How to Calculate Holiday Entitlement for Part-Time Employees in the UK

Getting holiday entitlement wrong for part-time employees is one of the most common — and most expensive — mistakes UK employers make. Underpay, and you face tribunal claims and back-pay orders. Overpay consistently, and you quietly bleed money you never needed to spend.

The rules are more nuanced than most people realise, especially since the Supreme Court’s landmark ruling in Harpur Trust v Brazel changed the calculation method for irregular-hours workers. This guide walks you through every scenario: fixed part-time patterns, irregular hours, term-time workers, and zero-hours contracts — with worked examples you can apply immediately.

The Legal Foundation: What Part-Time Workers Are Entitled To

Under the Working Time Regulations 1998, every worker in the UK is entitled to 5.6 weeks of paid annual leave per year. For a full-time employee working five days a week, that translates to 28 days (5.6 × 5).

Part-time employees receive the same entitlement on a pro-rata basis. This is reinforced by the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000, which make it unlawful to treat part-time workers less favourably than comparable full-time colleagues.

The key principle: part-time workers get the same proportion of leave as full-time workers, adjusted for their working pattern.

The Pro-Rata Formula for Fixed-Pattern Part-Time Workers

If an employee works a consistent number of days each week, the calculation is straightforward.

The Formula

Annual holiday entitlement = Days worked per week × 5.6

Worked Examples

Example 1: Employee working 3 days per week

• 3 × 5.6 = 16.8 days annual leave per year
• You can round this up to 17 days (you must never round down)

Example 2: Employee working 2.5 days per week

• 2.5 × 5.6 = 14 days annual leave per year

Example 3: Employee working 4 days per week

• 4 × 5.6 = 22.4 days annual leave per year
• Round up to 23 days

When the Employee Works Hours, Not Days

Some part-time employees work patterns measured in hours rather than days — for instance, 20 hours per week instead of a set number of days.

Annual holiday entitlement in hours = Weekly hours × 5.6

Example: Employee working 20 hours per week

• 20 × 5.6 = 112 hours annual leave per year

Example: Employee working 15 hours per week

• 15 × 5.6 = 84 hours annual leave per year

This is important because a “day” of leave for someone who works 4-hour shifts is not the same as for someone who works 8-hour shifts. Calculating in hours ensures fairness.

Bank Holidays and Part-Time Workers

This is where many employers go wrong. There is no statutory right to take bank holidays off — the 5.6 weeks’ entitlement can include bank holidays.

The Problem with “Plus Bank Holidays”

If your full-time employees receive “28 days plus 8 bank holidays” (effectively 36 days total), you must give part-time workers a pro-rata equivalent of the total package. Simply giving a part-time worker their 5.6 weeks and then saying “bank holidays don’t apply to you” would be less favourable treatment.

How to Calculate Bank Holiday Entitlement for Part-Timers

Step 1: Work out the full-time total entitlement (e.g., 28 days + 8 bank holidays = 36 days)

Step 2: Pro-rata the entire amount

Example: An employee working 3 days per week where full-timers get 28 + 8 = 36 days

• (3 ÷ 5) × 36 = 21.6 days total annual leave (round up to 22)
• This includes their bank holiday entitlement

The Fairness Issue with Specific Days

A part-time employee who works Mondays and Tuesdays will “lose” more bank holidays than someone who works Thursdays and Fridays, since most UK bank holidays fall on Mondays. To handle this fairly:

1. Option A: Include bank holidays in the total entitlement and let part-timers choose when to use their leave
2. Option B: Give all employees the bank holidays off and adjust remaining leave accordingly
3. Option C: Require everyone to work bank holidays (rare outside certain sectors) and allocate the full pro-rata entitlement as bookable leave

Option A is the most common and cleanest approach. It avoids the complexity of tracking which bank holidays fall on which employee’s working days.

