Date Calculator
Add or subtract days, weeks, months and years from a date, and see the resulting date and its weekday.
Choose a start date, whether to add or subtract, and how much. Leave a part blank for zero. The result appears as soon as the entries are valid.
How to Use the Date Calculator
- Choose the start date.
- Choose Add or Subtract, then enter the years, months, weeks and days. Any part can be left blank.
- Read the resulting date and its weekday. Change any entry to see it update. Reset clears everything.
How the Date Is Calculated
The calculator works in the same order every time. Years and months come first, together, as whole calendar months (one year is twelve months). Weeks and days come after that, as plain calendar days (one week is seven days).
The dates are calendar dates, so a time zone or a daylight saving change cannot move the answer. Supported dates run from the year 1 to the year 9999, and an entry that would land outside them is not calculated.
Month Ends and Leap Years
Months have different lengths, so "one month" is not a fixed number of days. When the day of the month does not exist in the target month, the last day of that month is used: one month after 31 January is the last day of February. When this happens the result says so.
Because of that, the calculation is not always reversible. Adding a month to 31 January gives the last day of February, and subtracting a month from that gives 28 January, not 31 January. From 29 February, one year later is 28 February in a year that is not a leap year. Leap years follow the Gregorian rule: divisible by 4, except a century year unless it is divisible by 400 (2000 and 2024 are leap years, 1900 and 2100 are not).
Example
Adding 2 weeks and 3 days to 10 March 2026 gives 27 March 2026, a Friday. Adding 1 month to 31 January 2026 gives 28 February 2026, because February is shorter than January, and subtracting 1 month from 31 March 2026 gives 28 February 2026 for the same reason.
Common Uses
- A deadline, due date or end date that is a set time after a start.
- The end of a notice period, a trial or a warranty.
- A date a number of weeks or months before an event.
- The date a number of days from a booking or a delivery.
This calculator counts every calendar day. It does not skip weekends, calculate business days or public holidays, or use the time of day. See the disclaimer.
To find how far apart two dates are instead, use the Date Difference Calculator.
Date Calculator FAQ
What order are the years, months, weeks and days applied in?
Years and months first, then weeks and days. This keeps the result the same whichever way you enter an amount.
What happens when I add a month to the 31st?
If the next month has no 31st, the last day of that month is used, and the result tells you the date was adjusted.
Why does subtracting not always undo adding?
After a month-end adjustment the original day is lost. 31 January plus one month is 28 February, and 28 February minus one month is 28 January.
Does it skip weekends or holidays?
No. It counts every calendar day. Weekends, business days and holidays are not part of this calculator.
Does the time zone change the result?
No. The dates have no time of day, so the result is the same anywhere.