The 48-hour working week and opting out : calculate what you are owed

• Most adult workers cannot work more than 48 hours a week on average, normally averaged over 17 weeks, unless they have a voluntary written individual opt-out.
• Your employer can ask you to opt out. They cannot sack you or treat you unfairly for refusing. You can cancel later (usually at least 7 days' notice, up to 3 months if your agreement says so).
• If you are under 18, the young worker limits are different: normally no more than 8 hours a day or 40 hours a week, and those young limits are not something you opt out of in the adult 48-hour sense.
• Employers must keep working-time records that show the 48-hour limit is respected (or that you have opted out). Acas says those records must be kept for 2 years.
• Long hours and unpaid minutes can also create a minimum wage problem. HSE (or the local authority) enforces many weekly-hours and night-limit rules; unpaid wages and NMW shortfalls are usually pursued through your employer, Acas Early Conciliation and, if needed, an employment tribunal or HMRC.
• For most pay claims today (September 2026), the tribunal limit is 3 months minus 1 day. From 1 October 2026, most claims become 6 months minus 1 day if the time limit starts on or after that date (Acas).

GOV.UK is blunt: you cannot work more than 48 hours a week on average, normally averaged over 17 weeks. The same page calls this the working time directive or Working Time Regulations rules.

Regulation 4 of the Working Time Regulations 1998 puts that into legal form: unless your employer has first obtained your agreement in writing, your working time (including overtime) in the applicable reference period must not exceed an average of 48 hours for each seven days. Employers must take all reasonable steps to protect health and safety and keep up-to-date records of workers outside the limit because of a written agreement.

The ceiling is an average, not a hard stop every calendar week. You can work more than 48 hours in one week if the average over the reference period stays at or under 48.

GOV.UK says average working hours are calculated over a "reference" period, normally 17 weeks. That can extend to a maximum of 52 weeks if agreed (for example by a trade union). Some jobs use different periods (GOV.UK examples include trainee doctors at 26 weeks and offshore oil and gas at 52 weeks). If you have worked for less than 17 weeks, regulation 4 uses the period since you started.

GOV.UK lists what counts towards the weekly maximum (among other things): job-related training; travel that is part of the job; working lunches; time working abroad; paid overtime; unpaid overtime you are asked to do; time on call at the workplace; time treated as working time under a contract; and home-to-work travel at the start and end of the day if you do not have a fixed workplace.

It does not count (among other things): on-call time away from the workplace; breaks when no work is done; travelling outside normal working hours; unpaid overtime you have volunteered for; holiday; and ordinary commuting if you have a fixed workplace.

Acas adds that working time is when you are at the employer's disposal and carrying out work activities, duties and training. If you have more than one job, GOV.UK says your combined hours should not average more than 48. If they do, you can sign an opt-out or reduce hours.

You can choose to work more than 48 hours a week on average if you are over 18. GOV.UK calls this opting out.

Key points from GOV.UK:

• Your employer can ask you to opt out, but you cannot be sacked or treated unfairly for refusing.
• You can opt out for a certain period or indefinitely.
• It must be voluntary and in writing.
• Your employer must keep a record that you have opted out.

GOV.UK publishes a short example agreement covering the average of 48 hours and the notice you will give (up to 3 months) if you change your mind. You can cancel an opt-out whenever you want, even if it is part of your contract. You must give at least 7 days' notice, or up to 3 months' if that is what your agreement says. Your employer cannot force you to cancel.

Some workers cannot use this opt-out route. GOV.UK lists groups including airline staff, workers on ships or boats, many road transport workers, and certain other staff covered by drivers' hours rules. Check GOV.UK and Acas if your sector may be different.

If you are under 18, GOV.UK says you cannot work more than 8 hours a day or 40 hours a week. Your hours cannot be averaged out in the adult 48-hour way: you cannot work more than 40 hours in any one week.

Those young worker limits sit alongside other young worker rules (including night restrictions). Do not treat an adult 48-hour opt-out form as a way around the under-18 daily and weekly caps. If a manager hands you adult paperwork, get advice before you sign.

Acas says employers must keep records to prove workers are not over the 48-hour weekly maximum (unless they have an opt-out), that night limits are respected, that night-worker health assessments have been offered, and that young workers are not working in a restricted period. Keep those records for 2 years. Keep your own diary, rota screenshots and messages as well.

The 48-hour rules are about health and safety limits on working time. Separately, the National Minimum Wage and National Living Wage ask whether you were paid enough for the hours that count for minimum wage purposes.

