Going part-time, or comparing a job advertised on a full-time salary? Enter the full-time pay and hours alongside your own hours to see your pro-rata salary and what you keep after tax and National Insurance.
England, Wales & NI · 2026/27
“Pro rata” is Latin for “in proportion”. When a job is advertised at a full-time salary but you work fewer hours, your pay is scaled down in proportion to the hours you actually do. The formula is: pro-rata salary = full-time salary × (your hours ÷ full-time hours).
So a role paying £30,000 for a 37.5-hour week, worked at 22.5 hours, gives £30,000 × (22.5 ÷ 37.5) = £18,000. That £18,000 is your real gross salary, and HMRC taxes it as such — not the headline full-time figure.
Suppose a £40,000 full-time role is based on a 5-day, 37.5-hour week and you work 3 days (22.5 hours):
Holiday is pro-rated too: statutory 5.6 weeks scales to your working pattern. See the after-tax picture in more depth with the income tax calculator.
Pro-rata figures appear in part-time job adverts, term-time-only roles, job shares, phased retirement and any change to contracted hours. Always confirm what hours the employer treats as full-time, because that baseline drives the whole calculation. Comparing two part-time offers? Convert each to an hourly rate first.
Full-time salary × (your hours ÷ full-time hours). A £30,000 role at 21 of 35 hours becomes £30,000 × 21/35 = £18,000.
Tax is on the salary you actually receive. A lower pro-rata salary leaves more covered by the £12,570 Personal Allowance, so the effective tax rate is usually lower.
Yes. The statutory 5.6 weeks of holiday is scaled to your part-time pattern, so fewer working days earn proportionally fewer paid holiday days.
Whatever your employer counts as full-time — often 35, 37.5 or 40 hours. The result is the ratio of your hours to that baseline.