The definition
Under federal law a workweek is a fixed and regularly recurring period of 168 hours — seven consecutive 24-hour days. Three things follow from that wording, and each one matters:
- Fixed. Once set, it stays set. It cannot be changed week to week.
- Recurring. It repeats indefinitely on the same schedule.
- 168 hours. Not "the calendar week", not "Monday to Friday". A complete seven days including the days you do not work.
Your employer chooses when it starts. It can begin on any day and at any hour — Sunday at midnight is common, but Thursday at 6am is equally valid. It does not have to match the calendar week, the pay period, or anyone else's workweek at the same company. Different employees can have different workweeks.
Why it decides your overtime
Federal overtime is calculated within a single workweek: hours over 40 in that period are paid at time and a half. So the boundary determines which hours belong together.
Consider someone who works 30 hours, then 50 hours, across two consecutive weeks. If those are two workweeks, the second one contains 10 overtime hours, and the fact that the first was quiet is irrelevant. Averaging the two to 40 each and paying no overtime is not permitted — and it is one of the more common wage violations.
The same logic explains why a Saturday shift might be overtime for one colleague and not another: if their workweeks start on different days, the same calendar Saturday falls in different weeks.
What your employer can and cannot do
Can: choose any start day and hour; set different workweeks for different employees or departments; change the workweek permanently, if the change is intended to be lasting.
Cannot: change it temporarily to dodge overtime in a particular week. A workweek altered specifically so that a long stretch of hours straddles the boundary and falls under 40 on both sides is not a valid change — the purpose is what makes it improper.
Cannot: average hours across two workweeks, even if the pay period covers both. A biweekly pay period contains two workweeks, and overtime is worked out separately in each.
The pay period is not the workweek
This is where most confusion starts. They are different things and they serve different purposes:
- The workweek is the unit for calculating overtime. Always seven days.
- The pay period is the unit for issuing payment. It can be a week, two weeks, half a month or a month.
A semimonthly pay period is especially awkward, because 15 days does not divide into workweeks. A workweek will routinely straddle two pay periods, and the employer still has to calculate overtime on the whole workweek — often paying part of it in the following cheque. If you are paid semimonthly and your overtime seems to arrive late, this is usually why.
How to find out what yours is
It should be in your employee handbook, your offer letter, or on your pay stub. If it is not, ask HR or payroll directly — it is not confidential, and employers are expected to be able to state it. If nobody can tell you, that is itself worth noting: a workweek that is undefined cannot have been applied consistently.
You can also infer it. Look at a pay stub covering a week you worked overtime and see which days the premium hours were attributed to. The boundary usually becomes obvious.
Why this tool asks about it indirectly
The timesheet calculator totals the seven days you enter and applies the over-40 threshold to that set. That is correct provided the seven days you enter are one workweek. If you enter Monday to Sunday but your workweek runs Thursday to Wednesday, the total is right and the overtime split is not.
So enter your actual workweek, not the calendar week — starting on whichever day yours begins.