Many compensation policies and similar documents refer to wages for non-exempt employees in the context of a "week", a "pay week", a "pay period", "the schedule", an "overtime week", or some other ambiguous word or phrase. But the timeframe that matters under the federal Fair Labor Standards Act is a term-of-art: A "workweek". For instance, with few exceptions, FLSA overtime pay is due for a non-exempt employee's hours worked over 40 in a single workweek, which is not necessarily the same thing as the calendar week or an employee's scheduled week or pay period.

An FLSA workweek is a fixed, regularly-recurring period of 168 hours – that is, seven, consecutive, 24-hour periods – that the employer expressly adopts in order to maintain FLSA compliance. FLSA recordkeeping regulations require covered employers to select and document at least one such workweek. The workweek can be set to begin on any calendar day and at any time of day, but thereafter the employer must apply that workweek in complying with the FLSA.

If an employer has not designated and documented a workweek, or if it computes pay based upon some timeframe other than the applicable workweek, this can lead to non-compliance. As an illustration, for the overwhelming majority of employees whose overtime must be determined on a workweek basis, the FLSA's requirements are not satisfied by paying overtime based just upon the number of hours worked over 80 in a two-week period or upon worktime exceeding 86.67 hours in a semi-monthly period.

What the workweek is can also affect what pay is due to an employee who must be paid on a "salary basis" in order to qualify for a particular FLSA exemption. For example, the FLSA "salary basis" exemption principles say that the salary need not be paid for any workweek in which the employee performs no work. However, to decide whether these are the circumstances, one has to know what workweek applies to that employee in the first place.