Shift worker holiday calculator

Why "days" is the wrong unit for shift work

The statutory minimum is defined in weeks: 4 weeks under Working Time Regulations 1998, reg 13, plus a further 1.6 weeks under reg 13A — 5.6 weeks combined. The familiar "28 days" figure that gov.uk quotes is just that 5.6 weeks multiplied by a 5-day week: 5.6 × 5 = 28. It is a convenience, not a separate right, and it only works cleanly because it also assumes every one of those 5 days is the same length as every other day the person works.

A shift worker breaks that assumption twice over. First, a rota like 4-on/4-off doesn't average 5 working days a week at all. Second, and more easily missed, each working day might be 12 hours rather than whatever generic length a payroll system was built around. "One day of leave" carries no information about how many hours it is worth — and when that missing information defaults to the wrong number, the error is invisible, because the sum still looks tidy in "days" on both sides.

The three ways employers count it

In practice, employers land on one of three units. Each is correct on its own terms; the difference is what happens when your working pattern isn't a plain 5-day week of identical days.

Counting in days

This is 5.6 weeks pro-rated by how many days a week you work on average, then treated as a bank of "days" to book off. For someone averaging 3.5 days a week rather than 5, that's 28 × (3.5 ÷ 5) = 19.6 days. The pro-ration itself is sound — the problem is what comes next. Nineteen-point-six days is only the right answer if everyone agrees what one of those days is worth in hours. If your shift is 12 hours and the number "19.6 days" gets fed into a system that assumes a generic 7.5-hour day, you and your employer are now using the same word to mean two different amounts of leave.

Counting in weeks

The 5.6-week figure is the one guaranteed to be right, because it's what regs 13 and 13A actually say, and it doesn't need converting for anyone's pattern. Its limitation is practical rather than legal: nobody books "0.4 of a week" off a rota. Weeks are the figure to check your total against, not the figure to hand to a scheduler.

Counting in hours

Multiply 5.6 weeks by your average weekly hours and you get entitlement in hours — a figure with no ambiguity left in it, because "an hour" means the same thing on every rota. Divide that hours total by your actual shift length and you get exactly how many shifts you can book off, whatever your pattern is now and whatever it changes to later. This is the method that actually works for shift workers: the other two units quietly stop meaning what they say once the working pattern stops being a plain 5-day week, and hours don't.

Which method applies to you

If you work a fixed, repeating pattern where every shift is the same length — 4-on/4-off at 12 hours is the example used throughout this page — hours is the safest unit, and days will only match it if your contract explicitly defines a "day" as one shift, not a generic office day. If your shift length itself varies from one shift to the next, hours is really the only option that won't misstate your entitlement, because there's no single day-length left to pro-rate against.

There's one more boundary worth knowing. If your paid hours are, under your contract, "wholly or mostly variable" from one pay period to the next, you may instead be an irregular hours worker under reg 15F(1)(a) of the Working Time Regulations — a different calculation covered on our irregular hours calculator. A fixed, predictable rota such as 4-on/4-off generally does not meet that test, so the methods on this page — not the 12.07% rolled-up-pay regime — are what apply to you.

What a day's holiday is actually worth in pay

Most explanations stop at how many days or hours you get. Fewer cover what each hour of that leave should be paid at — and for shift workers, that's the part most likely to be wrong. The rules sit in Employment Rights Act 1996, ss.221–224, as applied to holiday pay by Working Time Regulations 1998, reg 16 "with modifications" — the modification that matters most is the reference period.

Which ERA section governs your week's pay depends on how your pay is structured:

• s.221(2) — your pay is fixed regardless of the hours the rota puts in any given week (a salaried shift worker, for example).
• s.221(3) — you're paid by the hour and your total pay varies week to week purely because a rota like 4-on/4-off puts different numbers of hours into different calendar weeks.
• s.222 — your rate of pay itself changes depending on when you work. The section applies, in its own words, where remuneration "varies according to the incidence of those days or times" — precisely a night-shift or weekend premium sitting on top of a base rate.
• s.224 — you have no normal working hours at all. That's a different situation from a fixed rota with normal hours that simply falls differently across weeks, and it's the territory the irregular hours calculator covers.

A worked example: four on, four off

Priya works a 4-on/4-off rota, 12-hour shifts, alternating two day shifts at £14/hour and two night shifts at a £2/hour premium — £16/hour.

• Hours per 8-day cycle: 4 shifts × 12 hours = 48 hours.
• Average hours per week: 48 ÷ 8 × 7 = 42 hours. (Average days per week: 4 ÷ 8 × 7 = 3.5 days.)
• Entitlement in weeks: the statutory 5.6 weeks — unchanged by any of this.
• Entitlement in hours: 5.6 × 42 = 235.2 hours a year.
• Entitlement in her own shift-days: 235.2 ÷ 12 = 19.6 shifts. Cross-checked the other way — 28 days × (3.5 ÷ 5) = 19.6 days — the two routes agree, because both correctly use her 12-hour shift as "a day".
• Where it goes wrong: if that same 19.6-day figure were valued at a generic 7.5-hour day instead of her actual 12-hour shift, it would come to 19.6 × 7.5 = 147 hours — a shortfall of 235.2 − 147 = 88.2 hours, over seven of her 12-hour shifts, for no reason other than the wrong day-length being substituted in.
• Her average hourly rate (per block of 2 day + 2 night shifts): (2 × 12 × £14) + (2 × 12 × £16) = £336 + £384 = £720 over 48 hours = £15.00/hour.
• Her week's pay for holiday purposes (s.222 mechanics: average weekly hours × average hourly rate): 42 × £15.00 = £630.00.
• One 12-hour shift of holiday is worth 12 × £15.00 = £180.00.
• Her full annual entitlement is worth 5.6 × £630.00 = £3,528.00 — the same figure as 235.2 × £15.00 = £3,528.00, confirming the weeks route and the hours route agree.

When your rota changes

If your shift pattern changes for good — a different shift length, a different number of days a week — redo the conversion above from the new average weekly hours, and treat the changeover date as a split point: entitlement built up under the old pattern stays as it was, and entitlement from the changeover onward is calculated fresh under the new one.

Pay is slower to catch up than entitlement. Because the reference period is a rolling 52-week look-back under reg 16, your average hourly "week's pay" figure doesn't switch over on the day your rota changes — it blends old-pattern weeks and new-pattern weeks together until a full 52 weeks under the new pattern have rolled through the window. Expect the figure to keep moving for up to a year after a genuine change, not settle immediately.

One more check worth making when a rota changes: if the new pattern no longer repeats in any predictable way — hours genuinely different every pay period, rather than a fixed cycle like 4-on/4-off — you may have moved from a fixed shift pattern into irregular hours worker territory, which is calculated under a different regime entirely.