Pro Rata Annual Leave Calculator

How pro rata annual leave works in the UK

In the UK, all workers are legally entitled to 5.6 weeks of paid annual leave per year under the Working Time Regulations 1998. For a full-time employee working 5 days a week, that equates to 28 days (including bank holidays).

When an employee works fewer than 5 days a week, or joins part-way through a leave year, their entitlement must be calculated pro rata — meaning in proportion to the amount they work compared to a full-time equivalent.

The pro rata formula

For employees with a fixed weekly work pattern, the calculation is straightforward:

For example, an employee working 3 days a week with a full-time allowance of 28 days would receive: (3 ÷ 5) × 28 = 16.8 days.

Mid-year starters

When an employee starts part-way through the leave year, you need to further pro-rate their entitlement based on the portion of the year remaining:

For example, a part-time employee (3 days/week) who starts on 1 July with a Jan–Dec leave year would receive: 16.8 × (184 ÷ 365) = approximately 8.5 days.

Statutory minimum entitlement

The UK statutory minimum is 5.6 weeks of paid leave per year, capped at a maximum of 28 days. For part-time workers, the statutory minimum is:

The cap at 28 days means that employees working 6 or 7 days a week still receive a maximum of 28 days' statutory leave, even though 6 × 5.6 = 33.6.

Our calculator checks whether your company's allowance meets the statutory minimum. If you offer more than the statutory entitlement (which many employers do), the higher amount applies.

Bank holidays and pro rata leave

A common misconception is that bank holidays are separate from annual leave. In UK law, the 28-day statutory minimum includes bank holidays. Employers can choose to:

• Include bank holidays in the 28-day entitlement — meaning employees get 20 days to choose + 8 fixed bank holidays.
• Offer bank holidays on top of a base allowance — e.g. 25 days + 8 bank holidays = 33 days total. This is above the statutory minimum.

Part-time workers are entitled to bank holidays pro rata, even if the bank holiday doesn't fall on one of their normal working days. They can take the time off on an alternative day or have it added to their leave balance.

Irregular hours and zero-hours contracts

For workers without a fixed weekly pattern (such as zero-hours contracts or casual workers), calculating pro rata leave in “days” isn't practical. Instead, use the 12.07% accrual method:

From 1 January 2024, the Employment Rights (Amendment, Revocation and Transitional Provision) Regulations 2023 introduced a new accrual method for irregular hours and part-year workers, formalising the 12.07% approach.

Rounding pro rata leave

There is no legal requirement to round leave entitlement up or down. However, employers should be aware that:

• Rounding down risks non-compliance — if rounding down takes the entitlement below the statutory minimum, this is unlawful.
• Rounding up is safest — many employers round up to the nearest half or whole day to keep things simple and stay clearly above the minimum.
• Use exact figures where possible — leave management software can track fractional days, removing the need to round at all.

Common mistakes employers make

1. Using the wrong base figure — if your company offers 33 days (25 + 8 bank holidays) for full-time staff, you must pro-rate from 33, not 28.
2. Forgetting mid-year starters — new joiners part-way through the leave year need their entitlement adjusted for the remaining period.
3. Treating bank holidays separately for part-timers — part-time staff must receive bank holidays pro rata, even if their working days don't fall on bank holidays.
4. Using days when hours vary — if an employee works different hours on different days, calculating in hours is more accurate and fairer.
5. Not recalculating when patterns change — if an employee moves from 3 to 4 days per week mid-year, their leave balance needs adjusting.

Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000

Under these regulations, part-time workers have the right not to be treated less favourably than comparable full-time workers. This extends to annual leave: a part-time worker must receive the same proportion of leave as a full-time colleague. If full-time staff receive more than the statutory minimum, part-time staff must receive the same rate pro rata.

Let Leavely handle pro rata calculations

Manually calculating pro rata leave is error-prone, especially when you have employees with different work patterns, mid-year starters, and varying allowances. Leavely automates the entire process:

• Automatic pro rata entitlement based on each employee's work pattern
• Mid-year starter adjustments calculated from the actual start date
• Bank holiday pro-rating handled correctly for all work patterns
• Real-time balance tracking that updates as leave is booked, approved, or cancelled
• Statutory compliance checks to ensure every employee meets the legal minimum