How to Count Days Between Dates (Inclusive and Business Days)
Count the days between two dates correctly: when to include the start or end date, how to count business days, legal deadlines, and month arithmetic traps.
By Awais, Founder and editor-in-chiefPublished
To count the days between two dates, subtract the earlier date from the later one. From 1 March to 31 March is 30 days. If you need to count both the first and last day, as you would for days of leave or the days of a visa stay, add 1: that gives 31 days.
Most date mistakes come from not knowing which of those two answers a rule wants. This guide explains inclusive and exclusive counting, business days, how courts and visa rules count, and the month arithmetic traps that catch spreadsheets.
Exclusive vs inclusive counting
Exclusive counting (the default “difference”) counts the steps from one date to the next. It answers “how many days later is it?” or “how many nights?”.
Inclusive counting counts every calendar day touched, including both the start and the end. It answers “on how many days did this happen?”.
Inclusive days = end date − start date + 1
| Situation | Usually counted | 1 March to 31 March |
|---|---|---|
| How many days later? | exclusive | 30 |
| Hotel nights | exclusive | 30 nights |
| Days present, days of leave, days of a course | inclusive | 31 days |
| Days of stay for a visa rule | inclusive | 31 days |
When a form or contract does not say which method it uses, look for words like “from … to … inclusive”, “between” or “within”, or ask.
Counting by hand
Break the period into the rest of the first month, any full months, and the days in the last month.
Example: 15 August 2026 to 21 October 2026.
- 15 August to 31 August: 31 − 15 = 16 days
- September: 30 days
- 1 October to 21 October: 21 days
Total: 16 + 30 + 21 = 67 days (exclusive). Counting both 15 August and 21 October, it is 68 days.
Remember the month lengths (30 days have September, April, June and November; February has 28, or 29 in a leap year; the rest have 31). Leap years come every four years, except century years not divisible by 400, as Microsoft’s leap year explainer sets out. The date calculator does all of this automatically and lets you choose whether to include the end date.
Business days
Business days (working days) usually exclude Saturdays, Sundays and public holidays. Which days count as the weekend, and which holidays apply, depends on the country and sometimes the employer.
Spreadsheets count business days inclusively. Microsoft’s NETWORKDAYS documentation describes it as returning the number of whole working days between a start and end date, excluding weekends and any holidays you list; its own example counts both end dates.
Example: December 2026 has 23 weekdays (Monday to Friday). Christmas Day falls on Friday 25 December, so if it is a holiday where you work, December has 22 business days.
To count by hand: count full weeks (5 business days each), add the weekdays in the leftover days, then subtract holidays that fall on weekdays.
How legal deadlines count days
Courts and laws often set their own counting rules, and the details matter. In US federal civil cases, Rule 6(a) of the Federal Rules of Civil Procedure says that for periods stated in days you:
- exclude the day of the event that triggers the period
- count every day, including intermediate Saturdays, Sundays and legal holidays
- include the last day, but if it falls on a Saturday, Sunday or legal holiday, the period runs until the end of the next day that is not one of those
Example: an order is served on Friday 11 December 2026 and you have 14 days to respond. Day 1 is 12 December, so day 14 is Friday 25 December, Christmas Day, a legal holiday. The next two days are a weekend, so the deadline moves to Monday 28 December 2026.
Other courts, agencies and countries use different rules. Treat this as an example of how precise legal counting is, not as advice for your case; always check the rules that apply to you.
Visa stays: the Schengen 90/180 rule
The Schengen area allows many visitors to stay up to 90 days in any 180-day period. The EU’s short-stay calculator page explains that you count back 180 days from each day of your stay and the total must not exceed 90. The Schengen Borders Code counts the date of entry as the first day of stay and the date of exit as the last.
So a trip from 1 June to 10 June uses 10 days, not 9. Inclusive counting is easy to forget here, and an overstay of even one day can cause problems.
Month arithmetic traps
“One month later” is not always the same date
Adding a month to 31 January gives a date that does not exist, “31 February”. Software and people handle this differently; many tools move it back to the last day of February (28 February in 2027, 29 February in 2028). Then adding another month to 28 February gives 28 March, not 31 March, so repeated additions drift. When the exact date matters, add months to the original date each time, not to the previous result.
“30 days” and “1 month” are different
From 21 October 2026, 30 days later is 20 November 2026, while one month later is 21 November. Ninety days later is 19 January 2027, not 21 January. Contracts, notice periods and free trials can use either, so read the wording.
Days are not always 24 hours
In places that use daylight saving time, the day the clocks change is 23 or 25 hours long. In most of the United States, clocks go back on Sunday 1 November 2026, so that day has 25 hours. If you are counting hours across that weekend, use the time calculator or count in the local time zone carefully.
Years are not always 365 days
2026 has 365 days; 2028, a leap year, has 366. “One year” from 29 February 2028 runs into the same problem as month ends, which is why birthday maths has special rules. Our guide on calculating your exact age covers leap-day birthdays.
Quick checklist
- Decide whether the start date, end date or both count.
- For business days, confirm the weekend days and the holiday list.
- For legal or visa deadlines, follow the exact rule in the law or official guidance.
- Watch month ends, leap years and daylight saving changes.
- Check your answer with the date calculator, or the age calculator for birthdays.
FAQ
Do you count the first day when counting days?
It depends on the purpose. A simple difference between dates excludes the start date. Counts of days present, days of leave or days of stay usually include both the first and last day, so add 1.
How many days are there between two dates including both?
Subtract the earlier date from the later date and add 1. From 1 March to 31 March is 30 days apart, or 31 days counting both dates.
How do I count business days between two dates?
Count the weekdays from the start to the end date, then subtract any public holidays that fall on those weekdays. Spreadsheet functions such as NETWORKDAYS include both the start and end dates.
What date is 30 days from today?
Add 30 to today’s day number and carry into the next month as needed. From 21 October 2026, 30 days later is 20 November 2026, because October has 31 days.