A pro rata salary is the full-time salary scaled to your hours: full-time pay multiplied by the hours or days you work, divided by the full-time hours or days. A £30,000 full-time job worked three days a week pays £18,000. The tax on it is not scaled in the same way, because the personal allowance stays at £12,570 however few hours you work, so part-time pay is taxed at a lower effective rate than the full-time figure suggests.
The figures below use the 2026/27 rates for England, Wales and Northern Ireland.
The three ways employers calculate it
By days. The most common method for office roles. Divide your days by the full-time five: three days is 3 ÷ 5, or 60%, of the full-time salary.
By hours. Used wherever the full-time week is defined in hours, typically 37.5 or 40. Divide your contracted hours by the full-time hours: 25 hours against a 37.5 hour week is 66.7%, so a £30,000 full-time salary becomes £20,000. Always ask what the full-time figure is, because 25 hours against a 40 hour week is only 62.5%, or £18,750.
By weeks, for term-time-only roles. School support staff and some college and nursery roles are paid for the weeks worked plus paid holiday, spread over twelve months. The formula is full-time salary × (weeks worked + holiday weeks) ÷ weeks in a year. On 39 working weeks with 5.6 weeks of holiday, using 52.14 weeks in the year, a £30,000 salary becomes £25,662 a year, or £2,138 a month. Some employers divide by 52 rather than 52.14, which gives £25,731, and some add bank holidays as extra paid weeks. The divisor and the holiday weeks are set out in the contract, and they matter: a difference of 1.6 weeks is worth about £920 a year on this salary. The pro rata salary calculator handles all three methods.
Why the tax is not pro rata
Income tax and National Insurance are charged on what you actually earn, and the tax-free personal allowance of £12,570 is not reduced for part-time work. A part-time worker therefore keeps a larger share of gross pay than a full-time colleague on the same hourly rate.
| Days a week | Gross pay | Income tax | National Insurance | Take-home | Deductions |
|---|---|---|---|---|---|
| 1 | £6,000 | £0 | £0 | £6,000 | 0% |
| 2 | £12,000 | £0 | £0 | £12,000 | 0% |
| 3 | £18,000 | £1,086 | £434 | £16,480 | 8.4% |
| 4 | £24,000 | £2,286 | £914 | £20,800 | 13.3% |
| 5 | £30,000 | £3,486 | £1,394 | £25,120 | 16.3% |
Three days on a £30,000 role pays 60% of the full-time salary but 66% of the full-time take-home. Two days pays 40% of the salary and keeps all of it. This is also why a job share between two people costs the employer the same salary but leaves the pair with more take-home in total than one full-time worker. The take-home pay calculator gives the figure for any part-time salary.
Reverse pro rata: from part-time pay to full-time equivalent
Job adverts, pay bands and public sector scales quote the full-time equivalent, so to compare a part-time salary with them you reverse the calculation: full-time equivalent = your salary × full-time hours ÷ your hours.
- £18,000 for three days a week: £18,000 × 5 ÷ 3 = £30,000 full-time equivalent.
- £21,000 for 30 hours against a 37.5 hour week: £21,000 × 37.5 ÷ 30 = £26,250.
- A term-time-only salary of £25,662 on 39 weeks plus 5.6 weeks holiday: £25,662 × 52.14 ÷ 44.6 = £30,000.
The full-time equivalent is the number to use when comparing offers or checking a pay band. It is not the number a mortgage lender uses: affordability is assessed on the pay you actually receive.
What else is pro rata, and what is not
Scaled to your hours: holiday entitlement (5.6 weeks of your working pattern, so 16.8 days for three days a week), bonuses expressed as a percentage of salary, pension contributions expressed as a percentage, and any benefit the contract says is pro rata, such as a car allowance.
Not scaled: the personal allowance, the National Insurance thresholds (which apply per pay period to your actual pay), the £10,000 auto-enrolment trigger (assessed on your actual pay in that job), student loan thresholds (applied to actual pay), and statutory payments such as sick pay, which have their own rules. A part-time worker paid £9,500 in a job is not automatically enrolled in the pension, even if the full-time equivalent is far higher, although they can ask to join.
Worked example
A full-time post is advertised at £30,000 for 37.5 hours. You agree 30 hours a week over four days. The pro rata salary is £30,000 × 30 ÷ 37.5 = £24,000. Income tax is £2,286, National Insurance £914, and take-home pay £20,800 a year, £1,733 a month. Holiday is 5.6 × 4 = 22.4 days a year. If the role were term-time-only on the same hours, 39 weeks plus 5.6 weeks holiday over 52.14, the salary would be £24,000 × 44.6 ÷ 52.14 = £20,530, paid as £1,711 a month across the year.
Common questions
How do I work out my pro rata salary? Multiply the full-time salary by your hours and divide by the full-time hours. For days, multiply by your days and divide by five. Check which full-time hours figure the employer uses.
Is holiday pro rata for part-time workers? Yes. The statutory minimum is 5.6 weeks of your own working pattern, so three days a week gives 16.8 days a year. Bank holidays are usually included in that figure rather than added to it.
Is tax pro rata? No. You are taxed on what you actually earn, with the full £12,570 allowance, so a part-time salary is taxed at a lower effective rate than the full-time equivalent.
How is a term-time-only salary calculated? Full-time salary × (weeks worked + paid holiday weeks) ÷ weeks in the year, usually 52.14. The result is paid in twelve equal monthly instalments. The contract sets the divisor and the holiday weeks.
What does full-time equivalent mean? The salary the role would pay if worked full time. It is the figure quoted in pay scales and adverts, and the one to compare when weighing job offers.
Does part-time work affect my State Pension? Only if pay in a job falls below the lower earnings limit of £129 a week (about £6,700 a year), below which the year does not count towards the State Pension unless you qualify for credits. Above that, a part-time year counts in full.
Information, not financial advice. Figures use the 2026/27 rates for England, Wales and Northern Ireland and are estimates to help you understand the rules. Contracts set the exact pro rata method, so check yours, and check tax figures against gov.uk before acting on them.