Guide
Working Time limits that decide a shift pattern
Updated
Four published limits decide whether a pattern is lawful, and only one of them is the famous one. A rota that clears 48 hours a week and fails the daily rest rule is just as unlawful as one that does not, and it is far more common because nobody checks it.
Talk to a specialist Three numbers in, and you have the cycle, the average week, the crews and the Working Time position.
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How this calculator works
- The 48 hour average weekly limit is applied as gov.uk states it: "you cannot work more than 48 hours a week on average, normally averaged over 17 weeks". A worker may choose to opt out of the 48 hour week in writing, and several categories of work sit outside the limit entirely, including jobs requiring 24 hour staffing, the armed forces and emergency services, and roles where working time is not measured and the worker controls their own decisions (gov.uk).
- Average weekly hours are computed from the SHAPE of the cycle rather than from a calendar: days on divided by cycle length, times seven, times the shift length. That is exact for a repeating cycle and is why a 4 on 4 off 12 hour pattern produces 42 hours a week rather than the 48 people assume from the shift length.
- Daily rest is 11 hours between working days and the weekly rest is either an uninterrupted 24 hours each week or an uninterrupted 48 hours each fortnight. Workers also have the right to one uninterrupted 20 minute rest break during the working day where they work more than 6 hours (gov.uk).
- The daily rest figure assumes shifts on consecutive days start at the same clock time, so the gap is 24 hours minus the shift. A pattern that rotates forward from nights to days inside a cycle can produce a shorter gap than this figure shows, and that transition is the one to check by hand.
- Night workers are staff who regularly work at least 3 hours during the night period, which is 11pm to 6am unless the worker and employer agree a different period. They "must not work more than an average of 8 hours in a 24-hour period", usually calculated over 17 weeks, or up to 52 weeks by agreement. Where the work involves special hazards or heavy physical or mental strain the limit is absolute: they "cannot work longer than 8 hours in any 24-hour period" (gov.uk).
- The crew count is arithmetic, not a rota: shifts needed a day multiplied by the cycle length over the days on. It tells you how many crews the pattern implies for the cover you asked for. It does not account for holiday, sickness, training or the relief factor, all of which push the real headcount above it.
- Under 18s are not modelled. gov.uk states that under 18s "cannot work more than 8 hours a day or 40 hours a week", that 16 and 17 year olds "cannot work between midnight and 4am", and that they usually cannot work between 10pm and 6am, with narrow industry exceptions. Any pattern involving young workers needs checking against those rules directly.
- No figure here is a market rate, a typical pay rate or a benchmark. Everything the tool returns is derived from the pattern you enter and the published statutory limits, and nothing is estimated.
The 48 hour average week
gov.uk: "you cannot work more than 48 hours a week on average, normally averaged over 17 weeks". It is an average over a reference period, not a weekly ceiling.
A worker can opt out in writing. Whole categories sit outside it, including jobs requiring 24 hour staffing, armed forces, emergency services and police, security and surveillance, domestic service in a private household, seafarers and inland waterway workers, and roles where working time is not measured and the worker controls their own decisions.
Daily rest: 11 hours
gov.uk: "workers have the right to 11 hours rest between working days". On consecutive days at the same start time, the gap is 24 hours minus the shift, so a 12 hour shift leaves 12 hours and clears it, and a 14 hour shift leaves 10 and does not.
The pattern that breaks this quietly is the forward rotation: finishing a late shift and starting an early one the next morning. The rota shows two normal shifts and the gap between them can be under 11 hours. This is the limit most often breached by an otherwise compliant pattern.
Weekly rest
Either an uninterrupted 24 hours without any work each week, or an uninterrupted 48 hours without any work each fortnight. Both are stated on gov.uk and either satisfies the requirement.
The fortnightly alternative is what makes long consecutive runs workable. A 7 on 7 off pattern gives no 24 hour rest in the working week, and satisfies the rule through the 48 hours in the following fortnight instead.
Night work, and the version that does not average
Staff who regularly work at least 3 hours during the night period, 11pm to 6am unless a different period is agreed, are night workers. They must not work more than an average of 8 hours in a 24 hour period, usually calculated over 17 weeks, or up to 52 weeks by agreement.
The exception is the one to watch. Where the work involves special hazards or heavy physical or mental strain, gov.uk states they "cannot work longer than 8 hours in any 24-hour period". No averaging, no reference period. A 12 hour night shift on that kind of work is four hours over on every single occurrence, and a pattern averaging a comfortable 42 hours a week does not help at all.
The daily 20 minute break sits alongside all of this: an uninterrupted 20 minutes during the working day where the worker works more than 6 hours.