Payroll for part-time employees: pro-rata calculations

Part-time employees are entitled to the same pay and benefits as comparable full-time employees, on a pro-rata basis. The Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000 make it unlawful to treat a part-time worker less favourably than a comparable full-time worker doing similar work, unless there is an objective justification. Understanding how to calculate pro-rata pay and benefits correctly is essential for any employer with a mixed full-time and part-time workforce.

Pro-rata salary calculation is straightforward: divide the full-time equivalent salary by the full-time hours per week, then multiply by the part-time hours. A full-time role paying £30,000 for 37.5 hours per week translates to a part-time salary of £20,000 for a 25-hour week (25/37.5 × £30,000).

Holiday entitlement is also calculated pro-rata. The statutory minimum of 5.6 weeks applies, with the annual leave number reflecting the part-time hours. A 25-hour-per-week employee working five days per week on shorter days has a different calculation than a three-day-per-week employee. The safest approach is to express holiday entitlement in hours rather than days, to avoid ambiguity when shifts are not equal.

Pensionable pay under auto-enrolment is assessed on the part-time salary, not the FTE equivalent. A part-time employee earning £8,000 per year falls below the auto-enrolment earnings trigger (£10,000), so is not automatically enrolled — though they retain the right to opt in and receive employer contributions as a non-eligible jobholder.

Statutory payments — SSP, SMP, SPP — are all based on average weekly earnings from actual part-time pay, not FTE. For SSP, the employee must earn above the lower earnings limit on their actual part-time pay to qualify. A part-time employee earning very low hours may not reach the lower earnings limit.

Bonus and commission schemes need careful attention. A part-time employee is entitled to be considered for bonus on the same basis as a comparable full-time employee, unless the scheme is genuinely time-related in a way that objectively justifies a pro-rata approach. A blanket policy of not paying bonus to part-time staff is unlawful.

Holiday pay for part-time workers must be calculated on actual pay earned, not FTE. Where a part-time worker receives irregular earnings — such as shift premiums or overtime — the 52-week rolling average applies to determine holiday pay rate, as it does for irregular-hours workers generally. See our guide on holiday pay calculations after the Harpur Trust ruling.

Salary sacrifice works for part-time employees subject to the same rules as full-time — the sacrifice cannot reduce pay below minimum wage, and the effect on statutory payments must be considered.

See PAYE explained for how tax and NI are calculated on part-time pay, and running your first payroll for setting up part-time employees in payroll for the first time.

Mellow handles pro-rata calculations for holiday, pension, and statutory pay across a mixed full-time and part-time workforce. [Start a free trial →](https://mellowhr.com/register)