How to use the date calculator
- Pick what you needBetween counts the days from one date to another, Add / subtract finds the date a number of days, weeks or months away, and Workdays counts Monday to Friday only.
- Enter the datesType them or use your browser’s date picker. The start date begins as today and the end date 30 days later; press Today to jump back to the current date at any time.
- Decide on the end dateSwitch on Include end date when both the first and the last day count, for example a hotel booking you pay for per night versus a festival you attend each day.
- Read the resultThe total updates instantly, split into years, months and days, into weeks, and into workdays. The calendar shows the final month with the counted days shaded.
Include the end date or not?
From Monday to Friday is 4 days if you count the gaps between the dates, and 5 days if you count every calendar day the period touches. Both answers are right; they measure different things. The default here counts gaps, the same way you would say that Friday is four days after Monday.
| Situation | End date | Example |
|---|---|---|
| Countdown | Excluded | From 1 June to a 10 June launch: 9 days to go. |
| Nights in a stay | Excluded | Check in 3 July, check out 7 July: 4 nights. |
| Rental or lease | Usually included | A lease from 1 March to 31 March covers 31 days of use. |
| Contract or notice period | Check the wording | “Within 30 days of” and “by the 30th day after” can differ by one day. |
| Leave or event days | Included | Holiday from Monday to Friday uses 5 days. |
Adding months and the month-end rule
Days and weeks are fixed lengths, so adding them is simple: 2 weeks is always 14 days. Months are not. Adding one month keeps the same day number in the next month, so 15 January plus one month is 15 February.
The awkward cases are days that don’t exist in the target month. 31 January plus one month has no 31 February to land on, so the result moves back to the last day of February: the 28th, or the 29th in a leap year. 31 August plus one month gives 30 September. This is the same convention most banks, spreadsheets and billing systems use for monthly due dates.
Because of this, adding months is not always reversible: 31 January plus one month is 28 February, but 28 February minus one month is 28 January. When an exact number of days matters, such as a 90-day notice period, add days instead of months.
Workdays, public holidays and leap years
Workdays here are Monday to Friday. Public holidays are not removed, because they differ by country, region and even employer, and they move from year to year. To get business days, take the result and subtract the holidays that fall on weekdays inside your range. A typical four-week month has 20 workdays; months with 31 days usually have 21 to 23.
Leap years add 29 February and are handled automatically. A year is a leap year if it divides by 4, except century years, which must also divide by 400. So 2028 is a leap year, 2100 is not, and 2000 was. That is why 28 February to 1 March is 2 days in 2028 but only 1 day in 2027.
Worked examples
How old is someone in days?
A child born on 12 March 2024 is, on 28 September 2026, 930 days old, which the calculator also shows as 2 years, 6 months and 16 days. Use Between dates with the birth date as the start and leave the end date excluded, the same way ages are normally counted.
A 90-day deadline versus three months
Adding 90 days to 1 October 2026 gives Wednesday 30 December 2026. Adding three months to the same date gives 1 January 2027, two days later. When a document says “90 days”, count days; when it says “three months”, count months, because the two are rarely the same.
A notice period that ends in February
Three months’ notice given on 30 November 2026 runs to 28 February 2027. February has no 30th, so the month-end rule moves the date back to the last day of the month.
Workdays in a quarter
From 1 January to 31 March 2027, with the end date included, there are 90 calendar days and 64 workdays. New Year’s Day falls on a Friday in 2027, so where it is a public holiday the real figure is 63, and one fewer for each further holiday in the quarter.
Handy date spans at a glance
Round numbers of days rarely line up with months, which is where most planning mistakes come from. These conversions are worth knowing by heart.
| Span | Days | Weeks and days | Good to know |
|---|---|---|---|
| 1 month | 28 to 31 | 4 weeks, 0 to 3 days | Only February in a common year is exactly 4 weeks. |
| 30 days | 30 | 4 weeks, 2 days | Equals one calendar month in only four months of the year. |
| 90 days | 90 | 12 weeks, 6 days | Three calendar months run from 89 to 92 days. |
| 180 days | 180 | 25 weeks, 5 days | Six calendar months run from 181 to 184 days in a common year. |
| 1 year | 365 or 366 | 52 weeks, 1 or 2 days | Why a date moves one weekday later each year, two after 29 February. |
| 1,000 days | 1,000 | 142 weeks, 6 days | From 1 January 2026 that is 2 years, 8 months and 26 days. |
Limits worth knowing
- Historical dates. All dates use the Gregorian calendar, extended backwards. Countries adopted it at different times: much of Catholic Europe in 1582, Britain and its colonies in 1752, when 3 to 13 September were skipped. Day counts that cross those changes won’t match records kept under the older Julian calendar.
- Weekends are Saturday and Sunday. Where the working week runs differently, for example with a Friday and Saturday weekend or a six-day week, the workday figure does not apply as shown.
- No times of day. Every date is a whole day. For durations in hours, such as a flight across time zones or a 48-hour return window that starts at a specific time, count the hours separately.
- Years 1 to 9999. That is the range browser date fields accept, and results that would fall outside it are not shown.
Questions
How many days are there in a year?
A common year has 365 days and a leap year 366. Over the full 400-year cycle of the Gregorian calendar the average is 365.2425 days, which is why the calculator always counts real calendar days instead of multiplying years by 365.
How do I count down to a date?
Choose Between dates, press Today for the start and enter the event as the end date. Leave “Include end date” off: the result is the number of midnights still to pass, which is how most countdowns are shown.
Can I calculate a date in the past?
Yes. In Add / subtract, use the Add / Subtract switch to choose the direction; the amount itself is always a positive number. In Between dates, an end date earlier than the start gives the distance counted backwards, and the tool tells you so.
How many working days are in a year?
A common year has 260 or 261 weekdays and a leap year 260 to 262, depending on which weekday 1 January falls on. Subtract your public holidays and paid leave for the days actually worked; with 10 holidays and 20 days of leave, that leaves around 230.
Does my time zone affect the result?
No. Dates are treated as whole calendar days, without a time of day, so time zones and daylight-saving changes cannot move a result by a day. Only the Today button uses your device’s clock, to find the current local date.
What does 90 days from today mean on a form?
Normally it means adding 90 days to today’s date, which is what Add / subtract does. Some rules count the first day as day one and end a day earlier, so if a deadline matters, check the exact wording or ask the issuer.