The 12.07% Accrual Method for Irregular-Hours Workers

For workers without fixed weekly hours — agency workers, zero-hours contract workers, casual staff — the traditional pro-rata formula does not work because there is no consistent weekly pattern to base it on.

Where 12.07% Comes From

The figure 12.07% is derived from the proportion of the year that statutory leave represents:

• 5.6 weeks’ leave ÷ (52 weeks - 5.6 weeks) = 5.6 ÷ 46.4 = 0.1207 or 12.07%

The denominator is 46.4 because that is the number of weeks actually worked in a year (52 minus 5.6 weeks of holiday).

How to Apply It

For each pay period, calculate:

Holiday accrual = Hours worked in the period × 12.07%

Example: A zero-hours worker does 30 hours in a week

• 30 × 12.07% = 3.62 hours of holiday accrued that week

Example: Over a month, a casual worker does 80 hours

• 80 × 12.07% = 9.66 hours of holiday accrued that month

Rolled-Up Holiday Pay

Since April 2024, rolled-up holiday pay is once again lawful for irregular-hours and part-year workers under the Employment Rights (Amendment, Revocation and Transitional Provision) Regulations 2023. This means you can add the 12.07% directly onto each payment rather than accruing leave to be taken later.

If you use rolled-up holiday pay, it must be shown as a separate line item on the payslip so the worker can see exactly what they are receiving.

The Harpur Trust v Brazel Ruling: What Changed

The Supreme Court’s 2022 decision in Harpur Trust v Brazel [2022] UKSC 21 fundamentally changed how holiday entitlement is calculated for part-year workers — those who work for only part of the year, such as term-time-only staff.

The Old Approach

Before this ruling, many employers used the 12.07% method for part-year workers, calculating holiday based on hours actually worked. This seemed logical: if someone only works 32 weeks a year, their holiday should reflect that.

What the Supreme Court Said

The Court ruled that the 12.07% method should not be used for part-year workers with permanent contracts. Instead, these workers are entitled to 5.6 weeks of leave, with each week’s pay calculated based on their average weekly earnings over a 52-week reference period (ignoring weeks with no pay).

The Practical Impact

Example: A term-time music teacher working 32 weeks per year, earning £200 per week when working

Old method (12.07%):

• Total hours worked: 32 weeks × 30 hours = 960 hours
• Holiday accrual: 960 × 12.07% = 115.87 hours ≈ 3.86 weeks

Post-Brazel method:

• Entitlement: 5.6 weeks
• Weekly pay: Average over 52 weeks (ignoring nil weeks) = £200
• Total holiday pay: 5.6 × £200 = £1,120

The worker receives 5.6 weeks regardless of how many weeks they actually work. This can mean part-year workers receive proportionally more holiday than full-year workers — and the Supreme Court confirmed this is the correct legal position.

Legislative Response

The government partially addressed this through the Employment Rights (Amendment, Revocation and Transitional Provision) Regulations 2023, which introduced a new category of “irregular hours workers” and “part-year workers” for leave years beginning on or after 1 April 2024. For these workers, an accrual method based on 12.07% of actual hours worked in each pay period is now permitted again.

However, this only applies to genuinely irregular-hours or part-year workers. If an employee has a fixed part-time pattern (even if they only work part of the year), you need to consider carefully which category they fall into.

Term-Time Workers: A Special Case

Term-time workers remain one of the trickiest categories. Here is how to handle them correctly post-2024:

If They Qualify as “Part-Year Workers” Under the 2023 Regulations

• Use the accrual method: 12.07% of hours worked per pay period
• Or use rolled-up holiday pay (adding 12.07% to each payment)

If They Do Not Qualify (e.g., Permanent Contract with Set Hours Each Term)

• Apply the Brazel ruling: 5.6 weeks’ entitlement
• Calculate weekly pay using the 52-week reference period (skipping nil weeks)
• Holiday should ideally be taken during non-working periods

Practical Tip

Schedule term-time workers’ annual leave during school holidays. This way, they receive their holiday pay during weeks they would not otherwise work, and it does not disrupt term-time operations.

