A typical, full-time work week consists of no more than 40 hours per week, usually from 9 a.m. until 5 p.m., as defined by the U.S. Department of Labor. Any extra hours are subject to overtime pay.

The Fair Labor Standards Act requires that overtime hours earn at least 1 1/2 times the pay of normal hours. The FLSA also requires that payment cannot be determined before knowing how many hours are to be worked, in effect prohibiting a flat salary. Under the provisions of the law, however, this only applies to full-time or part-time jobs, and not to self-employment or freelance work, according to the U.S. Department of Labor.

The act further defines hours of employment to be those hours for which an employee must be present at his job, states the U.S. Department of Labor. Work undertaken voluntarily (for instance, a software engineer writing a program outside of work hours) does not count toward the 40-hours-weekly cap. Waiting time, during which an employee is at his place of employment but not doing his job (for instance, a fireman waiting for an emergency) does still count towards the 40 hour maximum and is still billable. On-call time, during which an employee is not doing his job nor waiting for his job at his place of work, is not usually counted, although in some cases it may be.