Often, the only number you are ever given is an annual salary. The job advert says £38,000. Your offer letter says £38,000. Your contract says the role “carries a salary of £38,000 per annum, payable pro rata”. But you are not working full time — so what does that one yearly figure actually mean for your bank account each month, each week, and each hour?
A pro rata salary calculator with annual salary starts from exactly that single figure and converts it, step by step, into every amount you actually live on: your part-time annual salary, your monthly payslip figure, your weekly equivalent and your true hourly rate. This guide shows the full conversion chain, with worked examples and a table covering the most common UK annual salaries, so you can do it for any annual figure you are quoted.
What you need before you start
The annual salary alone is not quite enough. To scale it down fairly you also need the shape of the full-time week it was quoted for, because “full time” is not the same everywhere:
- The annual salary — the full-time figure from the advert, offer letter or contract.
- The full-time weekly hours — commonly 37.5, but 35, 39 and 40 are all widespread. This is the number people most often get wrong.
- Your weekly hours (or days) — what you will actually work.
With those three numbers, every other figure follows by simple division and multiplication. Miss the second one, and two employers quoting the same £38,000 could mean noticeably different part-time pay.
Step by step: from annual salary to part-time pay
Step 1: Find the hourly rate hidden inside the annual salary
An annual salary is really an hourly rate wearing a disguise. Strip it back:
Hourly rate = annual salary ÷ full-time weekly hours ÷ 52
For a £38,000 salary on a 37.5-hour week: £38,000 ÷ 37.5 ÷ 52 = £19.49 an hour (rounded). This rate is the anchor for everything else. It does not change when your hours change — it is the rate for the job, full stop.
Step 2: Scale the annual salary by your fraction
Your fraction (your FTE) is your hours divided by the full-time hours. Working 22.5 hours against a 37.5-hour week gives 22.5 ÷ 37.5 = 0.6 FTE. Now scale the annual figure:
Your annual salary = full-time annual salary × your FTE
£38,000 × 0.6 = £22,800 a year.
Step 3: Convert your annual salary into monthly and weekly pay
Salaried staff are normally paid monthly, in equal instalments:
Monthly pay = your annual salary ÷ 12 → £22,800 ÷ 12 = £1,900 a month (gross)
Weekly pay = your annual salary ÷ 52 → £22,800 ÷ 52 = £438.46 a week (gross)
Note that monthly pay is not weekly pay multiplied by four — there are 4.33 weeks in an average month, which is why the annual ÷ 12 route is the only reliable one.
Step 4: Sense-check using the hourly rate
Multiply your hourly rate by your weekly hours: £19.49 × 22.5 = £438.46 a week — the same weekly figure as Step 3. If the two routes disagree, an input is wrong, most often the full-time hours. This thirty-second check is worth doing every single time.
A full worked example: £42,000 annual salary, three patterns
Say the annual salary on the contract is £42,000, quoted for a 37.5-hour week, and the hourly rate works out at £42,000 ÷ 37.5 ÷ 52 = £21.54. Here is what that one figure becomes under three common part-time patterns:
| Pattern | FTE | Your annual salary | Monthly | Weekly | Hourly rate |
|---|---|---|---|---|---|
| 3 days a week (22.5 hrs) | 0.6 | £25,200 | £2,100 | £484.62 | £21.54 |
| 4 days a week (30 hrs) | 0.8 | £33,600 | £2,800 | £646.15 | £21.54 |
| 18.75 hours a week | 0.5 | £21,000 | £1,750 | £403.85 | £21.54 |
Look at the last column. Whatever pattern you choose, the hourly rate stays pinned at £21.54 — because it is derived from the annual salary and the full-time week, and neither of those changes when your hours do. If a part-time offer based on a £42,000 full-time salary implies a lower hourly rate, the annual figure has been reduced twice, and you should query it before signing.
Common annual salaries at 0.5, 0.6 and 0.8 FTE
The table below takes the annual salaries most often seen in UK job adverts and shows the part-time annual and monthly pay at the three most common fractions. It assumes the fraction applies directly to the salary (the hours question matters for the hourly rate, not for these figures), so you can use it whatever your employer’s standard week is.
| Full-time annual salary | 0.5 FTE annual | 0.5 FTE monthly | 0.6 FTE annual | 0.6 FTE monthly | 0.8 FTE annual | 0.8 FTE monthly |
|---|---|---|---|---|---|---|
| £25,000 | £12,500 | £1,041.67 | £15,000 | £1,250 | £20,000 | £1,666.67 |
| £30,000 | £15,000 | £1,250 | £18,000 | £1,500 | £24,000 | £2,000 |
| £35,000 | £17,500 | £1,458.33 | £21,000 | £1,750 | £28,000 | £2,333.33 |
| £40,000 | £20,000 | £1,666.67 | £24,000 | £2,000 | £32,000 | £2,666.67 |
| £45,000 | £22,500 | £1,875 | £27,000 | £2,250 | £36,000 | £3,000 |
| £50,000 | £25,000 | £2,083.33 | £30,000 | £2,500 | £40,000 | £3,333.33 |
Two useful things fall out of this table. First, monthly pay rises in a straight line with the fraction — there are no hidden steps or thresholds in the gross salary itself. Second, the jump from 0.6 to 0.8 FTE on £35,000 is £583.33 a month gross, which is the sort of concrete figure that makes a conversation about changing your hours much easier to have.
