Date Calculator
Add or subtract days, weeks, months and years from a date and find the resulting date and weekday.
Finds the date a number of years, months, weeks and days after or before a start date, with its weekday and ISO week — for deadlines, due dates and questions like “what date is 90 days from today”.
How the date is worked out
Years and months move first, as one shift in which a year is 12 months. The day of the month stays the same unless the target month is too short for it; then the date falls on that month's last day. One month after 31 January 2026 is 28 February 2026, and after 31 January 2024, 29 February 2024. The tool says so under the result whenever this happens.
Because the shift is a single step, the month end applies at most once: 1 year and 1 month after 29 February 2024 is 29 March 2025, where a year and then a month would stop at 28 March 2025. Excel's EDATE gives the same dates.
Weeks and days are then counted from that date, a week being 7 days. The start date itself is day 0, so 1 day after a Monday is the Tuesday.
Examples
90 days from 1 January 2026
90 days after 1 January 2026 is Wednesday, 1 April 2026.
6 months from 31 August 2026
February 2027 has no 31st, so 6 months after 31 August 2026 is its last day, 28 February 2027. Counting 6 months back from 28 February 2027 gives 28 August 2026, not 31 August: a month shift keeps the day of the month, not the distance from the month's end, so it cannot always be undone.
Counting back 12 weeks from 31 March 2027
To end a 12-week period on 31 March 2027, start it on 6 January 2027, a Wednesday, 84 days earlier.
Frequently asked questions
See also
- Working Days Calculator — to add working days instead, skipping weekends and holidays.
- Days Between Dates — to count the days between two dates you already have.