Days between two dates, also as years, months and days, weeks and hours, plus business days after weekends and your own holidays.
From Sun 27 Sep 2026 to Sat 26 Dec 2026 is 90 days — 0 years, 2 months, 29 days, or 12 weeks and 6 days. Of those, 65 days are business days.
N counts days from 1 January 1970 in the proleptic Gregorian calendar.
2 whole months from Sun 27 Sep 2026 reach Fri 27 Nov 2026; 29 days more reach Sat 26 Dec 2026.
Months are counted from the start date's day of the month. When that day doesn't exist in a month (the 31st in April, the 29th–31st in February), the month's last day is used.
Weekend: Saturday and Sunday. Holidays that fall on a weekend are not subtracted twice.
Each date is turned into a day number, the count of days since 1 January 1970 in the Gregorian calendar, and the difference of the two numbers is the number of days between them. The years, months and days figure steps whole months forward from the start date; when that day of the month doesn't exist, the month's last day is used. Business days are the total minus weekend days minus any listed holidays that fall on working days.
People use it for notice periods, visa and residence stays, project schedules and interest periods. From 31 January to 1 March 2024 is 30 days, which reads as 1 month and 1 day because one month after 31 January is 29 February in a leap year.
The end date is left out by default, the same convention as subtracting dates in a spreadsheet. Switch on "Include the end date" when both the first and last days count: leave from Monday to Friday is 5 days, not 4.
Split the span at month boundaries: count the days left in the start month, add the full months in between, then add the day of the end month. From 14 March to 9 August 2026:
The total is 17 + 122 + 9 = 148 days, the figure the calculator gives, which is also 4 months and 26 days. This method counts 15 March through 9 August; the calculator's default counts 14 March through 8 August. Both leave out one end, so both give 148.
A span that crosses 31 December works the same way. From 20 November 2025 to 6 February 2026, 20 November is day 324 of a 365-day year, so 365 − 324 = 41 days of 2025 follow it, and 6 February is day 37 of 2026: 41 + 37 = 78 days.
The day number of each month's first and last day turns most counts into one subtraction: find each date's day of the year and subtract. The leap-year column applies to 2024, 2028 and every other year divisible by 4, except century years not divisible by 400.
| Month | Days | 1st is day (common year) | Last day is day (common year) | 1st is day (leap year) | Last day is day (leap year) |
|---|---|---|---|---|---|
| January | 31 | 1 | 31 | 1 | 31 |
| February | 28 (29) | 32 | 59 | 32 | 60 |
| March | 31 | 60 | 90 | 61 | 91 |
| April | 30 | 91 | 120 | 92 | 121 |
| May | 31 | 121 | 151 | 122 | 152 |
| June | 30 | 152 | 181 | 153 | 182 |
| July | 31 | 182 | 212 | 183 | 213 |
| August | 31 | 213 | 243 | 214 | 244 |
| September | 30 | 244 | 273 | 245 | 274 |
| October | 31 | 274 | 304 | 275 | 305 |
| November | 30 | 305 | 334 | 306 | 335 |
| December | 31 | 335 | 365 | 336 | 366 |
For 14 March to 9 August 2026, 9 August is day 213 + 8 = 221 and 14 March is day 60 + 13 = 73, and 221 − 73 = 148. The week number and day of the year calculator gives the day number of any date directly.
Take 3 to 10 March 2026, Tuesday to Tuesday. Subtracting the dates gives 7. Counting both ends gives 8. Counting neither end gives 6, which is what "clear days" means. Laws and contracts pick one of these, and the wrong one moves a deadline by a day.
| Convention | Start date | End date | 3 to 10 March 2026 | Where it is used |
|---|---|---|---|---|
| Subtraction (calculator default) | Counted | Left out | 7 days | Spreadsheet date subtraction; hotel nights |
| Inclusive | Counted | Counted | 8 days | Leave booked from one date to another; rota counts |
| Clear days | Left out | Left out | 6 days | Notice periods for UK company meetings |
| US federal court deadlines | Left out | Counted | 7 days | Filing periods in days |
The UK Companies Act 2006, s.360 excludes both the day notice is given and the day of the meeting. A private company's general meeting needs at least 14 days' notice under s.307, so notice given on 1 June 2026 allows a meeting on 16 June at the earliest. In the calculator, 1 June to 16 June is 15 days, which counts 1 June; take off 1 for the day the notice was given and 14 clear days remain.
US federal courts use Federal Rule of Civil Procedure 6(a): exclude the day of the triggering event, count every day including weekends and holidays, and include the last day, but if that day is a Saturday, Sunday or legal holiday the period runs to the next day that is not. A 10-day period triggered on Wednesday 4 March 2026 would end on Saturday 14 March, so it moves to Monday 16 March. The add or subtract days calculator finds the end date from a start date and a number of days.
