What Is a Weekday?
Definition
Weekday: One of the five days from Monday to Friday. ISO 8601 starts the week on Monday and numbers the days from 1 (Monday) to 7 (Sunday); Saturday and Sunday are the weekend.
A weekday is one of the five days from Monday to Friday; Saturday and Sunday are the weekend. It differs from a business day: a public holiday that falls on a weekday is still a weekday, but it is not a business day. The date difference calculator’s business days are really weekdays.
Where it appears in the formulas
weekdays = days − Saturdays and Sundays. 1 January to 31 December 2026, end day included, is 365 days; less 104 Saturdays and Sundays, that leaves 261 weekdays. The calculation uses the ISO 8601 numbers: Monday is 1 and Sunday is 7, and days 1 to 5 are weekdays.
Two meanings in English
In English, “weekday” sometimes means any day of the week, as in “What weekday is 1 January?”. On this site it means Monday to Friday only. Turkish public holidays are listed in Law No. 2429; to find business days, take the holidays that fall on weekdays off the count.