Zero-Hours Contract Workers

Zero-hours workers almost always fall into the “irregular hours worker” category under the 2023 Regulations.

Recommended Approach

1. Accrual method: Track hours worked each pay period and accrue holiday at 12.07%
2. Rolled-up holiday pay: Add 12.07% to every payment (simpler to administer)
3. Record keeping: Maintain clear records of hours worked, holiday accrued, and holiday taken

Common Mistake

Do not assume zero-hours workers are not entitled to holiday. Every worker in the UK — regardless of contract type — is entitled to 5.6 weeks’ paid annual leave. HMRC and employment tribunals take a dim view of employers who fail to provide this.

Employees Who Change Their Working Pattern Mid-Year

When an employee changes from full-time to part-time (or vice versa) during the leave year, you need to recalculate their entitlement.

The Method

1. Calculate entitlement for the period at the old pattern
2. Calculate entitlement for the period at the new pattern
3. Deduct any leave already taken
4. The result is remaining entitlement for the rest of the year

Example: An employee works full-time (5 days/week) from January to June, then drops to 3 days/week from July to December. Leave year is January to December.

• Jan–Jun (26 weeks): (26 ÷ 52) × 28 = 14 days entitlement at full-time rate
• Jul–Dec (26 weeks): (26 ÷ 52) × 16.8 = 8.4 days entitlement at part-time rate
• Total: 22.4 days (round up to 23)
• Deduct any days already taken in Jan–Jun

Common Mistakes Employers Make

1. Rounding Down Instead of Up

If a calculation produces a fraction (e.g., 16.8 days), you must round up to 17. Rounding down means the employee receives less than their statutory entitlement, which is unlawful.

2. Excluding Bank Holidays for Part-Timers

If full-time staff receive bank holidays on top of their 28 days, part-time staff must receive a pro-rata share of the total package (including bank holidays).

3. Using the Wrong Method for Part-Year Workers

Since the 2023 Regulations, you must determine whether a worker is genuinely an “irregular hours” or “part-year” worker before applying the 12.07% accrual method. Get the categorisation wrong, and you may owe back pay.

4. Not Recalculating When Patterns Change

If an employee’s hours change, their holiday entitlement must be recalculated. Continuing to apply the old rate is a compliance risk.

5. Failing to Keep Records

HMRC expects employers to maintain records of holiday entitlement, accrual, and usage. Without clear records, you cannot defend yourself if a worker brings a claim.

6. Confusing Calendar Days with Working Days

An employee who works 3 days per week and takes a week of holiday uses 3 days of entitlement, not 5 or 7. Always count leave in the same unit as the employee’s working pattern.

How Leave Balance Makes Part-Time Holiday Calculations Simple

Manually calculating holiday entitlement for a workforce with mixed patterns — full-time, part-time, zero-hours, term-time — is an invitation for errors. One miscalculation can cascade into payroll mistakes, underpayments, and tribunal claims.

Leave Balance handles the complexity automatically:

• Custom leave policies per employee or group — set different accrual rates for full-time, part-time, and irregular workers without maintaining parallel spreadsheets
• Automatic pro-rata calculations — enter the working pattern once, and the system calculates entitlement correctly, including bank holiday adjustments
• Mid-year pattern changes — when an employee moves from full-time to part-time, Leave Balance recalculates remaining entitlement instantly
• Multi-country support — if you have employees across the UK and Europe with different statutory minimums, Leave Balance tracks them all in one place
• Slack and Microsoft Teams integration — employees can check their balance and request leave without logging into a separate system

At $10/month flat rate for unlimited employees and policies, there is no per-head cost that scales awkwardly as your team grows. And with a 14-day free trial (no credit card required), you can test it with your actual workforce data before committing.