How to use the date calculator
- Days between dates: pick a start and an end date to get the number of days, plus the same span in weeks, months and years, working days and weekend days.
- Add or subtract: pick a date and add or take away days, weeks, months, years or business days. Useful for deadlines, notice periods and due dates.
How the days are counted
Days between = end date − start date
Including the end date = end date − start date + 1
By default the count doesn't include the end date, which is how most date maths works: from Monday to Tuesday is 1 day. Choose "include the end date" when you need every day of an event, such as a 3-day conference from Monday to Wednesday.
Worked example
From 1 January 2026 to 25 December 2026 is 358 days: 51 weeks and 1 day, or 11 months and 24 days. Of those, 256 are working days (Monday to Friday).
Adding 90 days to 30 October 2026 gives 28 January 2027.
Adding months: the end-of-month rule
Months have different lengths, so adding 1 month to 31 January lands on 28 February (or 29 in a leap year), the last day that exists. The calculator always uses the last day of the month in this case, which matches how most banks, spreadsheets and contracts handle it.
Need someone's exact age? Use the age calculator.
Frequently asked questions
Does it skip public holidays?
No. Business days skip Saturdays and Sundays only, because public holidays differ between countries and regions. Subtract any holidays that fall in your range.
How many days are there in a year?
365, or 366 in a leap year. Leap years are divisible by 4, except century years not divisible by 400. 2028 is the next leap year.
How many weeks are in a year?
52 weeks and 1 day, or 52 weeks and 2 days in a leap year.
Formulas checked 29 October 2026. How we test our calculators. Check important deadlines, hours and pay against the official rules and records that apply to you.