Most UK employees are entitled to 5.6 weeks of paid holiday a year, but the exact number of days someone gets depends on how many days a week they work, when they joined, and whether their hours are fixed or irregular. This guide walks through the maths for each situation, including the 12.07% method used for casual and irregular hours staff.
In short:
- Full-time employees working a standard five day week get a statutory minimum of 5.6 weeks, which works out at 28 days a year.
- Part-time staff with fixed days or hours get the same entitlement, just worked out in proportion to how much they work.
- New starters get a pro-rated entitlement based on how much of the holiday year is left when they join.
- Casual or irregular hours workers usually build up holiday using the 12.07% method, based on the hours they actually work.
- Employers can set their own rules on whether unused holiday carries over or expires.
What is the legal minimum holiday entitlement in the UK?
Under the Working Time Regulations 1998, almost all workers in the UK are entitled to at least 5.6 weeks of paid holiday a year. For someone working a standard five day week, that comes to 28 days.
This statutory minimum can include the 8 UK bank holidays, or an employer can offer bank holidays on top of it. There is no automatic legal right to take bank holidays off on full pay separately from your main entitlement, it depends on what your contract says.
Many employers offer more than the legal minimum as part of their benefits package, so it is always worth checking a contract or staff handbook for the actual number offered.
How do you pro-rate holiday for part-time staff?
If someone works fewer days or hours than a full-time employee, but their working pattern is fixed and regular, their holiday entitlement is worked out proportionally. The formula is straightforward:
(Part-time days per week ÷ full-time days per week) × full-time entitlement
For example, if a full-time employee gets 28 days and a part-time colleague works 3 days a week instead of 5, their entitlement would be:
3 ÷ 5 × 28 = 16.8 days
The same logic applies if entitlement is measured in hours rather than days. This method is for staff with a fixed, regular working pattern. Casual or irregular hours workers are usually calculated differently, using the 12.07% method covered further down.
How do you calculate holiday for a new starter partway through the year?
When someone joins partway through your organisation’s leave year, their entitlement for that first year is pro-rated based on how much of the year is left from their start date.
A simple way to work this out is:
(Days remaining in the leave year ÷ total days in the leave year) × annual entitlement
For example, if your leave year runs from January to December and someone joins on 1 July with a full-time entitlement of 28 days, roughly half the year remains, so their entitlement for that first year would be around 14 days.
The exact figure will depend on the precise start date and how your organisation counts the year, and calculations often produce a fraction of a day. Many employers round this up to the nearest half or whole day as a matter of good practice, even though rounding down is technically permitted, since it tends to avoid confusion and disputes later on.
What is the 12.07% method and when does it apply?
The 12.07% method is a way of working out holiday entitlement for people who do not have fixed hours, such as casual staff, zero hours workers, and other irregular hours or part-year workers. It is not generally used for part-time employees who work a fixed, regular pattern each week, who are usually pro-rated using the simple formula above instead.
The 12.07% figure comes from dividing the statutory 5.6 weeks of holiday by the 46.4 weeks left in the year once that holiday is taken out (52 weeks minus 5.6 weeks). That gives 12.07% of hours worked.
For example, if someone works 20 hours in a month, their holiday for that period would be:
20 × 12.07% = 2.4 hours
Following changes to UK holiday pay rules that took effect for leave years starting on or after 1 April 2024, employers now have two accepted ways of paying irregular hours and part-year workers for their holiday: accruing it using the 12.07% method and paying it when leave is taken, or using rolled-up holiday pay, where the 12.07% uplift is added to normal pay and shown separately on the payslip. Because this is an area where the rules have changed recently, it is worth checking the current guidance on GOV.UK or ACAS before setting or changing a policy.
Should holiday carry over or expire?
Beyond the legal minimum, employers can set their own rules for what happens to unused holiday at the end of a leave year. Common approaches include:
- Allowing a set number of days to carry over into the next year
- Setting an expiry date by which carried over days must be used
- Not allowing any carryover at all, beyond the statutory minimum required by law in specific circumstances such as long term sickness or family leave
Whatever the policy, it helps to put it in writing and apply it consistently, so employees know exactly where they stand and managers are not left making judgement calls case by case.
Tips for getting holiday calculations right
- Review entitlements at the start of each leave year, not just when someone joins or leaves.
- Keep a clear, written policy on pro-rata, new starters, and carryover so everyone applies the same rules.
- Double check calculations for anyone who changes their working pattern partway through the year, for example moving from full-time to part-time.
- Use HR software to track balances automatically rather than relying on spreadsheets, especially once you have a mix of full-time, part-time, and casual staff.
- Communicate entitlement clearly to employees so there are no surprises when they come to book leave.
Calculating holiday entitlement, without the spreadsheet
Working out pro-rata days, new starter entitlements, and 12.07% accrual by hand is manageable for a handful of people, but it gets error-prone fast as a team grows or working patterns change. Sense HR’s holiday and leave tools calculate and track holiday entitlement automatically, including part-time, new starter, and irregular hours calculations, so balances stay accurate without manual maths.