48-hour week and Working Time checker

The reference period

Working time is averaged over a 17-week reference period by default. A collective or workforce agreement can extend it to 26 weeks, and in limited cases a written agreement can take it to 52. Within that window a worker can do a 60-hour week without breaching anything, as long as the average holds.

That flexibility is worth having. Employers who believe every week must sit under 48 hours end up either refusing useful overtime or, more often, quietly ignoring the rule altogether because it appears impossible to keep.

Regulation 4(6), and why leave shortens the period

The formula is (A + B) ÷ C: A is the hours worked in the reference period, B is the hours worked in the days immediately after it that replace any excluded days, and C is the number of weeks. Excluded days are annual leave, sick leave, maternity and other statutory leave.

The practical effect is that excluded days shorten the period rather than dilute the average. Sixteen 50-hour weeks plus a week of annual leave averages 47.1 hours if you treat the leave as a zero, which looks compliant, and 50 hours once the leave is excluded, which is not. The tool asks for the excluded days for exactly this reason.

What an opt-out does, and what it does not

An individual opt-out removes the 48-hour average and nothing else. It has to be in writing, signed freely, and the worker can withdraw it on at least 7 days notice (up to 3 months if that was agreed). It cannot be a condition of getting shifts, and a worker who refuses must not be treated worse for refusing.

Everything else survives it: the 20-minute rest break, 11 hours of daily rest, 24 hours of weekly rest, the night-work limits, and 5.6 weeks of paid annual leave. An opt-out is a narrow document that is routinely treated as a general permission.

Night workers have two different rules

A night worker, someone who normally works at least 3 hours between 23:00 and 06:00, must not average more than 8 hours in each 24-hour period across the reference period. Where the work involves special hazards or heavy physical or mental strain, that 8 hours becomes an absolute cap in any 24 hours: no averaging, no opt-out.

Night workers must also be offered a free health assessment before starting night work and at regular intervals afterwards. The offer has to be recorded even when it is declined, and it is usually the first thing an inspector asks to see.

Under-18s are outside all of this

Young workers are limited to 40 hours a week and 8 hours a day, with no averaging in their favour and no opt-out available. There is no signature anybody can produce that makes a 45-hour week lawful for a 17-year-old.