Working days depend on whose calendar you are using

"Five working days" sounds like a fact. It is two conventions wearing a number.

The first convention is which days of the week are not working days. The second is which dates are days off on top of that. Neither can be worked out from a pair of dates, because neither is a property of the calendar — they are properties of a country, an industry and an organisation, and they vary across all three.

The counting method

The naive approach is to walk day by day and add one for each Monday through Friday. That works, and it is slow over long spans. The direct method uses the fact that every whole week contains exactly five weekdays, whichever day the week happens to start on.

1. Take the span in days, counting both end dates: end − start + 1.
2. Whole weeks in that span: span ÷ 7, rounded down. Each contributes 5.
3. Walk the leftover days — at most six of them — starting from the weekday of the start date, and add one for each that is not a Saturday or Sunday.

No loop longer than six steps, and no chance of drifting.

Worked: July 2026

From 1 July 2026 to 31 July 2026, both ends counted.

• Span: 31 days.
• Whole weeks: 31 ÷ 7 = 4, remainder 3. Weeks contribute 4 × 5 = 20.
• 1 July 2026 is a Wednesday, so the three leftover days are Wednesday, Thursday and Friday — all three count.
• Total: 20 + 3 = 23 weekdays.

Twenty-three, before anybody subtracts a single day off.

The leap-year and month-end case

February is where month-length assumptions go to die, and a leap year doubles the effect.

• February 2024, 1st to 29th: span 29 days, so 4 whole weeks (20) plus 1 leftover day. The 1st was a Thursday, which counts. Total 21 weekdays.
• February 2026, 1st to 28th: span 28 days, exactly 4 whole weeks and no remainder at all. Total 20 weekdays.

Same month, one extra calendar day, one extra working day. And notice February 2026 needs no remainder walk whatsoever — a 28-day span is four clean weeks, so it always yields 20, whichever day it starts on. That is a small, real fact you can carry around.

Inclusive, because that is what a working-day count means

The weekday count deliberately includes both end dates. Monday 2 March 2026 to Friday 6 March 2026 is 5 working days, not 4 — because you work on the Monday and you work on the Friday.

That is the opposite convention to a plain date difference, which gives 4 for the same pair. Both are right for their own question, and the reason they differ is worth holding on to: a difference measures distance, a working-day count measures days you are present for.

The two things no calculator can know

Which days are the weekend. Monday to Friday is common and it is not universal. Some countries run a different pair of rest days, some organisations run a six-day week, and plenty of shift patterns have no weekend at all. A tool that assumes Monday to Friday is making an assumption on your behalf, and you should know it is making one.

Which dates are days off. Public holidays differ by country, by region within a country, and by employer — and some of them move from year to year rather than sitting on a fixed date. On top of that, organisations close on dates that are nobody's public holiday, and stay open on dates that are. There is no way to derive this list; somebody has to supply it.

So the honest procedure is: count the weekdays, then subtract the days off from your own list, then say which list you used.

What the tool does, and does not

The free Business Days tool counts Monday through Friday between two dates, inclusive of both ends, using the whole-weeks method above. It does not deduct holidays of any kind, and it does not offer an alternative weekend — it is the weekday count and nothing more.

That is a limit stated on purpose rather than a gap. A calculator that quietly applied one country's day-off list would give a confident wrong answer to everybody else, and a wrong lead time is worse than an obviously incomplete one. Take the 23, subtract your own days off, and write down which calendar you subtracted from.