Pro Rata Pay Calculator
Use this UK pro rata pay calculator to work out part-time pay from working days per week. Pro rata pay = full-time salary × part-time days ÷ full-time days. £40,000 × 3 ÷ 5 = £24,000. Shows monthly and weekly gross. Estimates only.
UK pro rata pay calculator for contracts framed around working days per week, such as a three-day week against a five-day full-time week. Enter the full-time salary and both day counts to see annual, monthly and weekly gross pay.
Note: Figures are gross (before Income Tax, National Insurance and pension contributions).
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What this calculator does
Returns pro rata annual, monthly and weekly gross pay plus the working percentage, calculated from a full-time annual salary and full-time vs part-time working days per week.
Who it is for
UK employees on day-based contracts (typical in education, healthcare, accountancy and consulting), HR teams pricing four-day-week or three-day-week offers, and people comparing day-based pro rata offers.
How to use it
Enter the full-time annual salary, full-time working days per week (usually 5) and part-time working days per week (e.g. 3). Results update instantly with annual, monthly and weekly gross figures and the working percentage.
How the calculation works
Pro rata annual pay = full-time salary × part-time days ÷ full-time days. Monthly = annual ÷ 12. Weekly = annual ÷ 52. Working percentage = part-time days ÷ full-time days × 100.
Worked example
£40,000 full-time, 5 full-time days, 3 part-time days. Pro rata annual = £40,000 × 3 ÷ 5 = £24,000. Monthly ≈ £2,000. Weekly ≈ £461.54. Working percentage = 60.0%.
Assumptions and limitations
- Gross pay only — no Income Tax, NI or pension deductions
- Assumes equal-length working days
- Does not include bonuses, overtime or allowances
- Some sectors treat a full-time week as 6 days — adjust the full-time days field to match your contract
Frequently asked questions
How do I work out pro rata pay by days?
Multiply the full-time annual salary by your part-time days per week, then divide by the full-time days per week. £40,000 × 3 ÷ 5 = £24,000.
What if my employer uses a different full-time pattern?
Change the full-time days per week to match what your contract treats as full-time.
Is the result before tax?
Yes — gross pay before Income Tax, National Insurance and pension contributions.
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Sources and references
ACAS guidance on reduced-hours and part-time pay. GOV.UK: PAYE pay-period conversion guidance. General reference — not legal or tax advice.
Last updated
Last reviewed: 2026-05-20.