ProRata CalculateReverse Pro Rata Calculator — Hours Needed for the Pay You Want
Work out how many hours you need for the pay you want. Enter the role’s full-time salary and your target pay, and this calculator works backwards to the hours.
Reverse Pro Rata Calculator
The hourly rate of the full-time role decides everything — the calculator derives it, then divides your target by it.
When working backwards is the right move
Three situations call for the reverse sum. The first is budgeting a reduction: you know the household needs at least a certain income, so the question is not “what does 24 hours pay?” but “what is the fewest hours that still pays enough?” The second is comparing two adverts with different salaries and different hours — converting both into the hours each would demand for the same target pay exposes which rate is genuinely better. The third is checking a “salary on application” role after an interview: once you hear the full-time figure, you can price your own availability precisely before the negotiation call.
The same backwards division answers the mirror-image question people type as “how to work out full-time salary from pro rata”: your actual pay divided by your fraction reconstructs the full-time equivalent, which is the number to compare against market rates when deciding whether a part-time post is fairly priced.
Two reverse examples
Target £25,000 in a £38,750 role. The role pays £19.87 an hour at 37.5 hours full time. £25,000 ÷ £19.87 ÷ 52 = 24.19 hours a week, roughly three and a quarter standard days. If the employer offers 22.5 hours, you now know the shortfall is about £1,680 a year — a concrete figure to negotiate around.
Target £19,000 in a £27,750 role at 40 hours. The rate is £13.34 an hour; the hours needed are 27.39 a week (0.68 FTE). Offered as a four-day post of 32 hours it would overshoot the target, paying £22,200 — useful to know before asking for fewer hours than you actually need to give up.
Questions people ask
Divide your actual pay by your fraction. Earning £17,774 at 0.66 of a role (hours and weeks combined) implies a full-time equivalent of about £26,931. Equivalently, divide your pay by your FTE. This is the check to run when an advert quotes the pro rata figure only and hides the full-time salary.
At a full-time salary of £38,750 over 37.5 hours, £25,000 needs a fraction of 0.6452 — about 24.2 hours a week. Type your own full-time salary into the calculator: the answer moves with the rate, because hours buy pay at the role’s hourly rate, not at a universal one.
Then the target cannot be reached inside that role at that rate — the calculator flags it rather than pretending otherwise. Your options are a higher-paid role, overtime if it is offered at a genuine rate, or a second income. It is better to learn that from arithmetic than from an overdraft.
Yes, and it reframes the conversation usefully. Instead of asking for “a bit more”, you can say: at the advertised rate, the hours on offer produce £X, and I need £Y, which is Z hours. Managers respond better to a gap expressed in hours, because hours are the thing they can actually adjust.
The calculator works in gross pay, because hours are bought with gross pay. To see what a target take-home implies, add roughly the tax and National Insurance for that band — or run candidate hours through the salary calculator, whose take-home panel works the other way, and adjust until the net figure matches your target.
Rates used: UK tax year 2026/27 · Last reviewed: October 2026. Calculations run in your browser — nothing you type is sent anywhere or stored by us.