Date Calculator
Math Calculators

Date Calculator

Find what date is a given number of days, weeks, months, or years from a start date, or count the number of days between two dates.

Resulting date
—

How It Works

In add/subtract mode, the calculator takes a start date and adds (or subtracts) a number of days, weeks, months, or years. For months and years it uses calendar arithmetic, so adding one month to January 31 lands on February 28 (or 29 in a leap year).

For days and weeks, the calculator adds the equivalent number of days directly, since every day has the same length. For months and years, it preserves the day-of-month when possible and clamps to the last day of the target month when the day does not exist there.

In days-between mode, the calculator counts the number of days on the calendar from the start date to the end date, inclusive of the end date. Leap years and months with different lengths are handled automatically.

Frequently Asked Questions

What happens when adding a month lands on a day that does not exist?
The calculator clamps to the last day of the target month. For example, adding one month to January 31 gives February 28 (or February 29 in a leap year), which is how most calendar libraries handle it.
Does this account for leap years?
Yes. The calculator uses the real calendar, so February has 29 days in leap years and 28 otherwise, and that is reflected in both the date arithmetic and the day counts.
Is the end date included in the days-between count?
Yes. The count is inclusive of the end date. For a pure difference, subtract one from the result or use the start date as the day before your desired start.

Related Calculators

Age Calculator Age in years, months, days from a birth date. Hours Calculator Weekly time card with daily and weekly hour totals. Unit Converter Length, weight, temperature, volume, speed, and data. acres to square feet Convert acres to square feet and back.