Date Calculator: Add or Subtract Days
Choose a starting date and an amount of time to add or subtract. The calculator returns the resulting date and its day of the week.
Result
- ISO format
- 2026-04-15
- Day of the week
- Wednesday
- Calendar days from start
- 90 days
- Start date
- Thursday, January 15, 2026
Formula
- New date = start date ± number of days
- Weeks are added as 7 days each
- Months and years move the calendar month, keeping the day of the month where it exists
How the Date Calculator works
Adding days or weeks is simple counting. Adding months is a calendar operation: one month after March 15 is April 15. When the target month is too short, the result is the last day of that month, so one month after January 31 is February 28, or February 29 in a leap year.
Business days skip Saturdays and Sundays. Deadlines set in business days, such as shipping estimates and contract notice periods, are counted this way.
Worked example
Adding 90 days to January 15, 2026 gives April 15, 2026, a Wednesday. Adding 3 months gives the same date here, but that is not always so: 90 days after July 1 is September 29, while 3 months after July 1 is October 1.
Frequently asked questions
What date is 90 days from today?
Leave the start date on today, enter 90 and choose days. The calculator shows the date and the weekday it falls on.
Is 3 months the same as 90 days?
Not usually. Three calendar months range from 89 to 92 days depending on which months are involved.
How does the calculator handle month ends?
If the starting day does not exist in the target month, it uses the last day of that month. January 31 plus one month is February 28 in a common year.
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Calculations run in your browser and nothing you enter is sent to a server. Results are provided for general information. Check critical figures independently before relying on them.