Monthly Pro Rata Pay Calculator
Use this monthly pro rata pay calculator to estimate part-time monthly gross pay. Monthly = (full-time salary × part-time hours ÷ full-time hours) ÷ 12. £30,000 × 22.5 ÷ 37.5 ÷ 12 = £1,500/month. Gross only — no tax or NI.
UK monthly pro rata pay calculator. Enter a full-time annual salary and your weekly hours to see the monthly gross figure most UK employees actually budget around, with annual and weekly shown for reference.
Note: Gross figures only — no tax, National Insurance or pension deductions.
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What this calculator does
Returns pro rata monthly gross pay, annual gross and weekly gross from a full-time annual salary, full-time weekly hours and part-time weekly hours.
Who it is for
UK part-time and reduced-hours employees who budget month-to-month, returners after parental leave, and HR teams quoting a clear monthly pro rata figure on flexible-working offers.
How to use it
Enter the full-time annual salary, full-time weekly hours and your part-time weekly hours. The monthly gross figure is shown as the headline, with annual and weekly underneath.
How the calculation works
Pro rata annual = full-time salary × part-time hours ÷ full-time hours. Monthly gross = pro rata annual ÷ 12 calendar months. Weekly gross = pro rata annual ÷ 52 weeks.
Worked example
£30,000 full-time, 37.5 full-time hours, 22.5 part-time hours. Pro rata annual = £18,000. Monthly gross = £18,000 ÷ 12 = £1,500. Weekly gross ≈ £346.15.
Assumptions and limitations
- Gross monthly pay only — Income Tax, National Insurance and pension contributions are not deducted
- Uses annual ÷ 12 for monthly (calendar months, not lunar)
- Does not handle salary sacrifice — subtract the sacrifice amount from your full-time salary first if you want the post-sacrifice figure
- Does not include bonuses, overtime, allowances or shift premiums
Frequently asked questions
How is monthly pro rata pay calculated?
Work out the pro rata annual salary first (full-time salary × part-time hours ÷ full-time hours), then divide by 12.
Is this take-home pay?
No — it is gross monthly pay. Use a take-home salary calculator for net pay.
Does it handle salary sacrifice?
Not directly. Subtract the sacrifice amount from the full-time salary first to see the post-sacrifice pro rata figure.
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Sources and references
GOV.UK: PAYE pay-period guidance for monthly and weekly gross pay. ACAS: Reduced-hours and part-time working guidance. General reference — not legal or tax advice.
Last updated
Last reviewed: 2026-05-20.