How this calculator works
Your pro rata salary is your full-time salary multiplied by the share of full-time hours you will work: 80% if you dial down by a fifth, 60% if you dial down by two-fifths. The calculator then takes off income tax, National Insurance, your pension contribution and any student loan to show what lands in your account.
It uses the 2026 to 2027 UK tax year: a £12,570 personal allowance (reduced by £1 for every £2 earned over £100,000), the income tax bands for England, Wales and Northern Ireland or for Scotland, and employee National Insurance of 8% between £12,570 and £50,270 and 2% above that.
It assumes a standard tax code, one job, and a pension contribution worked out on your whole salary. Your payslip can differ if your scheme uses “qualifying earnings”, you have benefits in kind, or you are already drawing a pension.
Why take-home falls by less than your hours
When you cut your days, the pay you give up is the top slice of your salary, which is the most heavily taxed part. So a 20% cut in hours usually costs less than 20% of your take-home pay.
Here is what that looks like for three salaries in England, with a 5% pension contribution under relief at source.
| Full-time salary | Full-time | 80% | 60% | Take-home kept at 60% |
|---|---|---|---|---|
| £30,000 | £23,920 | £19,840 | £15,760 | 66% |
| £45,000 | £34,120 | £28,000 | £21,880 | 64% |
| £60,000 | £42,957 | £36,160 | £28,000 | 65% |
At 60% you give up 40% of your working time but keep around two-thirds of your take-home pay. That is the core trade at the heart of a glide into semi-retirement: more time back than money lost.
Worked example
This is an example, not a real person. Jo earns £45,000 full-time in England, pays 5% into a workplace pension under relief at source, and is thinking about dialling down to 60% of full-time, for example fewer or shorter days.
- Pro rata salary: 60% of £45,000 = £27,000 a year.
- Take-home: falls from £34,120 to £21,880 a year, about £1,020 less each month.
- Each 10% Jo dials down costs about £255 a month in take-home pay.
- Time back: the equivalent of 104 working days a year, before holidays.
- Pension: Jo’s own contribution falls from £2,250 to £1,350 a year, and an employer contribution would usually fall in step.
Questions people ask
How do I work out a pro rata salary?
Divide your full-time salary by your full-time days and multiply by the days you will work. For example, £45,000 at 3 days out of 5 is £45,000 ÷ 5 × 3 = £27,000 a year before tax.
If I work 4 days a week, do I get 80% of my take-home pay?
Usually a bit more. Your gross pay falls to 80%, but more of what you lose would have been taxed, so take-home typically falls by less. On £45,000 with a 5% pension, a 4-day week keeps about 82% of take-home pay.
Will I pay less tax working part-time?
You pay less tax in pounds because you earn less. Everyone gets the same £12,570 personal allowance, so a larger share of a smaller salary is tax-free. If going part-time takes you below £50,270 you may also drop out of the higher rate band.
Does working part-time affect my State Pension?
Not if you still earn above the National Insurance lower earnings limit, because each year you do counts as a qualifying year. Check your National Insurance record on GOV.UK if your earnings will be low.
Can I ask my employer to work fewer days?
Yes. In Great Britain every employee can make a statutory flexible working request from their first day in a job, up to two in any 12 months. Your employer must consider it reasonably and reply within two months. GOV.UK explains how.
Is a 4-day week the same as compressed hours?
No. Compressed hours means working your full hours in four longer days for full pay. A part-time 4-day week means fewer hours for pro rata pay. This calculator shows the part-time version.
Guidance, not advice. This tool gives general guidance based on the information you enter. It is not financial advice. For free, impartial help, visit MoneyHelper.
Sources: GOV.UK: Rates and thresholds for employers 2026 to 2027 · GOV.UK: Flexible working · MoneyHelper.
Reviewed on 7 October 2026 · How our tools work