Can I subtract days instead of adding them?

Yes — switch the operation toggle to "Subtract" to move backward from your start date.

Does it handle month and year boundaries correctly?

Yes. The calculator uses full calendar-date arithmetic, so it correctly rolls over month lengths, year boundaries, and leap years.

What day of the week will the resulting date fall on?

The result includes the day of the week for the calculated date automatically.

Age, Date & Calendar

Date Calculator

Pick a starting date, choose whether to add or subtract, and enter a number of days to find the resulting date.

Your calculation is performed in your browser.

Enter a start date and number of days to calculate the result.

How it works

The calculator takes your starting date and moves forward or backward by the exact number of days you enter, correctly rolling over month and year boundaries and accounting for leap years.

Formula & methodology

Days are added or subtracted using whole-day calendar arithmetic, so month lengths and leap years are handled automatically. Months are never approximated as 30 days.

AddResult date = Start date + N days

SubtractResult date = Start date − N days

What each term means

Start date: The date you begin from.
Number of days (N): A whole number of days (0 or more).

Worked example

Starting from January 20, 2027 and adding 45 days gives March 6, 2027, a Saturday.

Common uses

—Finding a deadline or due date by adding a fixed number of days to a start date.
—Working out a delivery, lease, or warranty end date from a start date and a term length.
—Planning backward from an event date to find when preparation needs to begin.

Important notes

—The number of days must be a whole number of 0 or more; choose "Subtract" to go backward in time.