Date after N days
Find the date N days after a start date in UTC calendar days. Example: 2025-01-31 plus 30 days is 2025-03-02. Output is YYYY-MM-DD.
What to know
Enter a Start date and a whole number in the Days field, and the result is the calendar date that many days later, printed as YYYY-MM-DD. The formula is start + N x 86,400,000 ms on UTC midnight, so there is no daylight-saving drift.
The start day is day zero. Adding 0 returns the same date, adding 1 returns the next day, and 2025-01-31 plus 30 days is 2025-03-02 because February 2025 has only 28 days. Adding 30 days is not the same as adding one month, and the page never snaps to the end of a month.
Typical jobs are contract notice periods, return windows, trial expiries, invoice due dates and sprint planning. For an anniversary where the first day counts as day 1, add one less than the milestone, so the 100th day from 2025-01-01 is start plus 99, which is 2025-04-10.
The Days field takes whole numbers of 0 or more and flags decimals or negatives. To go backwards in time, open the subtract-days page, which uses the same arithmetic with the opposite sign.
A handy check is 7 days, which always lands on the same weekday one week later. Adding 14 or 28 gives fortnightly or four-week cycles without any month arithmetic.
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How to use Date after N days
- Enter Start date 2025-01-31.
- Type 30 in the Days field.
- Read the Result line, which shows 2025-03-02.
- Change Days to 365 to see 2026-01-31, one non-leap year later.
Quick answers
What is 90 days after 2025-12-01?
It is 2026-03-01. December has 30 days left after the 1st, then January adds 31, February 28 and 1 more day in March.
Does adding days skip weekends or holidays?
No. Every calendar day counts. For Monday-to-Friday counting, use the working-day mode of the date calculator.
Why does 2025-01-31 plus 30 days not land on 28 February?
Adding days is plain counting forward on the calendar, so it passes the end of February and arrives on 2 March. Month arithmetic behaves differently.
Can I add a fraction such as 1.5 days?
No. The field accepts whole numbers only, and shows an error for decimals.