How to use it
- Pick the start date and the end date.
- Read the number of days, and below it the same span split into years, months and days, into weeks and days, and into months and days.
- Tick Include the end date when both the first and the last day should count, for example for a booking that runs through the last day.
How the difference is counted
Days are the plain difference between the two calendar dates. Dates are whole days, so time zones and daylight saving time do not change the answer.
Years, months and days count whole months from the start date first, then the days left. When a month is shorter than the start day, the month ends on its last day: one month after 31 January is 28 February (29 in a leap year). This is the same rule as in the age calculator.
Weeks are the days divided by 7, with the remainder shown as days.
Business days are the Mondays to Fridays in the span. Without the end date, the start date counts and the end date does not; with it, both count. Public holidays are not subtracted: the tool does not know which country’s calendar you use.
Worked example
From 1 January 2026 to 31 December 2026:
- 364 days, which is exactly 52 weeks;
- 1 January plus 11 months is 1 December, then 30 more days: 11 months and 30 days;
- 2026 starts on a Thursday, so its 52 full weeks hold 260 weekdays; the one extra day, Thursday 31 December, is the end date and is not counted: 260 business days.
With the end date included the span becomes 365 days, exactly 1 year, and 261 business days.
Common mistakes
- Off by one day. Counting “from Monday to Friday” can mean 4 days (the gap) or 5 (both days). Decide which you need and set the checkbox.
- Months are not all the same length. “3 months” from 30 November ends on 28 February in a common year, not after 90 days.
- Holidays. A business-day count that should skip Christmas or a national holiday needs those days listed: use the working days calculator.