Date Calculator
Start from any date, add or take away years, months, weeks and days, and see the exact date you land on, with the weekday.
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The formula
New date = start date +/- (years, months, weeks, days). Months are applied first, then days.
What it does
Pick "Add to a date" or "Subtract from a date", enter a start date and the amounts. You can mix units, for example 1 year, 2 months and 10 days.
Choose "Days between two dates" if you want the gap between two dates instead.
How months and month ends are handled
Months and years are applied first, then weeks and days. If the start day does not exist in the target month, we use the last day of that month. So 31 January plus 1 month is 28 February, not 3 March.
Worked examples
| Start | Change | Result |
|---|---|---|
| 3 Oct 2026 | + 90 days | 1 Jan 2027 |
| 31 Jan 2026 | + 1 month | 28 Feb 2026 |
| 1 Mar 2026 | - 1 day | 28 Feb 2026 |
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Add to a date; Start date: 2026-10-03; Months: 1 | Result: Tuesday, November 3, 2026 |
| Add to a date; Start date: 2026-01-31; Months: 1 | Result: Saturday, February 28, 2026 |
| Subtract from a date; Start date: 2026-10-03; Years: 1; Months: 2; Days: 10 | Result: Thursday, July 24, 2025 |
| Add to a date; Start date: 2026-02-28; Years: 2 | Result: Monday, February 28, 2028 |
Date Calculator: frequently asked questions
Does the calculator count the start date?
No. Adding 1 day to 1 March gives 2 March. The start date itself is day zero.
What happens when I add a month to the 31st?
We move to the last day of the shorter month. Adding one month to 31 January gives 28 February (29 in a leap year), which matches how most calendars and spreadsheets behave.
Does it take leap years into account?
Yes. Calculations use real calendar dates, including leap days and the different lengths of months.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026