How business days are counted
A business day is a day when banks and government offices in that country normally work. Two inputs decide it: the local weekend and the local holiday list.
The weekend is not Saturday and Sunday everywhere
Saudi Arabia rests on Friday and Saturday. So does Israel, where Saturday is the main rest day and Friday is a rest day in most official calendars. A Friday deadline counted on US rules lands one working day late in Riyadh.
The United Arab Emirates shows why old data is dangerous. It moved its weekend from Friday-Saturday to Saturday-Sunday in January 2022. A dataset older than that change gives the wrong answer for the UAE on every single Friday, quietly.
When a holiday falls on a weekend
| Country | Rule | 2026 example |
|---|---|---|
| US | Observed on the Friday before or Monday after | 4 July is a Saturday; observed Friday 3 July |
| GB | Substitute day, usually the next Monday | Boxing Day is a Saturday; substitute Monday 28 December |
| DE | No substitute in most cases | A holiday on a Sunday is simply lost that year |
What the API stores
- Weekend rule per country, as weekday numbers.
- Holidays as observed dates, so counting never has to guess a substitution rule at query time.
- A reason on every negative answer: weekend, or holiday with its name.
Regional weekends exist too. Some Malaysian states rest on Friday and Saturday while the federal rule is Saturday and Sunday. v1 is country-level only, and it says so wherever a regional rule could change an answer.