Date Add / Subtract Calculator
How it works
Days and weeks are added as a straightforward day count. Months and years add to the month or year component directly, then clamp the day of month down to the target month's actual last day if it would otherwise overflow — so Jan 31 + 1 month lands on Feb 28 (Feb 29 in a leap year), never March 3. A negative amount subtracts using the same rules in reverse.
Everything runs in UTC end to end, so the date you get back does not depend on your browser's own timezone or the exact moment you happen to load the page.
Frequently asked questions
Why does this run in UTC instead of my local timezone?
So the answer never silently shifts by a day depending on where you are or exactly when your clock crosses midnight. A page running purely in the browser has no bundled timezone database, and calendar arithmetic done in local time can land on a different calendar day right around a DST change or your own local midnight — UTC has no such boundary to cross. This is the same reasoning the Date Format Converter and Timestamp Converter on this site already use.
What happens when adding months or years overflows the month?
The day of month is clamped down to the target month's actual last day rather than spilling over into the next month. Jan 31 + 1 month gives Feb 28 (Feb 29 in a leap year) — not March 3, which is what you would get if the extra 2 or 3 days simply carried forward.
Can I subtract instead of add?
Yes — enter a negative amount. -10 days, -1 months and -1 years all subtract from the date exactly as you would expect, using the same rules (including the month-end clamping) in reverse.