Date Calculator – Add or Subtract Days
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How to use it
- Pick a start date (today by default).
- Choose add or subtract, then enter years, months, weeks and/or days.
- Read the resulting date and weekday. For working days only, use the business days calculator.
Examples
90 days from a date
90 days after October 1, 2026 is Wednesday, December 30, 2026.
Month ends
January 31 plus one month is February 28 (or 29 in a leap year) — the calculator keeps you in the right month instead of spilling into March.
How dates are added
Years and months are added first, on the calendar: the day of the month stays the same unless that month is shorter, in which case it moves to the month's last day. Weeks and days are then added as exact numbers of days.
That order matches how people describe deadlines like “one month and 10 days from today”. Subtraction works the same way in reverse.
Frequently asked questions
Is “30 days” the same as “one month”?
No. One month from January 15 is February 15 (31 days later), while 30 days from January 15 is February 14. Contracts usually specify which one they mean.
Does it count the start date?
No. Adding 1 day to Monday gives Tuesday. If your rule counts the start date as day 1, subtract one day from the number you enter.
Can I count only working days?
Use the business days calculator, which skips weekends and any holidays you list.
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More in Date & Time · Last reviewed October 2026