For a Monday to Friday worker there are either 260, 261 or 262 working days in a year. In a 1981 study the General Accounting Office (GAO) demonstrated this calendar cycle repeats over a 28 year period.
There are 7 times 260 working days, 17 times 261 working days and 4 times 262 working days over the 28 year cycle.
The year will have 260 working days when the first day of the year starts with a weekend (either a Saturday or a Sunday) and the last day of the year also ends on a weekend.
The year will have 262 working days when the first day of the year starts with a weekday and the last day ends on a weekday, and it’s a leap year.
Other combinations will give 261 working days per year.
[This cycle also gives us the payroll divisor of 52.1786 to convert a weekly wage to an annual salary].