Every UK worker is entitled to 5.6 weeks of paid leave a year. To pro-rata, multiply 5.6 by their days per week (or in hours, by their weekly hours). For a mid-year joiner or leaver, take the annual entitlement and multiply it by the proportion of the leave year worked. For a change of hours mid-year, ACAS recommends recalculating from the change date. Always round up · never down. Three live calculators below cover all three scenarios.
The 5.6 weeks rule
Every pro-rata sum starts from the same figure: 5.6 weeks of paid leave a year, set by regulations 13 and 13A of the Working Time Regulations 1998. It is set in weeks so it scales with any working week. For a regular worker, multiply by their days per week.
The other scenarios each tweak that sum, and there is a calculator below for each: irregular daily hours (multiply 5.6 by weekly hours), a mid-year joiner or leaver (scale by the fraction of the year worked), and a change of hours mid-year (split the year and accrue under each pattern). For the theory behind the 5.6 multiplier, see our UK annual leave entitlement guide.
Calculator 1: pro-rata by working pattern
Use this calculator for a worker on a regular weekly pattern. Pick days or hours, enter the worker's pattern, and get their annual entitlement. The full-time allowance defaults to 28 days (the statutory minimum including bank holidays); change it if your business offers more.
The calculator does the standard pro-rata sum: full-time entitlement multiplied by the worker's pattern as a fraction of full-time, rounded up. For the four-day-week scenario specifically (the most common pro-rata question we get), see our 4-day-week holiday guide. For the broader part-time view, the part-time pro-rata guide covers wider ground.
Calculator 2: mid-year joiners and leavers
Workers who join or leave during the leave year get a pro-rata slice of the annual entitlement. This calculator uses the proportion-of-year method, which both GOV.UK and ACAS accept as the correct approach for regular-hours staff.
GOV.UK and ACAS allow either the proportion-of-year method (used above) or the 1/12-per-month accrual method. Both reach a similar answer for a regular-hours starter. The 1/12 method gives one full month's accrual for any complete or part month worked, which can produce a slightly more generous figure for a worker joining late in a month.
For more on the joiner side specifically, our new starters holiday entitlement guide walks through both methods step by step. For leavers, our unused annual leave on termination guide covers what's owed on the final payslip, including how to value any unused entitlement.
Calculator 3: change of hours mid-year
This is the trickiest scenario. A worker is on a regular pattern, then changes hours partway through the leave year · perhaps reducing from full-time to three days, or going the other way. ACAS guidance (calculating holiday pay) is clear: don't just switch them onto the new annual entitlement. You have to split the year and accrue separately under each pattern.
A common mistake is recalculating the worker's full-year entitlement at the new pattern, then deducting any leave already taken. That undercounts the time the worker spent on the old pattern. Always split the year and accrue separately · the calculator above does this for you.
Track in days if the worker does the same shift length every day. Track in hours if their daily hours vary, otherwise a 12-hour shift costs the same 'one day' as a 5-hour one, which is unfair and breaches the Part-Time Workers Regulations 2000. Irregular-hours and zero-hours staff are different again: they fall under the post-April 2024 12.07% accrual rules, covered in our irregular hours holiday pay guide.
Rounding rules
Round up. Never down. The Working Time Regulations 1998 set 5.6 weeks as a statutory floor, and the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000 prevent any pro-rata calculation that produces less favourable treatment. ACAS confirms in its checking holiday entitlement guidance that part-day or part-hour figures may be rounded up to the nearest half-day or whole hour.
| Calculation result | Round to | Rationale |
|---|---|---|
| 22.4 days | 22.5 days | Up to nearest half-day |
| 16.8 days | 17 days | Up to nearest whole day (or 17 if half-days not tracked) |
| 11.2 days | 11.5 days | Up to nearest half-day |
| 156.8 hours | 157 hours | Up to nearest whole hour |
| 4.8 days | 5 days | Up to nearest whole day |
The choice between half-days and whole days is yours · whatever your booking system supports. The rule is just that you cannot end up with less than the statutory floor or less than the contractual entitlement (whichever is higher).
Bank holiday pro-rata
If full-time staff get bank holidays as paid leave on top of their entitlement, part-timers must get a pro-rata bank holiday allowance to comply with the Part-Time Workers Regulations 2000. The default is England's eight bank holidays · so a 4-day-a-week worker gets 8 x 4/5 = 6.4 days, normally rounded up to 6.5.
Scotland has nine statutory bank holidays and Northern Ireland has ten, so adjust the pro-rata accordingly:
| Days/week | England (8 BH) | Scotland (9 BH) | NI (10 BH) |
|---|---|---|---|
| 5 days (full-time) | 8.0 | 9.0 | 10.0 |
| 4 days | 6.5 (6.4) | 7.5 (7.2) | 8.0 |
| 3 days | 5.0 (4.8) | 5.5 (5.4) | 6.0 |
| 2 days | 3.5 (3.2) | 4.0 (3.6) | 4.0 |
| 1 day | 2.0 (1.6) | 2.0 (1.8) | 2.0 |
(Pro-rata raw figures in brackets; rounded-up figures in front.) Where bank holidays are simply included within the 28-day annual allowance rather than granted on top, the calculator above already handles that · you don't need a separate bank holiday allowance.
