How business days are counted

Ask three professionals how many business days sit between two dates and you can get three different answers — each correct under its own convention. This is the argument, settled on one page.

Convention 1: Inclusive of both ends (Excel NETWORKDAYS)

Excel's NETWORKDAYS(start, end, holidays) counts every workday from start to end including both, skipping Saturdays, Sundays and any dates in the holidays argument. A task running Wednesday to Wednesday counts both Wednesdays plus the five workdays between: six. This matches how people think about durations — a Monday-to-Friday work week is five days, not four.

Convention 2: Exclusive of the start (payment terms)

Net-30 terms mean you have thirty days to pay — the day the invoice lands is not a payment day. Operations teams formalize this as "count from the next business day". The same Wednesday-to-Wednesday span now yields five: the anchor Wednesday is excluded. This is the counting you want for SLAs, dispute windows and "days from receipt" clauses.

Convention 3: The +1 compensation

Sheets without a NETWORKDAYS column breed a workaround: subtract the dates, then add 1 back. Numerically it matches the inclusive count — but it inherits a trap. Plain date subtraction across a month boundary, daylight-saving transitions (in tools that count hours), or a mis-typed format can each silently shift the base value. If you see +1 in someone's formula, ask how the base subtraction is computed.

The holiday wildcard

Every convention above still has to pick a holiday list. U.S. federal holidays (OPM schedule, observed dates) are the most common default; state holidays add days like Patriots' Day; companies add floating days. Two ranges that look identical can differ by one business day per holiday they cross — over a Thanksgiving week, that is the difference between "Thursday delivery" and "Friday".

Which one should you use?

Whichever the document says. Failing a document: deadlines exclude the start day; durations include both ends; and whenever money or a dispute rides on the answer, compute all three with the business days calculator and raise the ambiguity before the deadline, not after.

Common questions

Why does Excel's NETWORKDAYS include both endpoints?

It is designed for duration questions: a task running Monday to Friday covers five workdays, so both bookends count. Payment terms ask a different question — "how many days do I have to pay" — where the receipt day is not a payment day. Same shape, different intent, different count.

What does the law say?

Often less than you would hope. Many jurisdictions default to calendar days unless a statute or contract says otherwise, and contracts routinely say nothing. Courts generally apply the contract's own definition when one exists — which is why getting it into writing matters more than winning an argument about the "right" method.

How do leap years and holidays interact?

Holidays are excluded only where they fall on a weekday in your range; a holiday on a weekend removes nothing (its observed date does). Leap day counts as a workday if it is not a holiday — it never is, in the U.S. federal calendar.

Last updated 2026-11-04 · Calculations follow the full leap-year rule (including the year 2100 exception).