How the days are counted
The calculator takes the end date minus the start date. From 1 January to 31 December 2026 that is 364 days, or 365 with the end date included. Which one you want depends on what you are counting:
| What for? | Include end date? | Example |
|---|---|---|
| Countdown, age in days, time since | No | Days until Christmas |
| Holiday, trip, sick days | Yes | Mon–Fri = 5 days |
| Rental or contract period | Yes | 1 Jan – 31 Dec = 365 days |
| Deadlines ("within 14 days") | Usually no | Notice on 1 Oct → 15 Oct |
Adding days, weeks or months to a date
1 October 2026 + 100 days = Saturday, 9 January 2027
Weeks are counted as 7 days, months and years follow the calendar: 31 January + 1 month = 28 February, 29 February 2024 + 1 year = 28 February 2025.
Need to skip weekends and bank holidays? The working days calculator does that for the UK and US. To work out your last day after handing in notice, use the notice period calculator, and for paid leave the holiday entitlement calculator.
Days in each month
| Days | Months |
|---|---|
| 31 | January, March, May, July, August, October, December |
| 30 | April, June, September, November |
| 28 / 29 | February (29 in a leap year, e.g. 2028) |
FAQ
How do I count the days between two dates?
Enter a start date and an end date and the calculator shows the number of days straight away, plus the same span in weeks, months and years and how many of those days are weekdays. By default it counts like a calendar: 1 January to 2 January is 1 day. Tick "Include the end date" if the last day should count too, for example for a holiday or a rental period.
Is the start date or the end date included?
Without the tick, the result is the plain difference: the start date counts, the end date does not. With the tick both days count, so Monday to Friday is 5 days instead of 4.
What date is 100 days from today?
Switch to "Add or subtract", today is already filled in, enter 100 and you get the date with the weekday, ISO week number and day of the year. For a date in the past, enter a negative number such as -30.
What is 31 January plus one month?
There is no 31 February, so the calculator lands on the last day of the month: 28 February, or 29 February in a leap year. Weeks are always counted as 7 days.
Does it take off bank holidays?
No. "Weekdays (Mon–Fri)" only removes Saturdays and Sundays. To also take off UK bank holidays or US federal holidays, use the working days calculator.
How many days are in a year?
365 days, or 366 in a leap year. Leap years are years divisible by 4, except whole centuries that are not divisible by 400. The next leap year is 2028.
Legal basis and sources
For information only. Your contract or specific circumstances may change the result.