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Date calculator
Add or subtract days, months, and years from a start date. The result shows the full date and its weekday.
Result date
InvalidPick a valid start date.
A free date calculator that adds or subtracts any combination of years, months, and days from a start date and instantly shows you the resulting date along with its weekday. Useful for deadline planning, scheduling, age calculations, and any situation where you need to count forward or backward from a known date.
How to use the date calculator
- Enter or pick the start date using the date input.
- Choose the operation — Add or Subtract.
- Enter the number of years, months, and/or days to offset.
- The result date and its weekday appear instantly.
How date arithmetic works
The calculator adds or subtracts years and months first (adjusting for month-end edge cases such as adding one month to January 31), then adds the remaining days. This matches the way people naturally reason about dates — one month from January 31 is February 28, not March 2 or 3.
Common date calculation scenarios
- Finding a deadline 90 days from today or a contract start date.
- Working out an expiry date a fixed number of months in the future.
- Calculating what date falls 18 years after a birthdate.
- Checking what day of the week a future date falls on.
Frequently asked questions
Can I add months and days at the same time?
Yes. Enter values in any combination of the years, months, and days fields — the calculator applies them together in a single step.
How does the calculator handle month-end dates?
It clamps to the last day of the result month. Adding one month to January 31 gives February 28 (or 29 in a leap year), not an overflow into March.
Does the date calculator account for leap years?
Yes. It uses standard calendar rules, so February 29 is handled correctly when adding or subtracting across leap years.
Can I subtract dates to find a duration?
For finding the difference between two dates, use the Time Between Dates tool on this site.