Pro Rata Calculator: Part-Time Salary & FTE

For a quick sanity check, the pro rata fraction is just the full-time equivalent (FTE): 22.5 ÷ 37.5 = 0.6, so 0.6 of the full-time salary. This works whether the part-time pattern is three days a week, term-time only, or job-share.

A pro rata salary is the proportion of a full-time salary that someone earns when they work fewer hours or fewer weeks than the full-time equivalent. The phrase comes from the Latin "pro rata" — *in proportion*. A part-time employee working half the standard hours is paid half the full-time salary; a term-time worker paid over 12 months gets 39/52 of the full-time figure.

Pro rata is the default in UK employment law for any contractual entitlement that scales with hours or weeks: salary, holiday, maternity pay, redundancy, and notice periods all follow the same proportion. If the full-time role is £40,000 over 37.5 hours, the pro rata salary for 25 hours a week is £26,667 — and the same proportion applies to everything else attached to the job.

There are two equivalent ways to write the formula.

• Hours ratio: pro rata salary = full-time salary × (part-time hours ÷ full-time hours)
• FTE fraction: pro rata salary = full-time salary × FTE, where FTE = part-time hours ÷ full-time hours

The FTE fraction is the same fraction you use for pension contributions, employer National Insurance, and holiday entitlement. It is also the figure to use for an annualised-hours contract: spread the FTE salary evenly across 12 monthly payslips.

When the part-time pattern is irregular (for example, school hours only, or seasonal work), use the contracted weekly hours averaged over a full year. A term-time-only worker paid over 12 months is typically 39/52 = 0.75 FTE, not the simple term-time / full-time-week ratio.

Three worked examples using the formula in this pro rata calculator. The chart below visualises how the pro rata figure changes at common FTE fractions.

• £30,000 full-time at 0.5 FTE: a £30,000 role based on 37.5 hours a week, working half the hours. Pro rata salary = £30,000 × (18.75 ÷ 37.5) = £15,000 a year.
• £40,000 full-time, 25 hours instead of 37.5: Pro rata salary = £40,000 × (25 ÷ 37.5) = £26,667 a year.
• £45,000 full-time, term-time only paid over 12 months: FTE = 39 ÷ 52 = 0.75. Pro rata salary = £45,000 × 0.75 = £33,750 a year.

In every case the result is gross annual pay. Use the take-home pay calculator to see the income tax and employee National Insurance that would be deducted through PAYE on that figure.

The pro rata formula covers the most common UK working patterns, but each has a small wrinkle worth knowing. The table below sets them out side by side.

A part-time worker on a regular hours pattern is the most straightforward case — this is what the pro rata salary calculator does. A job-share is two people each taking part of the full-time hours, usually splitting the role 50/50, with each paid the FTE fraction that matches their share. A term-time-only worker is paid over 12 months for a role that only runs for the school year, so FTE = 39/52. An annualised-hours contract is paid the same amount each month regardless of how the hours fall, smoothing irregular patterns. Zero-hours workers do not have a pro rata annual salary until a regular pattern emerges.

Salary is only part of the picture. Holiday entitlement, pension contributions and statutory pay are also pro rated.

• Holiday entitlement. The statutory 5.6 weeks of paid leave scales with the working pattern. A 5-day-a-week full-timer gets 28 days; a 3-day-a-week part-timer gets 16.8 days (3 × 5.6). Bank holidays can be included in that allowance or paid on top — the contract decides. From April 2024, irregular-hours workers accrue 12.07% of hours worked as holiday.
• Pension contributions. Auto-enrolment contributions are based on qualifying earnings, so they fall automatically as pay falls. A 0.5 FTE employee earning £15,000 pays 5% (£750) and the employer adds 3% (£450) on the same basis. Use the workplace pension calculator to model the figures.
• Statutory pay (SSP, SMP, etc.). The entitlement still applies to part-timers, but the average weekly earnings used to calculate the amount are based on actual earnings, which are already pro rated. A 0.5 FTE employee earning £15,000 will usually receive less SSP or SMP than a full-timer on £30,000 because the cap is 80% of their own average weekly earnings.
• Notice and redundancy. Statutory notice and redundancy payments are pro rated by the same FTE fraction. A 0.5 FTE employee with four years' service is entitled to five weeks' notice at half the full-time weekly pay.

Most pro rata errors are arithmetic rather than legal, but they create real pay disputes. Watch out for these.

• Using days instead of hours. A 3-day week is not necessarily 0.6 FTE. Always convert to contracted hours and divide by the full-time hours.
• Forgetting to subtract unpaid breaks. A 9-to-5 role with an hour's unpaid lunch is 35 hours, not 40. The full-time comparator must use the same convention.
• Counting overtime. Occasional extra hours should not appear in the pro rata calculation; the FTE is fixed at the contracted hours.
• Mixing monthly and annual figures. Annualise the full-time salary first, then apply the FTE. A monthly figure ÷ 12 × 12 is the same number, but mixing £2,500/month and £35,000/year will silently produce the wrong answer.
• Paying term-time only as a fraction of the school year, not the calendar year. A 39-week worker paid over 12 months is 39/52 FTE = 0.75, not 0.75 of 52 weeks of pay.
• Ignoring pension thresholds. A 0.4 FTE employee earning £8,000 falls below the £10,000 auto-enrolment trigger and is not entitled to be enrolled — the pro rata salary drives this, not the FTE fraction.

If you set pro rata salaries, the legal risks sit around transparency and consistency, not the maths.

• Put the FTE in the contract or written statement. From day one, the part-time contract should state the full-time equivalent salary, the actual hours, and the FTE fraction. The payslip should show the pro rata figure clearly.
• Use the same hours convention for everyone. If full-time is 37.5 hours, every part-time figure should be derived from 37.5. Mixing 35 and 37.5 in the same organisation invites equal-pay claims.
• Review when roles change. If the full-time hours, full-time salary, or part-time hours change, the pro rata figure should be re-calculated. A new contract or variation letter should record the change.
• Don't forget pension and statutory pay. Re-calculating the salary but leaving the pension contribution on the old figure is a common payroll mistake — and one HMRC will pick up on an audit.
• Equal treatment. Under the Part-Time Workers Regulations 2000, less favourable treatment of a part-timer compared to a comparable full-timer must be objectively justified, otherwise it is automatically unlawful.

The free pro rata pay calculator above handles the arithmetic; the discipline is making sure the figures feeding into it are current and the contract reflects the result.

Three numbers in, one number out. Enter the full-time annual salary, the full-time weekly hours (typically 37.5), and the actual weekly hours. The pro rata calculator returns the gross annual salary for the part-time role using the hours-ratio formula. Divide actual by full-time to get the FTE; multiply the FTE by the full-time salary to get the pro rata figure. The same fraction then drives holiday entitlement, pension contributions, and statutory pay — so recalculate everything together when hours change.