Date Duration Calculator
InstantNewWork out the exact duration between two dates in years, months, and days, including total days, weeks, and business days. Add or subtract days from any date, and find the weekday and ISO week number for a given date.
Date Duration Calculator
Duration
0 y 0 m 30 d
Total days
30
Total weeks
4w 2d
Business days
21
Weekend days
9
How the math works
Days between = (end − start) ÷ 86,400,000 ms
Inclusive = add 1 day so the end date is counted
Add days = start ± N calendar days
ISO week = week starting Monday; week 1 holds the first ThursdayThe duration is measured in whole calendar days between the two dates at midnight, then grouped into years, months, and days (borrowing from the previous month where needed, so leap years and differing month lengths are handled correctly). Business days exclude Saturdays and Sundays. Enabling “Include end date” counts the final day itself, which is useful for billing periods and event durations.
What you can calculate
- Days between two dates: exact years, months, and days plus total days, weeks, and business days.
- Add or subtract days: find the date that falls a given number of days before or after a start date.
- Weekday & week number: see which day of the week a date lands on, its ISO-8601 week number, and its day-of-year.
Inclusive vs exclusive counting
By default the calculator counts the gap between the dates: from Monday to Wednesday is 2 days. Turning on “Include end date” counts both endpoints, giving 3 days — the convention used for things like hotel stays, rental periods, and project timelines.
Frequently asked questions
How do I count the number of days between two dates?+
Enter a start date and an end date. The calculator shows the duration as years, months, and days, plus the total number of days, weeks, and business days between them.
What is the difference between inclusive and exclusive day counting?+
Exclusive counting (the default) measures the gap between the dates, so Monday to Wednesday is 2 days. Inclusive counting adds the end date itself, giving 3 days — the convention used for hotel stays, rentals, and billing periods.
How are business days calculated?+
Business days count every day from Monday to Friday in the span and exclude Saturdays and Sundays. Public holidays are not deducted.
What is an ISO week number?+
The ISO-8601 week number runs from 1 to 52 or 53. Weeks start on Monday, and week 1 is the week containing the year's first Thursday. It is widely used in business, logistics, and European calendars.
How do I add or subtract days from a date?+
Switch to the Add / Subtract tab, pick a start date, choose add or subtract, and enter a number of days. The calculator returns the resulting date along with its weekday.
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