Add/Subtract Days Calculator
Add or subtract days from a date.
Inputs
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Formula
result date = start date + days (calendar arithmetic)
The start date is parsed at local midnight, then the native Date object adds whole days — so month and year rollovers (including leap-day handling) follow the JavaScript calendar rules automatically.
Worked example
30 days after 30 August 2026 is 28 September 2026 — crossing a 31-day month, with the weekday shown so you can spot that it lands on a Tuesday without opening a calendar app.
Where this can give the wrong answer
- Days must be a whole number; fractions like 0.5 aren't accepted.
- Adding a large negative number (up to −36,500) moves the date far into the past — useful for backdating, but verify the year if you're typing quickly.
- Leap day: adding 365 days from 1 March 2025 lands on 1 March 2026; adding from 28 Feb 2024 may pass through 29 Feb depending on direction.
FAQ
- No — it's exactly 30 day steps. 'One month later' depends on which month you start in (30 days from 31 Jan ≠ 30 days from 1 Feb in calendar terms).