Pro rata is Latin for "in proportion". In UK pay and employment it means scaling a full-time figure down to the share of full-time hours or of the year that someone actually works. A job advertised at £36,000 pro rata for 22.5 hours against a 37.5-hour full-time week pays 60% of £36,000, which is £21,600. Part-time workers are legally entitled to at least this proportion of full-time pay and benefits, and to 5.6 weeks of paid holiday scaled to their working week.
What "pro rata" means in a job advert
When a salary is quoted "pro rata", the figure shown is the full-time equivalent (FTE), not what the job will pay. To work out the actual salary, multiply the FTE by the fraction of full-time hours the role involves:
Actual salary = full-time salary × (your contracted hours ÷ full-time hours)
The same approach applies to a job that covers only part of the year. A role paying £30,000 pro rata that runs for six months pays £15,000 over that period. Where both hours and weeks are reduced, apply both fractions.
Worked examples
| Scenario | Calculation | Result |
|---|---|---|
| £36,000 FTE, 22.5 of 37.5 hours | £36,000 × 22.5 ÷ 37.5 | £21,600 a year |
| £36,000 FTE, 3 of 5 days | £36,000 × 3 ÷ 5 | £21,600 a year |
| £30,000 FTE, 6-month contract | £30,000 × 6 ÷ 12 | £15,000 |
| Hourly rate check, £36,000 FTE at 37.5 hours | £36,000 ÷ (37.5 × 52) | £18.46 an hour |
The hourly rate is a useful cross-check. A pro rata salary should give the same hourly rate as the full-time salary. If it does not, the arithmetic, or the employer's offer, needs another look.
The legal basis: the pro rata principle
The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 give part-time workers the right not to be treated less favourably than a comparable full-time worker, either in their contract terms or by any other detriment. The protection applies where the treatment is because the worker is part-time and is not objectively justified. When deciding whether treatment is less favourable, the "pro rata principle" applies unless it is inappropriate.
Regulation 1 defines that principle. Where a comparable full-time worker gets pay or any other benefit, the part-time worker must get at least the same proportion of it as their weekly hours bear to the full-time worker's weekly hours. Weekly hours are the contracted hours in a normal week, ignoring absences and overtime, or an average where hours follow a cycle. Because the definition covers "pay or any other benefit", it reaches beyond basic salary to contractual benefits such as bonuses and enhanced sick pay.
One exception is overtime rates. A part-time worker who is paid a lower overtime rate is not treated less favourably for that reason until their total hours, including overtime, exceed the full-time worker's normal hours.
Pro rata holiday
Holiday is the most common pro rata calculation in payroll. The statutory entitlement is 5.6 weeks a year, which is 28 days for someone working five days a week, and the statutory entitlement is capped at 28 days. A part-time worker with regular hours gets 5.6 times their working week. Someone who works three days a week is entitled to at least 16.8 days. Employers may count bank holidays as part of the statutory entitlement. When they do, check that part-time staff still receive their full pro rata entitlement, whichever days of the week they work.
Two other pro rata rules apply to holiday:
- Joining or leaving mid-year. A worker who starts after the leave year has begun gets the proportion of the year that remains. A leaver is paid for leave accrued but untaken, using the formula in regulation 14 of the Working Time Regulations 1998;
- Irregular hours and part-year workers. For leave years starting on or after 1 April 2024, these workers accrue holiday at 12.07% of hours worked in each pay period rather than taking a pro rata share of a fixed allowance.
Our guide to holiday pay covers how that leave is paid.
Pro rata pay and the minimum wage
A pro rata salary must still meet the minimum wage for every hour worked. From April 2026 the National Living Wage for workers aged 21 and over is £12.71 an hour. A salary of £13,000 for a 20-hour week works out at about £12.50 an hour (£13,000 ÷ 1,040 hours), which is below the rate. A salary of £14,000 for the same hours, about £13.46 an hour, is above it. Low FTE salaries scaled down for part-time roles are a common source of minimum wage underpayments. Our guide to the national minimum wage sets out the other age bands.
Pro rata outside payroll
Accountants use the same idea whenever a figure has to be apportioned over time. Common examples are spreading an annual insurance premium or software subscription across the months it covers, apportioning profits where an accounting period does not match a tax year, and splitting an annual fee when a client joins mid-year. The method does not change: take the share of the period, or of the activity, that applies, and multiply.
Sources: Part-time Workers Regulations 2000, regulation 5 and regulation 1; Working Time Regulations 1998, regulation 13A; GOV.UK: holiday entitlement; GOV.UK: National Minimum Wage and National Living Wage rates.
If you employ part-time staff, Acumon's outsourced payroll service handles pro rata pay, holiday accrual and minimum wage checks each pay run. See also our payroll services.