Guide · Updated November 2026 · How we check our numbers
Counting Days Between Dates: Calendar Days vs Business Days
"How many days until…?" sounds simple, but deadlines, contracts and leave requests often depend on exactly how the days are counted.
Calendar days
The usual method subtracts the start date from the end date. The start day counts as day 0. From January 1 to December 25, 2026 that gives 358 days. If a rule says to include both the first and last day, add 1 (359).
Business days
Business days skip Saturdays and Sundays. From Monday, November 2 to Friday, November 13, 2026 (both included) there are 10 business days, even though 12 calendar days pass. Public holidays are not skipped automatically, because they differ by country and employer — subtract them yourself.
Adding days to a date
To find a date in the future, add the days one month at a time. June 1, 2026 + 90 days: 29 days to June 30, 31 more to July 31 (60), and 30 more lands on August 30, 2026.
Adding months is different
Adding a month to January 31 is a special case: February has no 31st, so the result is February 28 (or 29 in a leap year). Our Month Calculator follows this "end of month" rule, which most banks and contracts use.
Quick tips
- Check whether your rule counts the first day, the last day, or both.
- For working-day deadlines, use business days and remove holidays.
- Time zones can change the date near midnight — use the local date that matters for your deadline.
Try the calculators
This guide is general information, not professional advice.