Business days are the total days minus weekend days minus holidays that fall on working days. The inclusive setting matters here too: a count of April 2026's working days needs "Include the end date" switched on, or Thursday 30 April is dropped and the count falls from 22 weekdays to 21. With the two Easter bank holidays in England and Wales, Good Friday on 3 April and Easter Monday on 6 April (gov.uk bank holidays), April 2026 has 20 working days.
Excel's NETWORKDAYS counts both the start and end dates. Microsoft's example returns 110 working days from 1 October 2012 to 1 March 2013, while the calculator's default gives 109 for the same dates because 1 March 2013, a Friday, is left out. NumPy's busday_count also leaves out the end date.
A holiday that falls on a weekend is not subtracted a second time. Over Christmas 2026 in England and Wales, 26 December is a Saturday and the Boxing Day bank holiday moves to Monday 28 December. Listing 25, 26 and 28 December and 1 January for the span from 24 December 2026 to 4 January 2027 removes 3 days, not 4, and leaves 4 business days. Scotland has a different list: for 2026 it includes 2 January, a one-off World Cup bank holiday on 15 June and St Andrew's Day on 30 November, has its summer bank holiday on 3 August rather than 31 August, and leaves out Easter Monday. To find the date a number of working days after a start date, use the working days deadline calculator.
A month is 28 to 31 days, so the months-and-days figure depends on where the span starts. The calculator steps whole months forward from the start date's day of the month, and when that day doesn't exist it uses the month's last day:
Two spans with the same number of days can therefore show different months and days. When a contract, loan or statute sets a period in days, use the total days; when it sets months, use the months figure and check the end-of-month case. The same logic runs the age calculator, which counts months from the day of birth.
Checked against: Python 3.8 datetime: (date(2024,3,1) − date(2024,1,31)).days = 30; dateutil.relativedelta (same end-of-month clamp) = 1 month 1 day; numpy.busday_count = 22
Checked against: Python 3.8 datetime difference = 366 days; dateutil.relativedelta = 1 year 1 day; numpy.busday_count = 262
Checked against: Python 3.8: date(2027,1,1) − date(2026,1,1) = 365 days; numpy.busday_count('2026-01-01','2027-01-01') = 261
Checked against: numpy.busday_count('2026-01-15','2026-02-15', weekmask='1111001') = 21
Subtract the earlier date from the later one using day numbers, which is what a spreadsheet does with =B1-A1. From 1 January to 31 December 2026 that gives 364 days; add 1 if the last day should count as well, giving 365. Counting on a calendar by months goes wrong at month ends and leap years, which day numbers handle automatically.
It includes the start date and leaves out the end date, so 1 to 3 March is 2 days, matching Excel date subtraction and Python's date arithmetic. Turn on "Include the end date" to count both, which makes 1 to 3 March 3 days. Contracts and statutes sometimes define their own rule, so check the wording when a deadline has legal effect.
2026 has 261 weekdays, Monday to Friday. England and Wales have 8 bank holidays in 2026, all on weekdays (gov.uk lists Boxing Day as Monday 28 December), which leaves 253 working days. For another country, paste its public holidays into the holidays box, one ISO date per line, and they are taken off the business-day count.
Months are counted from the start date's day of the month, and a day that doesn't exist in the target month becomes that month's last day. So 31 January plus one month is 29 February 2024, and 31 January to 1 March 2024 is 1 month and 1 day. Microsoft notes that Excel's DATEDIF with the "MD" unit may return a negative number, a zero or an inaccurate result, which this method avoids.
Divide the number of days by 7: the whole number is the weeks and the remainder is the extra days. 90 days is 12 weeks and 6 days, and a leap year's 366 days is 52 weeks and 2 days. Pregnancy is dated in the same weeks-plus-days form, written 12+6.
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 6 worked examples whose answers come from independent sources; for example, “Month-end start in a leap year” is checked against Python 3.8 datetime: (date(2024,3,1) − date(2024,1,31)).days = 30; dateutil.relativedelta (same end-of-month clamp) = 1 month 1 day; numpy.busday_count = 22.
ISO 8601-1:2019 — Date and time, representations for information interchange; Howard Hinnant — chrono-compatible low-level date algorithms (days_from_civil); NumPy busday_count (business-day counting convention: end date excluded).
6 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.
Exact age from a date of birth in years, months and days on any date, with the next birthday and age in months, weeks, days and hours.
The date a number of days, weeks, months, years or business days after or before a start date, with its weekday and the calendar days moved.
The deadline N business days after or before a start date, skipping weekends and the holidays you list, with the calendar days it spans.
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