A pro rata pay calculation has three inputs (the full-time salary, the full-time hours, and yours) and two outputs people routinely mix up: the prorated gross, and what that gross keeps after tax. From a £30,000 full-time salary, four days a week gives £24,000 gross and £20,799.60 net in 2026/27; this page works each common basis so you can see which fraction fits your case.
By hours: the everyday case
Weekly hours over full-time hours. 25 hours against 37.5 is two-thirds: a £30,000 FTE becomes £20,000 gross. Because the fraction applies before tax, the net does not fall by two-thirds of the full-time net: the untouched £12,570 allowance covers proportionally more of a smaller gross, so the effective deduction rate drops from 16.27% at full hours to under that at reduced hours. Always quote both hour counts in writing; disputes are almost always about the denominator.
By days and by weeks: term-time and partial months
Days worked over contracted working days handles a mid-month start: joining on the 16th of a month with 22 working days, 11 of them yours, halves that month's pay. Weeks handle term-time contracts. 39 paid weeks over 52 (holiday pay is usually rolled in on top, and must be stated separately on the payslip). In each case the prorated gross is what PAYE sees, and the year's tax trues itself up automatically across the remaining pay periods.
A prorated salary at the year's end
Leaving part-way through the tax year, your final figure is the annual salary × months served ÷ 12, and your tax to date will often overshoot because PAYE assumed a full year: the refund arrives through the next employer's payroll or from HMRC directly. The calculator linked below shows the per-month net for any gross, which is the quickest way to check a final payslip against what the fraction says it should be.
Questions people ask about pro rata pay calculator
Pro rata pay calculator or salary calculator pro rata: is there a difference?
Same calculation, either word order: scale the salary by the time fraction, then run the tax. Both inputs and both steps are identical.
How is prorated holiday pay worked out?
The statutory minimum of 5.6 weeks scales by the same fraction as pay. A 0.6 contract accrues 0.6 × 5.6 weeks, at the part-time weekly rate.
Does a prorated salary use a special tax code?
No: the standard code applies and the allowance is spread across the year's pay periods by PAYE, whatever the fraction.