Free Online Date Calculator
Find the duration between two dates, add or subtract time, and count business days.
Calculations use calendar dates and account for leap years and varying month lengths.
What is Date Calculator?
A date calculator helps you work with calendar dates without counting by hand. It can measure the duration between two dates in years, months, and days, add or subtract a span of time from a date, and count the business days between two dates. It accounts for leap years and varying month lengths automatically.
How to use it
- Pick a mode: Duration, Add / Subtract, or Business Days.
- For Duration, enter a start and end date to see the time between them.
- For Add / Subtract, choose a base date, an amount, and a unit (days, weeks, months, or years).
- For Business Days, enter two dates to count weekdays between them.
How date math works
Duration counts full years, then full months, then remaining days between two calendar dates. Adding months or years uses calendar math with end-of-month clamping (for example, January 31 + 1 month becomes the last day of February). Business days count Monday through Friday, inclusive of both the start and end dates.
Frequently asked questions
The calculator counts complete years first, then complete months, then the remaining days. It also shows the total number of days, weeks, and months for reference.
Yes. Leap years and February 29 are handled correctly in both duration and add/subtract calculations. Adding one year to February 29 in a leap year lands on February 28 of the following non-leap year.
If the target month does not have enough days, the date is clamped to the last day of that month. For example, January 31 plus one month gives February 28 (or 29 in a leap year).
Business days are Monday through Friday, inclusive of both the start and end dates you enter. Weekends are excluded. Public holidays are not accounted for, since they vary by region.
The calculator swaps the dates automatically and flags that they were reversed, so you still get a valid result.
Yes. Select Weeks as the unit and enter any amount. Subtracting weeks moves the date backward by that many seven-day periods.
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