DateDelta

Add or Subtract Days Calculator

Skip the calendar counting — enter a start date and a day count, get the exact resulting date.

Start date

Days to add (negative to subtract)

Resulting date

2026-10-08

What you entered

Start date: 2026-09-08Days: +30

1
Add days to the start date
2026-09-08 + 30 days= 2026-10-08

Result

Resulting date: 2026-10-08

Adding 30 days to 2026-09-08 lands on 2026-10-08.

Adding and subtracting days from 1 January 2026

Each row shifts the same start date by the number of days shown. Negative values move backwards.

Days	Resulting date	Common use
-30	2 December 2025	A month earlier
-7	25 December 2025	A week earlier
+7	8 January 2026	One week later
+30	31 January 2026	Thirty-day term
+90	1 April 2026	Quarter
+180	30 June 2026	Half year
+365	1 January 2027	One year, non-leap

Adding 30 days is not the same as adding a month, as the +30 row shows by landing on 31 January rather than 1 February - month lengths vary, and contractual terms written in days behave differently from terms written in months. The +365 row lands exactly on 1 January 2027 because 2026 is not a leap year; the same arithmetic across a leap year would land a day short. Day-counting is the right approach for notice periods, incubation windows and payment terms, where a fixed number of days is what the agreement actually says.

Handles month and year rollovers automatically

Adding days across a month boundary (like 20 days from January 25th) or even a year boundary (December into January) requires correctly accounting for varying month lengths and leap years — this calculator handles all of that for you.

Common uses

Useful for calculating due dates, contract deadlines, return windows, or any 'X days from now' or 'X days before' question that's tedious to count by hand on a calendar.

Frequently asked questions

My 30-day return window started January 25 — what's the deadline?

January 25 + 30 days = February 24 (in a non-leap year). The calculator handles the month boundary automatically — no manual counting needed.

What date is 90 days from today?

Enter today's date and add 90 days — the calculator handles months of different lengths and even year boundaries. 90 calendar days is roughly 3 months but not exactly, since months have 28-31 days.

Can I subtract days too?

Yes — enter a negative number or use the subtract mode to count backward. Useful for questions like 'what date was 45 days ago?' or 'when should I have started a 60-day process to finish by this deadline?'