How to Work Out Pro Rata Salary

Before you calculate

Find three figures in the job offer or contract. Use the full-time salary for the same role, not a salary that has already been reduced for part-time work.

• The annual full-time gross salary, before tax and other deductions.
• The paid hours in a normal full-time week for that role.
• Your agreed paid hours per week, on the same basis.

Exclude unpaid breaks from both schedules. Do not assume every employer uses 40 hours. Acas explains that there is no single set number of hours defining full-time or part-time work. Acas guidance.

The calculation, step by step

1. Divide your hours by the full-time hours. In the first example, 22.5 ÷ 37.5 = 0.6. This is the full-time equivalent (FTE) ratio: 60% of the full-time schedule.
2. Multiply the annual full-time salary by that ratio. £30,000 × 0.6 = £18,000 annual gross pay.
3. For an equal monthly comparison, divide by 12: £18,000 ÷ 12 = £1,500. This is still gross pay, not the amount deposited into your bank account.

Keep the full ratio during the calculation and round the displayed money only at the end. Replacing 23.25 ÷ 37.5 with a rough percentage before multiplying can change the answer.

Worked examples

Three equal-length days instead of five

A £30,000 full-time role has five paid days of 7.5 hours, or 37.5 hours a week. Three of those days total 22.5 hours. The result is £18,000 annually and £1,500 monthly. The days shortcut, 3 ÷ 5, works here because every day has the same paid hours.

Four equal-length days instead of five

For a £42,000 role with 35 full-time hours, four 7-hour days total 28 hours. The ratio is 28 ÷ 35 = 0.8. Annual gross pay is £33,600 and equal monthly gross pay is £2,800. A different employer could use different hours for the same number of days.

When the working days are not equal

Suppose a £31,200 role uses 37.5 full-time hours. Your paid week is 8 + 8 + 7.25 = 23.25 hours. Use 23.25 ÷ 37.5 = 0.62, not a three-day assumption. The result is £19,344 annually and £1,612 monthly. Enter 7 hours 15 minutes as 7.25 hours, not 7.15.

Compressed hours are not fewer hours

Four 10-hour days total 40 hours, just as five 8-hour days do. At a £36,000 full-time salary for 40 hours, the ratio is 1.0 and the model returns £36,000, not £28,800. Compare the paid hours, not the number of days on the calendar.

Reading a salary advert

An advert saying “£30,000 FTE, pro rata” usually presents the full-time reference salary. Confirm the actual contracted salary with the employer. If an offer already states “actual annual salary £18,000” for the 22.5-hour pattern above, do not multiply that £18,000 by 0.6 again: that would reduce the pay twice.

For a reverse check, divide the actual annual gross salary by the FTE ratio: £18,000 ÷ 0.6 = £30,000. This check only works when both amounts use the same pay basis and the ratio is greater than zero.

What this calculation leaves out

Gross and net pay are different. GOV.UK distinguishes earnings before and after deductions on a payslip. Tax, National Insurance, pension and other deductions can change take-home pay; multiplying full-time net pay by an hours ratio is not a reliable substitute for a payroll calculation. Payslip guidance.

The calculator uses annual ÷ 52 for a weekly comparison and annual ÷ (52 × full-time hours) for a reference hourly rate. A payroll system may use another contract-specific basis. A four-weekly payment is not the same as a monthly payment.

• Term-time-only and part-year contracts need paid weeks and holiday arrangements as well as weekly hours. Do not apply this all-year model unchanged.
• Starting or leaving mid-month needs the employer’s partial-period payroll method. A weekly-hours ratio alone does not determine the first or last payslip.
• Bonuses, shift allowances, overtime and holiday entitlement are outside this calculation. Check their separate rules rather than assuming every payment scales the same way.

For a straightforward all-year contract, your next step is to confirm the three inputs, calculate the gross amount, then compare it with the offer or ask payroll to explain any difference.