Pro-rata salary calculator

The Latin phrase means "in proportion", and that is all the calculation is: take the full-time salary, work out what share of full-time hours you do, and apply that share to the money. This tool asks for three things, the full-time annual salary, the hours a full-time person works in a week, and the hours you work, and returns your pro-rata annual salary along with the monthly and weekly equivalents and the percentage of full time you are on. The reason it matters is that job adverts almost always quote the full-time salary even when the role is advertised as part time, followed by the words "pro rata". A post advertised at 35,000 pro rata for 22.5 hours against a 37.5 hour full week is not a 35,000 job; it is a 21,000 one, because 22.5 divided by 37.5 is 0.6, and 0.6 of 35,000 is 21,000. People routinely misread that line and expect the higher figure to land in their account, so seeing the real number early avoids a nasty surprise on the first payday. The maths is deliberately simple, and knowing it lets you sanity-check any offer in your head: the fraction of full-time hours is the whole story, and the salary just follows it. Divide your weekly hours by the full-time week to get the fraction, then multiply. If your workplace treats 37.5 hours as full time and you do 30, that is 0.8, so a 30,000 full-time salary becomes 24,000. If full time is 40 hours and you do 16, that is 0.4. The one number that trips people up is the full-time week itself, because it is not fixed by law and varies by employer and country: 35, 37, 37.5 and 40 hours are all common, and the same personal hours give a different fraction against each. A 20-hour week is half of a 40-hour full week but well over half of a 35-hour one, so always use the full-time figure your own employer or the advert states rather than a round assumption. The calculator works in both directions, which is useful more often than it first appears. Read normally, it turns a full-time headline salary into your part-time pay. Read in reverse, by putting your own hours and salary in and raising the full-time hours to the standard week, it tells you the full-time-equivalent salary your pay implies, which is the number to quote when comparing your rate against full-time colleagues or against market pay surveys that are always stated full time. It is the honest basis for a like-for-like comparison, because two people on the same hourly worth can look very differently paid until you put both on a full-time footing. A few things sit outside this calculation and are worth keeping straight. Pro rata scales gross pay, not take-home, so income tax, national insurance or social contributions and any pension are worked out afterwards on the reduced salary, and because most tax systems are progressive a part-time worker often keeps a slightly higher percentage of a lower salary than the full-timer does. Pro rata also applies to more than salary: holiday entitlement, some bonuses, and benefits that accrue with time are commonly pro-rated on the same fraction, so the 0.6 that halves your pay also gives you 0.6 of the full holiday allowance. It is a different idea from a part-year calculation, where a full-time person starts or leaves partway through the year and is paid for the months worked rather than for reduced weekly hours; that is a fraction of the year, not a fraction of the week, though the arithmetic rhymes. And it is not the same as an hourly rate, though the two are linked: dividing the full-time salary by the full-time hours over a year gives an hourly figure that, multiplied back up by your hours, reaches the same place. Use this when weighing a part-time job advert, when moving from full time to reduced hours and needing the new figure for a budget, when checking that a payslip matches the hours agreed, or when a compressed or job-share arrangement changes the weekly total. Enter the salary as the full-time annual amount, set the full-time hours to whatever your workplace calls a full week, and put in your own hours to see the pay that proportion earns, before tax.

How it works

1. Enter the full-time annual salary, the figure a full-time person in the role is paid.
2. Set the full-time hours per week your workplace treats as a full week, commonly 35, 37.5 or 40.
3. Enter the hours you actually work in a week.
4. The calculator divides your hours by the full-time hours to get the proportion, then multiplies the salary by it.
5. It shows the pro-rata annual salary plus the monthly and weekly figures and the percentage of full time you are on.

Weekly hours employers commonly treat as full time

Key facts

• Pro rata is Latin for "in proportion": the salary follows the fraction of full-time hours worked.
• Job adverts quote the full-time salary even for part-time roles, so the real pay is lower than the headline.
• The full-time week is not fixed by law and varies by employer and country, changing the fraction.
• Pro rata scales gross pay; tax, contributions and pension are worked out on the reduced figure afterwards.

Tips

• Check the advert for the full-time week before assuming the salary; "pro rata" always means less than the headline for part-time hours.
• To compare your pay with full-time roles, convert to a full-time equivalent by setting the hours to a standard week.
• Remember holiday and some benefits are usually pro-rated on the same fraction, not just pay.
• For a part-year start rather than reduced weekly hours, scale by months worked instead of by hours.

Frequently asked questions

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