When only the annual figure is on the contract
Many contracts state one annual salary and the words “pro rata” — and nothing else. That leaves several practical questions open, and the answers depend on details worth nailing down in writing before you start:
- Which annual figure governs if the full-time salary rises? If the full-time role gets a pay award, your pro rata amount should rise by the same percentage automatically, because it is a fraction of that figure. Confirm your contract links the two, rather than freezing your own number at the starting amount.
- What counts as full time? If the contract never defines the full-time week, get it confirmed by email. A role recalculated from a 40-hour assumption to a 37.5-hour reality keeps the same annual pro rata total but changes your hourly rate — which matters for overtime, enhancements and hourly-paid extras.
- Is your own annual amount also stated? The clearest contracts give both: the FTE salary and your actual pro rata annual salary. If yours only gives the FTE figure, do the conversion yourself using the steps above and keep a copy of your working. It is your evidence if payroll ever uses a different fraction.
- How are mid-year starters handled? If you join part-way through the year, you simply receive monthly instalments of your pro rata annual salary — the annual figure does not shrink further because you started late. Each full month pays annual ÷ 12; a part-month at the start is usually worked out on days or hours actually worked.
A final trap: job adverts sometimes quote “£28,000 pro rata” when £28,000 is actually the amount paid for the part-time hours on offer, not the FTE figure. The two readings differ enormously. If the wording is ambiguous, ask one direct question — “Is that the full-time equivalent, or the actual salary for the hours advertised?” — before you do any maths at all.
Skip the arithmetic
The conversion chain above is simple, but it has four steps and three inputs, and it only takes one wrong input — a 40-hour assumption on a 37.5-hour contract — to throw every figure out. The free pro rata salary calculator on our homepage takes just the annual salary and the hours, and returns the part-time annual, monthly, weekly and hourly amounts in one go, so you can sanity-check an offer letter or a payslip in seconds rather than reaching for a spreadsheet.
Common mistakes when working from an annual salary
- Dividing by the wrong full-time hours. The single biggest source of error. A £38,000 salary implies £19.49 an hour on a 37.5-hour week but £18.27 on a 40-hour week. Always use your employer’s actual full-time hours.
- Turning monthly pay into weekly pay with × 4. A month is not four weeks. Weekly = annual ÷ 52, monthly = annual ÷ 12. Mixing the two understates weekly pay by roughly 8%.
- Rounding the fraction too early. Using 0.67 instead of 25 ÷ 37.5 (0.6667) on a £40,000 salary creates a difference of about £133 a year. Keep full precision until the final figure, then round.
- Treating the annual figure as take-home pay. Everything in this guide is gross. Tax and National Insurance depend on your total income and tax code; as a rough orientation, a £22,800 gross salary loses far less to deductions than a £38,000 one, so the gap between full-time and part-time take-home pay is smaller than the gap between the gross figures.
- Forgetting allowances that do not scale. Some payments — a fixed first-aider allowance, an on-call retainer — may be paid flat rather than pro rata, or the other way round. Check the wording for each element of the package separately.
Frequently asked questions
How do I turn an annual salary into an hourly rate?
Divide the annual salary by the full-time weekly hours, then by 52. For example, £33,000 on a 37.5-hour week: £33,000 ÷ 37.5 ÷ 52 = £16.92 an hour. This is the rate the job pays regardless of how many hours you personally work.
If my contract only states an annual salary, is that what I will be paid?
Only if you work full time. If you work part time, that annual figure is the full-time equivalent and you will be paid your fraction of it. Your own annual amount should be the quoted salary multiplied by your FTE — for example, £33,000 × 0.6 = £19,800, paid as £1,650 a month.
Why does my monthly pay stay the same in February?
Because salaried pay is the annual amount divided into twelve equal instalments, regardless of how many working days a particular month contains. Your annual salary is spread evenly across the year, which is also why a month with five pay-affecting weekends does not change a salaried payslip.
What if my annual salary changes mid-year?
Your remaining monthly instalments are recalculated from the new annual figure, and the month of the change itself is usually split between the old and new rates. Check that payslip twice: once for the new fraction or salary being right, and once for the split falling on the correct date.
From one number to the full picture
An annual salary on its own tells you surprisingly little — it is the starting point, not the answer. Run it through the chain in this guide (hourly rate, fraction, annual, monthly, weekly) and that single contract figure becomes the numbers you actually budget with. And when you want those numbers without the long division, the pro rata salary calculator with annual salary approach on our homepage does the whole conversion instantly: annual salary in, every part-time figure out.