The short answer
- Most date differences leave out the end date: Monday to Wednesday is 2 days.
- Counting both dates adds one day, which suits holidays and some contracts.
- Working days leave out weekends and bank holidays, which differ between the UK nations.
- Months vary from 28 to 31 days, so “months and days” answers are counted on the calendar, not by dividing by 30.
Counting the end date or not
- Monday to Wednesday
- 2 days
- Used for
- Ages, durations, countdowns, nights in a hotel
- Monday to Wednesday
- 3 days
- Used for
- Days of an event, leave booked, some contracts
A whole calendar year counted with both dates included, 1 January to 31 December, is 365 days. Without the end date it is 364. Always check which convention your situation needs.
Worked examples
| From | To | Days | Working days |
|---|---|---|---|
| 4 Oct 2026 | 25 Dec 2026 | 82 | 59 |
| 31 Jan 2026 | 15 Mar 2026 | 43 | 30 |
| 21 Dec 2026 | 4 Jan 2027 | 14 | 7 |
| 1 Jan 2027 | 31 Dec 2027 (inclusive) | 365 | 253 |
- Days82
- Weeks and days11 weeks, 5 days
- Months and days2 months, 21 days
- Weekend days23
Over Christmas, from 21 December 2026 to 4 January 2027, there are 14 days but only 7 working days, because three bank holidays fall in the period: Christmas Day, the Boxing Day substitute on 28 December, and New Year’s Day.
Why months are tricky
Adding a month moves to the same day number in the next month, unless that month is shorter. From 31 January, one month later is 28 February (29 in a leap year). So 31 January to 15 March 2026 is 1 month and 15 days, even though it is 43 days.
Monthly payments and notice
Banks and contracts usually treat a month as a calendar month. A notice period of one month given on 31 January normally ends on 28 or 29 February, not 2 March.
Working days
Working days are Monday to Friday, less bank holidays. The calculator uses the bank holidays for England and Wales, Scotland or Northern Ireland. Some organisations also close between Christmas and New Year, or treat other days as non-working, so their count may differ.
| Nation | 2026 | 2027 |
|---|---|---|
| England and Wales | 253 | 253 |
| Scotland | 252 | 252 |
| Northern Ireland | 251 | 251 |
Adding days to a date
| Add | Result |
|---|---|
| 30 days | 3 November 2026 |
| 90 days | 2 January 2027 |
| 10 working days | 16 October 2026 |
| 1,000 days | 30 June 2029 |
Adding working days skips weekends and bank holidays. From 23 December 2026, 3 working days later is 30 December, because Christmas Day and the Boxing Day substitute are skipped.
Leap years
A leap year has 366 days, with 29 February. Years divisible by 4 are leap years, except century years not divisible by 400. So 2000 was a leap year, 2100 will not be, and the next leap year is 2028. Someone born on 29 February legally reaches a birthday on 1 March in non-leap years in England and Wales.
Everyday uses
- Counting down to a holiday, wedding or due date.
- Working out how long you have been in a job, for redundancy or holiday entitlement.
- Checking how many working days are left to meet a deadline.
- Planning a notice period or a tenancy end date.
- Calculating interest for a number of days on a loan or savings account.
Legal and official deadlines
Many legal time limits have their own rules. Some count calendar days, others clear days or working days, and some exclude the day of the event that starts the clock. Employment tribunal claims, for example, usually have a time limit of three months less one day from the act complained of. Always check the specific rule, and do not leave things to the last day.
Working out an age
For an age, put the date of birth as the start date and today as the end date, and leave out the end date. The years, months and days figure is the exact age. Someone born on 29 February 2000 was 26 years, 7 months and 5 days old on 4 October 2026, and had lived 9,714 days.
Doing it in a spreadsheet
In Excel or Google Sheets, subtracting one date from another gives the number of days. NETWORKDAYS counts working days and can take a list of bank holidays. DATEDIF gives whole years, months or days. Remember that NETWORKDAYS includes both the start and end dates.
Nights, days and stays
A hotel stay from Friday to Sunday is 2 nights but covers 3 days. Booking sites count nights, which is the same as days with the end date left out. Car hire is usually charged per 24-hour period, so a later return time can add a whole extra day. Travel insurance usually counts both the start and end dates of a trip.
Day counts for interest
UK banks usually work out savings and loan interest daily, dividing the annual rate by 365, even in leap years. The number of days is normally counted from the day money arrives up to, but not including, the day it leaves. That is the same as the calculator’s default setting, so you can use it to check interest for a period.
- Daily interest: £10,000 × 4% ÷ 365£1.10
- Days82
Clock changes and time zones
The calculator works in whole days, so clock changes do not affect the result. In hours, the day the clocks go forward in March has 23 hours and the day they go back in October has 25. For international deadlines, check which time zone applies, as a UK date can already be tomorrow in Asia or still yesterday in the Americas.
Pregnancy and baby dates
Pregnancy is counted from the first day of the last period, with a due date 280 days, or 40 weeks, later. Maternity leave can start from 11 weeks before the week the baby is due. The maternity pay calculator works out the key dates and pay.
School and term dates
School terms in England add up to 190 teaching days a year, set by councils or academy trusts. Term dates do not follow bank holidays exactly, so use your school’s calendar for exact counts. The calculator is useful for counting the days left until a holiday or an exam.