A week off raises your average
This is the thing every other working time calculator gets wrong, and it is worth understanding before anything else on this page.
Everybody assumes annual leave pulls the average down. A week at zero hours obviously drags a mean towards zero, so a fortnight away ought to buy you some headroom.
It does not work like that. Regulation 4(7) excludes days of annual leave, sick leave and maternity, paternity, adoption or parental leave from the reference period. They do not go in as zeros. The formula then makes them up with hours worked in the days immediately after the period, until the number of worked days matches the number excluded.
So the week off comes out, and a working week comes in behind it. Somebody sitting just under 48 before their holiday can be over it afterwards without having worked a single extra hour.
The tool shows both figures whenever they differ: what a spreadsheet would tell you, and what the regulations actually produce. The gap between them is the entire point.
The formula, since it is short
Regulation 4(3) is (A + B) ÷ C:
- A: hours worked during the reference period
- B: hours worked in the days after it, replacing the excluded days
- C: the number of weeks in the period
Note that C is the weeks in the period, not the weeks you happened to work. A blank week is a week that was worked with nothing recorded, which is why the tool asks you to put leave in the leave column rather than leaving a row empty.
48 is an average, not a cap
A single 60 hour week breaks nothing on its own. What matters is the average across the reference period, which is normally 17 weeks and normally rolling rather than sitting in fixed blocks.
Rolling has a consequence people miss: every week is a new average and a new answer.A calculation that came out fine today does not stay fine, because next week the oldest week drops off the back and a new one joins the front. One spreadsheet total signs nothing off for long.
Other periods exist. 26 weeks covers some special cases including doctors in training. Up to 52 is available where a collective or workforce agreement provides for it, for objective, technical or organisational reasons such as seasonal work, and offshore is 52. That is an agreement, not a decision an employer can take alone.
The opt-out, and the two things it is not
A worker can agree to work more than 48 hours on average. That agreement has to be in writing and separate from the employment contract, and it is voluntary: an employer must not cause somebody detriment for refusing to sign one. "You have to sign this to get the job" is not how it works.
Two things it does not do.
It is not permanent. A worker can cancel at any time on notice. That is seven days by law where the agreement is silent, and it can never be more than three months where it is not.
It does not touch rest. The opt-out applies to the 48 hour average and nothing else. Eleven hours between shifts, twenty four hours a week uninterrupted, and the twenty minute break all stand regardless of what has been signed. There is a separate checker for those, and they are the rules that get broken far more often.
Under 18: no averaging, no opt-out
A young worker is not on a smaller version of this regime. They are on a different one.
40 hours a week and 8 hours a day are hard limits, applied week by week. There is no reference period and no averaging, so a quiet week does not buy a busy one, and one 44 hour week is a breach even if the seventeen-week average is 25.
And none of it can be opted out of, by them or by their employer. Switch the tool to under 18 and it stops averaging entirely rather than lowering a threshold, because averaging is the thing that does not apply.
Drivers hours are a separate regime, not a variation
Some sectors have their own regimes that displace these rules, most obviously road transport, where drivers' hours and the road transport working time rules are a separate system with separate limits, and offshore work, which has its own reference period.
There are also exceptions for certain kinds of work and for workers whose working time is not measured or predetermined. This reports the default position, which is the right starting point rather than the last word.
Common questions
Is 48 hours a week a legal maximum?
No. It is an average over a reference period, normally 17 rolling weeks. A single 60 hour week breaks nothing on its own, and a tool that flags one is answering a question nobody asked. What matters is the average across the whole period.
Does a week of annual leave bring my average down?
It raises it, which is the opposite of what almost everybody expects. Regulation 4(7) excludes leave and sickness days from the reference period rather than counting them as zero hours, and the formula replaces them with hours worked in the days immediately after the period. So a fortnight away does not buy two low weeks of headroom: those weeks come out and two working weeks come in behind them.
Can my employer make me sign the opt-out?
No. It is a written agreement separate from your contract, it is voluntary, and an employer must not cause you detriment for refusing. It is also not permanent: you can cancel it at any time on notice, which is seven days by law if the agreement says nothing and can never be more than three months.
Does opting out affect my rest breaks?
No. The opt-out applies only to the 48 hour average: daily rest of eleven hours, weekly rest of twenty four, and the twenty minute break all stand regardless of what anybody has signed.
How long is the reference period?
Normally 17 weeks, and normally rolling rather than fixed blocks, so every week is a new average with a new answer. Some cases use 26 weeks, including doctors in training. Up to 52 is possible where a collective or workforce agreement provides for it, for objective, technical or organisational reasons such as seasonal work, and the offshore sector is 52.
Does this apply to under 18s?
No, and not because the numbers are smaller. A young worker is not averaged at all: 40 hours a week and 8 hours a day are hard limits applying week by week, so a quiet week does not buy a busy one. And there is no opt-out from any of it, by the worker or the employer.