Quick answer
Pro-rata salary = full-time salary × your hours ÷ full-time hours. For example, 22.5 hours of a 37.5-hour, £30,000 job is 60% of full-time, so the pro-rata salary is £18,000 a year before tax. The hourly rate stays the same as full-time.
What "pro rata" means
"Pro rata" is Latin for "in proportion". In a job advert, "£30,000 pro rata" means £30,000 is what a full-time employee earns; a part-timer is paid the same rate for fewer hours, so the salary is scaled down to match.
The pro-rata formula
Pro-rata salary = full-time salary × (your hours ÷ full-time hours). If you're paid by days, use days instead of hours. The share you get is the same either way, as long as every day is the same length.
Example: by hours
A £30,000 job with a 37.5-hour week, worked for 22.5 hours: 22.5 ÷ 37.5 = 0.6, so the pro-rata salary is £18,000 a year, or £1,500 a month. The hourly rate is £15.38, the same as full-time.
Example: by days
A £42,000 job, 3 days of a 5-day week: 3 ÷ 5 = 0.6, giving £25,200 a year.
Why the full-time hours matter
The same "£30,000 pro rata" pays differently depending on the employer's full-time week. For 20 hours a week:
| Full-time week | Your share | Pro-rata salary | Hourly rate |
|---|---|---|---|
| 35 hours | 57% | £17,143 | £16.48 |
| 40 hours | 50% | £15,000 | £14.42 |
Before you accept an offer, ask which full-time hours the salary is based on.
Pro-rata pay after tax
The pro-rata figure is gross pay. Because the first £12,570 of income is tax-free, part-timers often keep a bigger share of their gross pay than full-timers. Our part-time job calculator shows the pro-rata salary, take-home pay and holiday side by side with the full-time version.
Term-time and part-year contracts
Some jobs, especially in schools, are paid for fewer weeks than the full year. Those salaries are usually pro-rated twice: once for hours and again for paid weeks (working weeks plus holiday). Employers use different formulas, so check how your contract works out "weeks paid". This calculator covers hours and days only.
Your rights as a part-time worker
Part-time workers should get the same hourly pay as comparable full-time colleagues, the same access to pension schemes, and holiday in proportion to the hours they work. You also have the right to ask your employer for flexible working, including part-time hours.
Sources: gov.uk part-time worker rights · gov.uk National Minimum Wage rates · gov.uk flexible working · gov.uk holiday entitlement