The core rule — weekdays only, both endpoints included
A business-day count between two dates includes both the start and end date if they fall on a weekday, and simply excludes every Saturday and Sunday in between. It's a count of calendar weekdays, not a count tied to any specific company's actual working calendar — two people 10 calendar days apart both get the same business-day answer regardless of which country or industry they work in.
A worked example — spanning full weeks
From Monday, 14 September 2026 to Friday, 25 September 2026 (12 calendar days, inclusive): that's exactly 2 full 7-day weeks plus nothing left over, giving 10 business days and 2 weekend days. Because both weeks are "clean" (Monday-to-Friday), the business day count is simply 5 × 2 = 10 with no partial-week arithmetic needed.
A worked example — spanning a single weekend
From Friday, 11 September 2026 to Monday, 14 September 2026 (4 calendar days, inclusive): that's Friday, Saturday, Sunday, Monday — 2 weekdays (Friday and Monday) and 2 weekend days (Saturday and Sunday), giving 2 business days. This is the case people most often get wrong by mental math — it "feels" like 4 days of gap, but only 2 of those days are actually weekdays.
What this calculation deliberately does not account for
Public holidays are not excluded, and this is a deliberate choice, not an oversight — national holidays differ by country, regional/state holidays differ within a country (India alone has different state-specific holiday calendars), and some organizations observe additional company-specific holidays on top of both. There is no single authoritative holiday list a generic calculator could apply correctly for every user, so a plain weekday count is presented as exactly what it is: business days by the Monday-Friday definition, before any holiday adjustment.
Adjusting the result yourself for holidays
If you know your specific holiday count within the date range, subtract it from the business-day result to get an accurate working-day estimate for your organization or region — e.g. a business-day count of 10 with 1 known public holiday inside that range becomes 9 actual working days. This one-step manual adjustment is more reliable than trusting a generic calculator's built-in holiday assumptions, which would inevitably be wrong for a meaningful fraction of users given how much holiday calendars vary.