How to use the date calculator
- Days between two dates: choose a start and an end date. You see the total number of days, the same span in weeks and in years, months and days, and how many of those days are working days and weekend days.
- Add or subtract time: choose a date, an amount and a unit to find a deadline, a due date or a date in the past. The result shows the weekday and ISO week number.
- To leave bank holidays or other days off out of the working days, open Holidays and other days offand list them, or add the England and Wales bank holidays with one click.
Results update as you change anything. Dates are worked out in your browser and are not sent anywhere.
How dates are counted
- Days between counts the start date but not the end date, unless you tick Include the end date. If the end date is before the start date, the dates are counted the other way round.
- Months at the end of a month: when a day does not exist in the target month, the last day of that month is used. 31 January plus one month is 28 February (29 February in a leap year), and 29 February plus one year is 28 February. The years, months and days between two dates follow the same rule, so adding the result to the start date always gives the end date.
- Working days are Monday to Friday, minus any dates you exclude. When adding working days, the start date itself is not counted, so Friday plus one working day is the following Monday.
- Each date is a whole day with no time of day, so daylight saving changes and time zones never shift a result.
Bank holidays
The bank holiday button adds the regular England and Wales bank holidays for the years you are counting, including substitute days when Christmas, Boxing Day or New Year’s Day falls at a weekend. Each line shows the holiday’s name, so you can check or remove any you do not need.
Limitations
- One-off bank holidays, such as those for jubilees and coronations, are not added automatically. CheckGOV.UK bank holidays and add them yourself. Scotland and Northern Ireland have different bank holidays.
- Weekends are always Saturday and Sunday. Countries with a different weekend are not supported yet.
- Years from 1 to 9999 are supported, using today’s Gregorian calendar throughout. Britain switched from the Julian calendar in 1752, so historical dates before then may not match old records.
- Numeric dates in the holiday list are read day first (25/12/2026), so US-style month-first dates are not accepted.
Frequently asked questions
Does “days between” count the start and end date?
By default the start date is counted and the end date is not, the same as subtracting one date from the other: Monday to Friday is 4 days. Tick Include the end date to count both, which is what you want for things like the length of a holiday or a hire period: Monday to Friday inclusive is 5 days.
How do I work out someone’s age?
Choose Days between two dates, enter the date of birth as the start date and today as the end date. The years, months and days figure is their exact age, and the total shows how many days old they are.
Are bank holidays taken off working days?
Only if you list them. Working days are Monday to Friday, minus any dates in Holidays and other days off. The Add England and Wales bank holidays button fills in the regular holidays for the years you are counting. Scotland and Northern Ireland have different bank holidays, such as St Andrew’s Day and St Patrick’s Day, so add those yourself.
What is an ISO week number?
ISO 8601 numbers the weeks of a year from 1 to 52 or 53. Weeks start on Monday, and week 1 is the week that contains the year’s first Thursday. So 1 January can fall in week 52 or 53 of the previous year, and 31 December can fall in week 1 of the next. Many European businesses and planning tools use ISO weeks.