The off-by-one question
Nearly every argument about counting days is really about one question: does the last day count? From Monday to Friday is a gap of 4 days, but it touches 5 calendar days. Both answers are correct; they answer different questions:
- Exclude the end day (default) for gaps and intervals: nights in a hotel, days until a deadline, how long since an event.
- Include the end day for spans where both ends happen: days of a festival, length of a holiday, billing days.
Worked examples
Weekdays, working days and bank holidays
The weekdays figure strips out Saturdays and Sundays, which is what most people mean by working days day-to-day. It does not remove bank holidays, because those depend on the country and the year. A dedicated working days calculator with UK bank holidays baked in is on the Hopi roadmap; until then, subtract any bank holidays in your range from the weekdays figure.
Frequently asked questions
Is the end date included in the count?
By default no: Monday to Friday counts 4 days, the gaps between the dates. Tick include the end day to count Monday to Friday as 5 days, which is what you want for durations like hotel nights versus days of an event.
What is the difference between days and weekdays?
Days counts every calendar day including weekends. Weekdays counts Monday to Friday only. Note that weekdays still includes bank holidays, since those vary by country and year.
Why do people get off-by-one errors counting days?
Because counting the gap and counting the days are different questions. From the 1st to the 3rd is a gap of 2 days, but touches 3 calendar days. Decide which question you are asking, then set the include-the-end-day toggle to match.
Can I count between dates years apart?
Yes. The calculator handles any range and accounts for leap years automatically, so the gap between dates decades apart is exact.
How do I count working days excluding bank holidays?
The weekdays figure here excludes weekends only. For a count that also skips UK bank holidays, use a working days calculator, which is on its way to Hopi.