The ACAS Pat example
The ACAS guidance on calculating holiday pay walks through a worked example for a worker called Pat who changes hours mid-year. It's the canonical case for change-of-hours scenarios, and it's worth understanding the structure:
Pat works full-time at 40 hours per week from 1 January to 31 March (3 months), then drops to 20 hours per week from 1 April to 31 December (9 months). Leave year runs 1 January to 31 December.
At 40 hours per week, statutory entitlement is 40 x 5.6 = 224 hours per year. Pat works 3 of 12 months at this rate, so accrues 224 x (3/12) = 56 hours.
At 20 hours per week, statutory entitlement is 20 x 5.6 = 112 hours per year. Pat works 9 of 12 months at this rate, so accrues 112 x (9/12) = 84 hours.
Pat's full-year entitlement is 56 + 84 = 140 hours. That's the figure the employer must give Pat across the leave year. Note this is more than 20 x 5.6 = 112 (the new pattern's annual entitlement) · because Pat earned the full-time accrual for those first three months.
Calculator 3 above does the same calculation in days. The principle is identical: split the year, accrue separately, sum the two parts.
Worked examples
Three common scenarios with the maths shown, handy if you're writing a policy or auditing existing allowances.
Sources and primary references
| 5.6 weeks rule | Working Time Regulations 1998 (regs 13 and 13A) |
| Pro-rata principle | Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000 |
| Calculate entitlement (official) | GOV.UK · Calculate your holiday entitlement |
| Holiday entitlement rights | GOV.UK · Holiday entitlement |
| Checking holiday entitlement | ACAS · Checking holiday entitlement |
| Calculating holiday pay (Pat example) | ACAS · Calculating holiday pay |
Frequently asked questions
How do I calculate pro-rata holiday entitlement in the UK?
Take 5.6 weeks (the statutory minimum) and multiply by the worker's days per week. So 5 days = 28 days, 4 days = 22.4 days, 3 days = 16.8 days, and so on. If hours vary day-to-day, multiply 5.6 by their weekly hours instead · this gives an entitlement in hours rather than days. Always round any half-day result up, never down. The Working Time Regulations 1998 and the Part-Time Workers Regulations 2000 both apply.
How is holiday pro-rated for someone joining mid-year?
GOV.UK and ACAS allow two methods. The proportion-of-year method takes the full annual entitlement and multiplies it by the fraction of the leave year remaining when the worker joins. The 1/12 monthly accrual method gives one-twelfth of the annual entitlement for each complete or part month worked. Both reach a similar answer for regular-hours staff. The result is rounded up to the nearest half day or day · never down.
What if a worker changes hours mid-year?
Where a worker on regular hours changes their working pattern during the leave year, ACAS recommends recalculating their entitlement on a pro-rata basis from the date of the change. Calculate what the worker has accrued at the old rate up to the change date, then add what they accrue at the new rate from the change date to the end of the leave year. The two figures combine to form their full year's entitlement under the new pattern.
Should pro-rata holiday be tracked in days or hours?
For workers with the same hours every working day, days work fine. For workers whose daily hours vary (a 12-hour shift followed by a 5-hour one), GOV.UK recommends tracking entitlement in hours: weekly hours times 5.6 gives annual entitlement in hours. This is essential for fairness · otherwise a worker booking off a 12-hour shift uses the same 'one day' of leave as someone booking off a 5-hour shift.
Do I round pro-rata holiday up or down?
Up only. The Working Time Regulations 1998 set 5.6 weeks as a floor, and the Part-Time Workers Regulations 2000 prevent less favourable treatment. ACAS confirms that part-day or part-hour entitlements may be rounded up to the nearest half-day or whole hour for ease of administration, but never rounded down. So 22.4 days becomes 22.5; 16.8 days becomes 17 (or 16.5 if half days are tracked); 11.2 hours becomes 11.5.
Do bank holidays need to be pro-rated for part-time workers?
If full-time staff get bank holidays as paid leave on top of their entitlement, part-timers must receive a pro-rata bank holiday allowance to comply with the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000. For the eight bank holidays in England, that is 8 multiplied by the part-timer's days per week then divided by 5. So a 4-day worker gets 6.4 days (rounded to 6.5); a 3-day worker gets 4.8 days (rounded to 5).
Does it matter which days a part-timer works for bank holidays?
Yes, which is why a pro-rata allowance is the fair fix. Most bank holidays fall on a Monday. If you only give a part-timer the bank holidays that land on their working days, a Monday worker does well and a Friday worker gets almost none. A pro-rata bank holiday allowance (8 x days per week / 5 in England) gives every part-timer the same share whatever days they work, as the Part-Time Workers Regulations 2000 require.
This guide is for general information and is not legal advice. For guidance on a specific situation, contact the Acas helpline on 0300 123 1100 or speak to an employment solicitor.