 plus one year?
- If the target year is not a leap year, the result is February 28 because February 29 does not exist in that year.
- Can I subtract dates into an earlier year?
- Yes. Subtraction can cross months and years as long as the resulting date remains between year 0001 and year 9999.
- Can I enter a decimal amount?
- No. Calendar date offsets use non-negative whole amounts so every result has an unambiguous calendar meaning.
- Does daylight saving time affect the result?
- No. The calculation uses calendar dates without local times, so clock changes cannot move the result by a day.