Free Pro-Rata Calculator UK

How Pro-Rata Calculations Work in the UK

Pro-rata means "in proportion." In UK employment, pro-rata calculations are used whenever an employee works fewer hours or days than a full-time equivalent, or when they join or leave part-way through a leave year. Employers are legally required to give part-time staff a fair, proportional share of pay and holiday entitlement under the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000.

Pro-Rata Salary

To calculate a pro-rata salary, divide the actual hours worked per week by the full-time hours, then multiply by the full-time annual salary. For example, if a full-time role pays £30,000 for 37.5 hours per week and an employee works 22.5 hours, their pro-rata salary is £30,000 × (22.5 / 37.5) = £18,000 per year.

Pro-Rata Holiday Entitlement

Under the Working Time Regulations 1998, all workers in the UK are entitled to a minimum of 5.6 weeks of paid annual leave. For a full-time employee working five days a week, this equals 28 days. Part-time staff receive the same 5.6 weeks, but calculated proportionally. A worker doing three days per week receives 3 × 5.6 = 16.8 days of annual leave. For a detailed breakdown of how this works in practice, including bank holiday rules and irregular hours, see our part-time holiday entitlement guide.

Mid-Year Starters and Leavers

When an employee joins part-way through the leave year, their holiday entitlement must be pro-rated based on the remaining portion of the year. The formula is: full entitlement × (remaining calendar days / total days in year). For example, a worker starting on 1 July with a January-to-December leave year has 184 days remaining out of 365, so their entitlement would be 28 × (184 / 365) = 14.12 days. The same principle applies to leavers, where you calculate the proportion of the year already worked.

Rounding and the 28-Day Cap

Pro-rata calculations often produce fractional results. While there is no legal requirement to round up, employers must never round down below the statutory minimum. Most businesses round up to the nearest half or whole day for simplicity. It is also important to remember that statutory entitlement is capped at 28 days, regardless of how many days someone works per week. For more on statutory leave rules and common employer practices, see our UK holiday entitlement guide.

Why Accurate Pro-Rata Calculations Matter

Getting pro-rata figures right is not just good practice - it is a legal requirement. Underpaying part-time staff or short-changing their holiday entitlement can lead to tribunal claims under the Part-Time Workers Regulations. For small businesses managing a mixed team of full-time and part-time staff, having the right tools in place makes compliance straightforward and saves hours of manual calculation each year.