About the Date Difference Calculator
This date difference calculator measures the time between two dates in every unit people ask for: years, months and days; total days; weeks and days; total months; weekdays and weekend days; and hours, minutes and seconds. Enter a start date and an end date and the breakdown appears instantly.
Use it to work out how many days are between two dates for a contract or lease, the length of a project or employment, days until or since an event, a notice or cooling-off period, or the duration of a trip. Choose whether to include the end date — include it when both the first and last day count (a hotel stay counted in days, a 1–31 March campaign), and leave it off to count nights or elapsed time.
Month and year differences are counted in whole calendar months, so they respect real month lengths and leap years rather than assuming 30-day months. If the end date is before the start date, the result is shown as a negative gap.
How to use the date difference calculator
- 1Enter the start date.
- 2Enter the end date (it can be before the start for a negative gap).
- 3Turn on “Include the end date” if both days should count.
- 4Read the years-months-days result and the total days.
- 5Check the table and chart for weeks, weekdays and hours.
Formula and method
Total days is the exact count of calendar days from the start date to the end date, with leap days included. Weeks are days ÷ 7, and decimal years use the average Gregorian year of 365.2425 days.
The years-months-days breakdown counts whole calendar months from the start date and then the leftover days, clamping to the last day of a month when the start day does not exist in it — so 31 January to 1 March is 1 month (to 28 February) and 1 day in a common year. Weekdays count Monday–Friday dates from the earlier date up to (but not including) the later date, or through the later date when the end date is included.
- Days
- Calendar days between the two dates
- 365.2425
- Average length of a Gregorian year in days
Worked examples
1 January to 29 September 2026
From 1 January to 29 September 2026 is 271 days: 8 whole months (to 1 September) plus 28 days. That is 38 weeks and 5 days, of which 193 are weekdays and 78 are weekend days.
Length of a lease: 15 March 2025 to 14 March 2027, end date included
Counting both the first and last day, the lease runs 730 days — exactly 2 years, since neither year contains 29 February within the range.
End date before start date
20 October is 66 days before 25 December, so the result is negative: 2 whole months (20 Oct to 20 Dec) plus 5 days back. The range contains 48 weekdays.
Frequently asked questions
How do I calculate the number of days between two dates?+
Subtract the start date from the end date. This calculator does it exactly, including leap years. Add one day if you want to count both the first and last day, for example when counting days of an event.
Should I include the end date?+
Leave it off to measure elapsed time or nights (a hotel stay from 1 to 5 March is 4 nights). Include it to count calendar days where both ends count (1 to 5 March inclusive is 5 days).
How many weeks are between two dates?+
Divide the total days by 7. The calculator shows both whole weeks plus days and the decimal number of weeks — for example 271 days is 38 weeks and 5 days, or 38.71 weeks.
How are months counted when months have different lengths?+
Months are counted as whole calendar months from the start date, so 15 January to 15 February is 1 month even though it is 31 days. Leftover days are added after the last whole month.
How many days are in a year?+
A common year has 365 days and a leap year 366. Leap years are divisible by 4, except century years that are not divisible by 400 — so 2000 was a leap year but 2100 will not be.