How to Calculate Pro Rata Annual Leave UK: Formulas & Examples

Calculating annual leave for part-time employees is one of the most common HR headaches for UK small businesses. Get it wrong and you could be underpaying entitlement (illegal) or overpaying (costly). This guide gives you the exact formulas with worked examples.

The basic formula

For employees who work a fixed number of days per week, the calculation is simple:

The 5.6 comes from the statutory 5.6 weeks of leave that all UK workers are entitled to.

Quick reference table

Worked examples

Example 1: Employee works 3 days per week

Example 2: Employee works 4 days but different hours each day

When employees work different hours on different days, calculating in hours is more accurate than days.

Example 3: Employee starts mid-year (1 July)

Calculating for irregular hours workers

For workers with no fixed weekly hours (zero-hours contracts, casual workers), use the 12.07% method:

The 12.07% comes from: 5.6 weeks ÷ 46.4 working weeks (52 minus 5.6). For example, if a worker does 100 hours in a month, they accrue 12.07 hours of paid holiday.

Common mistakes

1. Rounding down — always round up or use exact figures. Rounding down risks underpaying statutory entitlement.
2. Forgetting bank holidays — part-time workers are entitled to bank holidays pro rata, even if they don't fall on their working days.
3. Using the wrong base — if your company offers more than statutory (e.g., 33 days for full-time), pro rata the company amount, not just 28.
4. Not adjusting for mid-year starters — new employees joining mid-year need their entitlement pro-rated for the remaining leave year.
5. Calculating in days when hours vary — if an employee works different hours on different days, use hours instead of days for accuracy.

Let Leavely handle the maths

Leavelycalculates pro rata entitlement automatically based on each employee's work pattern. Set the pattern once, and balances are always accurate — including for mid-year starters and bank holidays.