From April 2026, the National Living Wage for workers aged 21 and over is £12.71 an hour (always re-check the live GOV.UK rates table). If unpaid overtime you were asked to do, unpaid handover minutes, or unpaid "stay late" work counts for NMW purposes, it can pull your average hourly rate under the legal floor even when the headline rate looks legal.

Worked example in GBP

You are 30. Your contract rate is £12.71 an hour. In one pay week you are paid for 40 hours, but your manager also requires 5 hours of unpaid overtime that GOV.UK would treat as working time you were asked to do.

• Paid: 40 x £12.71 = £508.40
• Hours that should count if those 5 hours are working time for NMW: 45
• Effective rate: £508.40 ÷ 45 = £11.30 an hour

That sits under the April 2026 NLW of £12.71. Legal pay for 45 hours would be 45 x £12.71 = £571.95, so the gross gap is £63.55 for that week alone.

Acas says that if your employer is not following working time law, try informal talks or a grievance first. Depending on the issue, you may then make an employment tribunal claim, or report the matter to the Health and Safety Executive (HSE) or your local authority.

Acas is specific about the split. You can report to HSE or the local authority (depending on the workplace) problems such as the 48-hour maximum weekly working time limit, night work limits, health assessments for night work, and certain record-keeping requirements. Tribunal claims are the usual Acas route for rest breaks, daily rest, weekly rest and holiday entitlement, and for detriment if you raised a working time concern.

Unpaid wages and NMW underpayment are pay claims: raise them with the employer, then typically Acas Early Conciliation and tribunal, or (for NMW) an HMRC complaint. Acas says you generally choose either HMRC or tribunal for the same NMW underpayment. HSE's working time FAQ confirms it enforces the maximum weekly working time limit, night work limits and night-work health assessments, and does not enforce time off, rest breaks or paid annual leave. Hours breaches and pay shortfalls may need different tracks.

When the money is unpaid or under the minimum wage, watch the Acas employment tribunal time limits page (updated 4 September 2026):

• For most pay and wages claims today: 3 months minus 1 day from the date you were not paid correctly.
• From 1 October 2026: most claims become 6 months minus 1 day, but only if your time limit starts on or after 1 October 2026.
• Notifying Acas for Early Conciliation in time can pause the clock while conciliation runs.
• A grievance does not pause or extend the tribunal time limit.

• Treating "everyone opts out" as automatic. Opt-out must be individual, voluntary and in writing. Refusal must not cost you your job or fair treatment.
• Confusing a busy week with a breach. The adult limit is normally an average over 17 weeks (or another agreed reference period), not a ban on every week above 48.
• Signing an opt-out because unpaid overtime already exists. An opt-out does not legalise underpayment. NMW still applies to hours that count for minimum wage purposes.
• Assuming under-18s can use the adult opt-out to work 50-hour weeks. Young worker daily and weekly caps are different and stricter.
• Reporting only to HSE when the real loss is unpaid wages. Hours enforcement and pay claims can travel different routes.

If your weeks are ballooning and the payslip is not, start with a clean hours log. Paye Mes Heures can help you estimate unpaid time against rates and gather a clearer dossier (rotas, overtime asked for, opt-out paperwork, running shortfall) before you email your employer or contact Acas. It is a preparation aid, not a substitute for Acas, HSE, legal advice or a tribunal. Cross-check GOV.UK and Acas alongside it.

Protect your health and your pay. Count the average, check whether any opt-out is real, and treat unpaid hours as wages until proven otherwise.

• GOV.UK - Maximum weekly working hours: https://www.gov.uk/maximum-weekly-working-hours
• GOV.UK - Opting out of the 48 hour week: https://www.gov.uk/maximum-weekly-working-hours/weekly-maximum-working-hours-and-opting-out
• GOV.UK - Calculating your working hours: https://www.gov.uk/maximum-weekly-working-hours/calculating-your-working-hours
• Acas - Working time and rest / Working time rules: https://www.acas.org.uk/working-hours and https://www.acas.org.uk/working-time-rules
• Working Time Regulations 1998, regulation 4: https://www.legislation.gov.uk/uksi/1998/1833/regulation/4
• HSE - Working Time Regulations FAQ: https://www.hse.gov.uk/contact/faqs/workingtimedirective.htm
• GOV.UK - National Minimum Wage and National Living Wage rates: https://www.gov.uk/national-minimum-wage-rates
• Acas - Employment tribunal time limits: https://www.acas.org.uk/employment-tribunal-time-limits