Date Calculator
Add or subtract days, weeks, months or years from any date.
Resulting date
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What date is 90 days from today? What was the date 6 weeks ago? Enter a starting date, choose add or subtract, and set any mix of years, months, weeks and days.
The result shows the date and the day of the week, which is handy for deadlines, due dates, return windows and warranty periods.
How date calculator works
Years and months are applied first, then weeks and days. If the starting day does not exist in the target month, for example 31 January plus one month, the result is the last day of that month.
Days and weeks are exact calendar days, so leap years and month lengths are handled for you.
The formula
New date = start date ± (years, months) ± (weeks × 7 + days)Month arithmetic clamps to the end of the month: 31 Jan + 1 month = 28 or 29 Feb.
Worked example: 90 days after 15 January 2026
January has 16 days left after the 15th, February 2026 has 28, March has 31.
16 + 28 + 31 = 75, and 15 more days brings you into April.
Result: Wednesday, 15 April 2026.
When to use this tool
- Finding the last day of a 30-day return or cancellation window.
- Setting a project milestone a set number of weeks after kickoff.
- Working back from an event date to see when to start.
- Checking which weekday a future date will fall on.
Common mistakes to avoid
- Adding months by counting 30 days each. Use the month field so real month lengths apply.
- Forgetting that a deadline of “within 30 days” may or may not include the start date. Check the wording.
- Assuming the result is a working day. Weekends and holidays are not skipped.
Frequently asked questions
- How do I add days to a date?
- Enter the start date, choose Add, type the number of days and read the result. Weeks, months and years work the same way.
- What date is 90 days from today?
- Set the start date to today, choose Add and enter 90 days. The result and its weekday appear immediately.
- What happens when adding a month to the 31st?
- The result moves to the last day of the target month, so 31 January plus one month is 28 or 29 February.
- Does it skip weekends?
- No. It uses calendar days. For working days between two dates, use the date difference calculator.
Learn more
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Results are for information only and are not financial, legal or medical advice. The calculation logic is covered by automated tests, and examples on this page are worked out and re-checked before publishing. Spotted a mistake? Tell us.