The 48-hour week and the working time opt-out
It is an average over 17 weeks, not a weekly ceiling - and the opt-out covers that average and nothing else. Both halves of that sentence are routinely got wrong, in opposite directions.
A worker's working time, including overtime, must not exceed an average of 48 hours for each seven days, measured over a 17-week reference period (reg 4, Working Time Regulations 1998). A worker can agree in writing to disapply that limit. They can cancel with seven days' notice, the agreement can never require more than three months' notice, and the employer must keep an up-to-date record of who has opted out.
It is an average, not a cap
This is where most of the confusion lives. Regulation 4(1) does not prohibit a 55-hour week. It prohibits an average above 48 hours across the reference period, which is normally 17 weeks. A busy fortnight followed by quiet ones may be entirely compliant; a steady 50 hours every week is not, opt-out or no opt-out.
Two consequences follow:
- You cannot tell whether you are compliant by looking at one week. You need the running 17-week picture, per person.
- For someone employed less than 17 weeks, the reference period is simply the time since they started - so a new starter's average is calculated over a shorter, less forgiving window.
Certain absences are taken out of the calculation rather than counted as zero-hour weeks - annual leave, sick leave and maternity, paternity or adoption leave among them. That matters: counting a fortnight of holiday as two 0-hour weeks would flatter the average and hide a genuine breach.
Regulation 4(2) requires you to "take all reasonable steps, in keeping with the need to protect the health and safety of workers" to ensure the limit is met for each worker. Not to permit it, not to discourage exceeding it - to take steps. An employer who never looks at anyone's average has not taken reasonable steps, whatever the contract says.
What the opt-out actually disapplies
Only the 48-hour average. Everything else in the Regulations continues to apply in full:
- Daily rest and weekly rest.
- In-work rest breaks.
- The limits and health assessments applying to night work.
- Paid annual leave.
A signed opt-out is not a general waiver of working time rights, and treating it as one is a common and expensive mistake - particularly in sectors where the opt-out is issued as routine paperwork and then used to justify rosters that breach the rest rules instead.
Getting the agreement right
The agreement must be in writing and made by the individual worker. A collective or workforce agreement cannot opt people out of the 48-hour limit on their behalf. Making it a condition of getting or keeping a job, or treating someone worse for refusing, undermines the agreement and creates a separate problem of its own. In practice the risk is not coercion but drift: the opt-out slipped into a contract pack, signed unread by everyone.
An opt-out may cover a specified period or apply indefinitely (reg 5). But indefinite does not mean irrevocable. A worker can cancel by giving not less than seven days' notice in writing. If the agreement sets its own notice period that period applies - capped at three months. An agreement demanding six months' notice, or none at all, is not enforceable to that extent.
Regulation 4 requires the employer to maintain up-to-date records of workers who have agreed to disapply the limit. "Up to date" is the operative phrase: a folder of signed forms from four years ago, with no note of who has since cancelled or left, is not a record of who has opted out today.
Young workers cannot opt out at all
Young workers - broadly those above school leaving age and under 18 - are limited to 8 hours a day and 40 hours a week (reg 5A), and there is no opt-out from those limits. Where a young worker has more than one job, the hours are aggregated across employers - so a Saturday job elsewhere counts against your 40. If you employ under-18s, that aggregation question belongs on the starter form, because you cannot comply with a limit you have not asked about.
What good practice looks like
- Track hours per person with a rolling 17-week average, not a weekly total.
- Hold the opt-out separately from the contract, so signing it is a distinct decision.
- Keep a live list of who has opted out, and remove people when they cancel or leave.
- Review anyone approaching the average, whether or not they have opted out - the health and safety duty does not disappear because someone signed a form.
- Flag under-18s and ask about other employment.
The opt-out agreement template covers the wording, and the rolling rota template has the rest checks built in.
Keep reading: All 66 HR guides · 30 free templates · 24 calculators
A 17-week average you can actually see
CoDash records hours worked per person and keeps the running average where a manager will notice it - along with who has opted out and when they signed, so the record stays current instead of ageing in a folder.