Pro rata salary calculator
A pro rata salary is the full-time pay scaled to the hours you actually work: full-time salary × your hours ÷ full-time hours. Enter both and this calculator shows the pro rata figure, and, unlike most, what it comes to after tax, which is not simply scaled down.
2026/27 rates, checked 2026-08-28. Assumes the standard 1257L tax code, no pension and no student loan.
Working 22.5 of 37.5 hours (60% of full time)
£18,000 a year
£16,479.60 take-home, £1,373.30 a month
Full-time vs your hours
Tax is not pro-rated. Your personal allowance stays £12,570.00 however few hours you work, so part-time pay is taxed more lightly per pound.
| Full-time | Your hours | |
|---|---|---|
| Gross salary | £30,000.00 | £18,000.00 |
| Income tax | −£3,486.00 | −£1,086.00 |
| National Insurance | −£1,394.40 | −£434.40 |
| Take-home | £25,119.60 | £16,479.60 |
| Monthly take-home | £2,093.30 | £1,373.30 |
| You keep | 83.7% | 91.6% |
You earn 60% of the full-time salary but keep 66% of the full-time take-home, the difference is the allowance working harder for you.
How pro rata pay is worked out
A job advertised at “£30,000 pro rata” pays £30,000 only for full-time hours, usually 37.5 a week, sometimes 35 or 40. Work 22.5 hours (three days) against a 37.5-hour full-time week and you are paid 60% of it: £18,000 a year. The same scaling applies whether the arrangement is fewer hours per day, fewer days per week, or a job share.
Statutory holiday scales the same way: the 5.6-week minimum becomes 5.6 weeks of your working week, so a three-day week carries 16.8 days rather than 28.
Why part-time pay is taxed more lightly
Your salary is pro-rated; your tax-free personal allowance is not. It stays £12,570.00 whether you work five days or two. On the £18,000 example, the allowance shelters 70% of pay rather than 42%, so the part-timer keeps £16,479.60 of £18,000, 91.6% of gross, against 83.7% for the full-timer. National Insurance behaves the same way, because its £12,570 threshold is not pro-rated either.
The practical consequence: dropping from five days to four costs less take-home than one-fifth. The days you give up are your most heavily taxed pounds.
What this calculator assumes
- The standard 1257L tax code, and that this is your only job.
- Pay spread evenly across the year. Term-time-only contracts are usually annualised by the employer and need their formula, not this one.
- No pension or student loan, add those on the main calculator with your pro rata figure.
2026/27 HMRC rates, checked 2026-08-28. Sources and method on the about page.