Date Calculator
Add or subtract days, weeks, months, or years from a date.
Try an example
Saturday, January 31, 2026
About this calculator
How This Date Calculator Works
Enter a start date, a number of days, weeks, months, or years, and choose whether to add or subtract — the calculator returns the resulting date, including the day of the week.
Worked Example
Adding 90 days to January 1, 2026 lands on April 1, 2026, a Wednesday.
Why Month and Year Math Isn't Just "30 Days"
Adding months or years shifts the calendar month/year directly rather than converting to a fixed number of days — adding 1 month to January 31 doesn't reliably land on a real date (since not every month has 31 days), so the underlying date logic handles month-length differences and leap years automatically rather than approximating a month as exactly 30 days.
Common Uses
- Deadlines and due dates — count forward a fixed number of days from a contract signing or invoice date
- Return and warranty windows — most retailers use a fixed day count (30, 60, 90 days) rather than calendar months
- Anniversaries and milestones — count years forward from a start date
- Pregnancy and project planning — count backward from a known target date to find a starting point
Worked example
Adding 30 days to January 1, 2026 lands on January 31, 2026.
Frequently asked questions
Does adding months keep the same day of the month?
Usually — adding 1 month to January 31 would land on a date that doesn't exist in February, so the calendar automatically rolls it forward to the nearest valid date (e.g., March 2 or 3, depending on the month lengths involved).
Does this account for leap years?
Yes — all date arithmetic uses actual calendar dates, so February's length and leap years are handled automatically rather than assuming a fixed number of days per month or year.
Can I calculate a date in the past?
Yes — choose "Subtract" to count backward from the start date instead of forward.