Key takeaways
- Part-time pay is not simply pro-rata take-home: at £24,000 you keep 83.7% of your pay, against 77.4% at £40,000 full-time.
- The £12,570 personal allowance applies in full whether you work five days or one — National Insurance starts at the same £12,570 and the pension band at the same £6,240.
- Dropping from £40,000 to £24,000 costs £10,880.00 a year of take-home pay — a real loss, though less than a naive three-fifths-of-take-home sum would suggest.
- A 37.5-hour week and a 40-hour week give different answers for the same hours: 20 hours is 0.533 of a 37.5-hour week but exactly half of a 40-hour week.
Part-time pay is not simply pro-rata take-home. At £24,000 you keep 83.7% of your pay, against 77.4% at £40,000 full-time — because the £12,570 personal allowance does not shrink when your hours do.
Going part-time is one of the biggest financial decisions most people make, and it is usually made with bad numbers. Someone offers you three days a week on a £40,000 job, and you work out three fifths of your current take-home pay and hope for the best. That is the wrong sum. Your salary is pro-rata, but your tax is not — the personal allowance, the NI threshold and the pension band are all fixed, so a part-time salary keeps a bigger share of itself than a full-time one. This article does the maths properly, at four real patterns, so you can decide with the true figure.
The rule: salary is pro-rata, tax is not
Your actual salary is simple: full-time salary multiplied by the fraction you work. Three days of five is 0.6; four days is 0.8; half-time is 0.5. A £40,000 job at three days a week is £24,000. A £30,000 job at 20 hours of a 37.5-hour week is £16,000. Term-time only — 39 weeks of 52 — is 0.75, so a £30,000 job becomes £22,500.
What is not simple is the take-home pay, because tax is worked out on the actual salary from scratch. The £12,570 personal allowance applies in full whether you work five days or one. National Insurance starts at the same £12,570. The pension band starts at the same £6,240. All of those fixed thresholds are a bigger share of a smaller salary, so less of your pay is taxed at all. That is why part-time work pays better per hour, after tax, than the same job full-time.
Four patterns, worked out
All figures below use the usual auto-enrolment pension (5% of qualifying earnings) and no student loan.
| Pattern | Actual salary | Take-home / year | Take-home / month | You keep |
|---|---|---|---|---|
| £40,000 full-time, 3 days a week | £24,000.00 | £20,089.20 | £1,674.10 | 83.7% |
| £30,000 full-time, 20 of 37.5 hrs/wk | £16,000.00 | £14,649.20 | £1,220.77 | 91.6% |
| £45,000 full-time, half-time | £22,500.00 | £19,069.20 | £1,589.10 | 84.8% |
| £35,000 full-time, 4 days a week | £28,000.00 | £22,809.20 | £1,900.77 | 81.5% |
Read the last column carefully. At £40,000 full-time you keep 77.4% of your pay (£30,969.20 of take-home). At £24,000 part-time you keep 83.7%. At £16,000 you keep 91.6% — because most of that salary sits inside the personal allowance, and only £2,942.00 of it is taxable at all after pension and allowance. The smaller the salary, the bigger the share you keep. That is the honest answer to "is part-time worth it": you lose less than the headline suggests, because the tax system is on your side at lower pay.
None of this means part-time is free. Dropping from £40,000 to £24,000 costs £10,880.00 a year of take-home pay (£30,969.20 down to £20,089.20). That is a real loss, and it is bigger than the salary loss in percentage terms is smaller — the point is only that it is less than a naive three-fifths-of-take-home sum would suggest. A naive sum would predict £18,581.52 (three fifths of £30,969.20); the true figure is £20,089.20, which is £1,507.68 a year better than the naive guess.
Hours, days and fractions — one maths, three languages
Part-time is talked about in three different languages, and they cause endless confusion. Hours: 22.5 of a 37.5-hour week. Days: 3 of 5. Fractions: 0.6 FTE. They are the same thing, and the calculator on this site accepts all three — but only if the full-time week is defined. A 37.5-hour week and a 40-hour week give different answers for the same hours: 20 hours is 0.533 of a 37.5-hour week but exactly half of a 40-hour week. Always confirm the full-time hours before you agree anything.
Term-time only is the fourth language, and it catches school staff out most often. A teaching assistant on £30,000 full-time, working 39 weeks a year, earns £22,500 — not £30,000 spread over fewer weeks, and not £30,000 minus holiday. Some contracts add paid holiday weeks on top of the 39, which changes the fraction; if yours does, use the custom fraction in the pro-rata calculator rather than the 39-week shortcut.
What else changes when you go part-time
Pension is the first thing to check. Auto-enrolment applies on the same terms, but the qualifying-earnings band is worked out on your actual pay — at £24,000 your employee pension is £888.00 a year. If your part-time pay falls below the £10,000 auto-enrolment trigger, your employer does not have to enrol you at all, though you can usually opt in. Below £6,240 of qualifying earnings there is no pension to pay. Check what your scheme actually does, because the difference between being enrolled and not being enrolled is thousands of pounds of retirement savings.
Student loan is the second. The deduction is 9% above your plan threshold, and the threshold does not change for part-time workers. At £24,000 a Plan 2 borrower pays nothing (the threshold is £29,385), while a Plan 5 borrower pays 9% of nothing either — £24,000 is below the £25,000 Plan 5 threshold too. Drop below the threshold and the loan deduction stops entirely, which is another reason part-time take-home is better than the naive figure.
Benefits tied to salary are the third. Statutory maternity pay, statutory sick pay and employer sick pay are all based on your earnings, so they fall with your salary. Some employers pro-rate holiday, bonuses and even training budgets. None of this is a reason to refuse part-time work, but all of it belongs in the decision — a salary is not just the monthly number.
Deciding with the true figure
The question is never really "what is my part-time salary". It is "can I afford to live on it". Work out the true take-home figure first, using the calculators below, and budget on that — not on a guess, and not on three fifths of your current pay. Then check the pension position, the student loan position, and any benefit that depends on your salary. If the numbers work, part-time is often a better deal than people expect, because the tax system quietly gives some of the money back. If they do not work, you will at least know by how much, and you can negotiate from a position of knowledge rather than hope.
Work out your part-time pay
Enter your full-time salary and hours in the part-time salary calculator, or your contracted fraction in the pro-rata salary calculator — both show your real take-home next to the full-time figure. For the full picture, see the take-home pay calculator and the 2026/27 rates behind every figure on this page.
Questions
What is my salary if I work 3 days a week on £40,000 full-time?
£24,000 a year — three fifths of £40,000. Your take-home pay would be £20,089.20 a year (£1,674.10 a month) with the usual auto-enrolment pension, against £30,969.20 a year full-time.
Is part-time take-home pay just pro-rata?
No — and that is good news. Because the £12,570 personal allowance does not shrink when you work fewer hours, you keep a bigger share of each pound part-time. At £24,000 you keep 83.7% of your pay; at £40,000 full-time you keep 77.4%.
What does 0.8 FTE mean?
FTE means full-time equivalent. 0.8 FTE is 80% of a full-time job — usually four days a week. On a £30,000 full-time salary, 0.8 FTE is £24,000 a year, with take-home pay of £20,089.20 a year.
Decide with the true figure
Work out the true take-home figure first, using the calculators below, and budget on that — not on a guess, and not on three fifths of your current pay.
Figures are for tax year 2026/27, tax code 1257L, England, Wales or Northern Ireland, auto-enrolment pension at 5% of qualifying earnings, no student loan unless stated. Rates: GOV.UK — last checked 5 November 2026. This site is not affiliated with HMRC or GOV.UK. Figures are estimates for guidance, not financial advice.