Pro Rata Calculator (Part-Time Salary)

How to work out pro rata salary

The pro rata formula is simple: divide the full-time salary by the full-time hours, then multiply by the hours you actually work. For example, a £30,000 full-time salary on 37.5 hours a week works out at £18,000 pro rata for 22.5 hours (30,000 ÷ 37.5 × 22.5). The calculator below does this for you and then shows the tax, National Insurance and take-home pay on your pro rata amount.

Part-time salary calculator

This tool doubles as a part-time salary calculator: enter the advertised full-time salary and your part-time hours or days, and you get the equivalent part-time pay for 2026/27, including holiday-neutral monthly and weekly figures.

Use the pro rata salary calculator above

Type in the full-time salary, the standard full-time hours (or days) for the role and your own hours or days. The tool above returns your pro rata salary instantly, so you can sense-check an offer or compare two part-time jobs without doing the sums by hand.

How a pro rata salary is worked out

"Pro rata" is Latin for "in proportion". A pro rata salary is simply the full-time salary scaled down to the proportion of full-time hours or days you actually work. There is no special tax rule involved at this stage; it is plain arithmetic. The formula is:

Pro rata salary = Full-time salary × (your hours ÷ full-time hours)

You can run the same calculation using days instead of hours, which suits roles described as a number of days per week:

Pro rata salary = Full-time salary × (your days ÷ full-time days)

The fraction in brackets is your "full-time equivalent", or FTE. Someone working three days against a five-day week has an FTE of 0.6, so they earn 60% of the full-time salary. The trickiest part is knowing what "full-time" means for that employer. There is no single legal definition of full-time hours in the UK; it is set by the contract. Common full-time weeks are 35, 37.5 or 40 hours, so always check the advert or ask, because using the wrong denominator throws the whole figure out.

Once you have the pro rata gross salary, income tax and National Insurance are charged on that lower figure in the normal way. The same Personal Allowance of £12,570 applies whether you work full or part time, which is why part-time pay often suffers proportionally less tax. If you want the after-tax number, feed the pro rata result into our take-home pay calculator or the gross-to-net calculator.

Worked examples with the maths shown

Example 1 - dropping to part-time hours

Priya is offered a role advertised at £30,000 for a 37.5-hour full-time week, but she will work 22.5 hours. Her FTE is 22.5 ÷ 37.5 = 0.6.

• Pro rata salary = £30,000 × 0.6 = £18,000
• Income tax: taxable income £18,000 − £12,570 = £5,430, taxed at 20% = £1,086
• National Insurance: (£18,000 − £12,570) × 8% = £434.40
• Estimated take-home = £18,000 − £1,086 − £434.40 = £16,479.60 a year (about £1,373 a month)

Example 2 - a three-day week

Tom sees a £45,000 job based on a five-day week and negotiates three days. His FTE is 3 ÷ 5 = 0.6, so his pro rata salary is £45,000 × 0.6 = £27,000. On that, the basic-rate calculation gives income tax of (£27,000 − £12,570) × 20% = £2,886 and NI of (£27,000 − £12,570) × 8% = £1,154.40, leaving roughly £22,959.60 before any pension.

Example 3 - term-time only

School support staff are often paid pro rata for weeks worked. Say the full-time salary is £25,000 across 52 weeks, and the contract covers 39 working weeks plus 5.6 weeks of paid holiday (44.6 paid weeks). The FTE is 44.6 ÷ 52 = 0.858, giving a pro rata salary of £25,000 × 0.858 = £21,442. Term-time pay is fiddly precisely because holiday weeks have to be added back in, so always ask your employer how the weeks were counted.

2026/27 tax figures used in the examples

The pro rata calculation itself is tax-free arithmetic, but the take-home figures above use the 2026/27 thresholds for England, Wales and Northern Ireland. Scotland sets its own income tax bands, so a Scottish part-timer earning above the Personal Allowance may pay a slightly different amount; the figures below do not apply north of the border.

Source: gov.uk income tax rates and the 2026/27 rates and thresholds for employers, checked for the 2026/27 tax year. If you live in Scotland, use our Scotland tax calculator for the correct bands.

Pro rata pay beyond salary: what else gets scaled

Salary is not the only thing that goes pro rata. Your holiday entitlement, pension contributions and many benefits are usually proportioned to your hours too. A full-time worker gets a statutory minimum of 5.6 weeks' paid holiday; a part-timer gets 5.6 weeks of their working week, so a three-day-a-week employee is entitled to 16.8 days, not 28. Work out yours with the holiday entitlement calculator. If you are thinking in terms of an hourly figure rather than an annual one, the salary-to-hourly calculator converts between the two.

Bonuses, sick pay and notice periods can all be pro-rated as well, so read the contract carefully. The principle is the same throughout: take the full-time amount and multiply by your FTE.

Common mistakes to avoid

• Assuming the advert already shows part-time pay. Adverts that say "£28,000 pro rata" mean the full-time figure; your actual pay is lower. Always scale it before you accept.
• Guessing the full-time hours. Using 40 hours when the employer's full-time week is 37.5 understates your FTE and your pay. Confirm the denominator.
• Forgetting holiday weeks in term-time roles. Term-time pay should include paid statutory holiday, not just the weeks you are physically at work, so a 39-week role is paid across roughly 44.6 weeks.
• Expecting tax to halve when pay halves. Because the Personal Allowance stays at £12,570 regardless of hours, dropping from £30,000 to £18,000 cuts your income tax by far more than half. Part-time work is often more tax-efficient per pound than people expect.
• Overlooking the emergency tax code. Starting a part-time job mid-year can trigger a temporary code and over-deduction. Check yours and reclaim if needed with the emergency tax calculator.

For broader context on how part-time and flexible-working pay is protected, MoneyHelper's guidance on pay and deductions is a useful read, and gov.uk explains your statutory rights as a part-time worker.

These figures are estimates for guidance only and are not personal tax or financial advice. For a tailored answer, check your contract and speak to your employer or a qualified adviser.

Related calculators

Once you know your pro rata figure, line it up against other roles with the salary calculator for a full breakdown, or work out the deductions in detail using the income tax calculator. Comparing a pay change? The pay rise calculator shows the after-tax effect of a higher salary.