What can the Date Calculator do?
The Date Calculator handles the two date questions people ask most often:
- How long is it between two dates? Choose “Between two dates”, enter a start and end date, and get the total number of days, the weeks and days, the exact years-months-days difference, total months and the number of weekdays.
- What date is it X days, weeks, months or years from a date? Choose “Add or subtract”, pick the unit and whether to add or subtract, and get the resulting date with its day of the week, day of the year and ISO week number.
Every calculation counts real calendar days, including leap years, so you can rely on it for contracts, deadlines, travel plans, project schedules, ages and anniversaries. Looking for something more specific? Try the Days Between Dates counter, the Add Days to Date calculator (with business days) or the Days Until Date countdown.
How the difference between two dates is calculated
The calculator converts both dates to a day number and subtracts them. By default the start date is not counted and the end date is — the same way you would say that from Monday to Wednesday is two days. Tick Include the end date when you need to count both days, for example the number of days in a hotel stay including check-out day, or the length of an event that runs “from the 1st to the 10th inclusive” (10 days rather than 9).
Days between = end date − start date (+ 1 if the end date is included)
The years-months-days figure is calendar-aware. From January 31 to March 1 is 1 month and 1 day: January 31 plus one month lands on the last day of February, and one more day reaches March 1. Total weeks are simply days ÷ 7, and total years divide by the average Gregorian year of 365.2425 days.
Adding and subtracting days, weeks, months and years
Adding days or weeks is exact arithmetic — a week is always 7 days. Months and years are calendar units of different lengths, so the calculator moves to the same day number in the target month. When that day does not exist, it uses the last day of the month instead and tells you so:
| Start date | Operation | Result |
|---|---|---|
| January 31, 2027 | + 1 month | February 28, 2027 |
| January 31, 2028 | + 1 month | February 29, 2028 (leap year) |
| February 29, 2028 | + 1 year | February 28, 2029 |
| March 31, 2027 | − 1 month | February 28, 2027 |
| October 5, 2026 | + 90 days | January 3, 2027 |
Negative numbers are accepted too: adding −10 days is the same as subtracting 10. Numbers must be whole — enter 1 week and 3 days as 10 days.
Leap years
A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 2024 and 2028 are leap years, 2100 is not, and 2000 was. The calculator applies these rules automatically to every calculation, so February 29 is counted whenever it exists.
Weekdays and business days
The difference result shows how many of the days are weekdays (Monday to Friday) and how many fall on weekends. If you need to add a number of working days rather than calendar days, use the Add Days to Date calculator with the business-days option, which can also skip US federal holidays. For legal filing deadlines, the Court Date Calculator applies weekend and holiday roll-over rules.
More date tools
- Date to Date Calculator — duration between two dates in every unit, down to seconds.
- Days From Date — what date is N days from a given day.
- Subtract Days From Date — count back to a past date.
- Add Weeks to Date and Add Months to Date.
- Time and Date Calculator — include hours and minutes.
- Due Date Calculator — estimate a pregnancy due date.