Quick Answer
To calculate pro rata salary based on days worked, use this formula: (annual full-time salary ÷ 260) × days you work each week — or more precisely, annual salary × (your weekly days ÷ 5). A £30,000 full-time salary for someone working 2 days a week gives £30,000 × 0.4 = £12,000 a year, or £1,000 a month before tax. The rest of this guide explains when to use the days method, how to handle uneven weeks, and how to check your payslip.
How the Days-Worked Method Works
The days-worked method is the simplest way to pro-rate a salary: you take the full-time annual salary and multiply it by the fraction of the working week you actually do. In the UK, a standard full-time week is 5 days, so the fractions are refreshingly simple — 1 day is 0.2, 2 days is 0.4, 3 days is 0.6, and 4 days is 0.8 of full-time pay.
This is the method most UK employers reach for first when someone works fixed whole days. It appears on offer letters as “pro rata of £X” and it is what payroll software applies when your contract says “2 days per week”. Because it is so standard, it is also the method tribunals expect to see for straightforward part-time arrangements.
The Formula, Step by Step
- Find the full-time equivalent (FTE) salary. This is the advertised annual salary for the full-time version of the role — say £30,000.
- Divide your days by 5. Working 2 days a week? That’s 2 ÷ 5 = 0.4, i.e. 40% of full-time.
- Multiply. £30,000 × 0.4 = £12,000 gross per year.
- Convert to monthly or weekly if you like. £12,000 ÷ 12 = £1,000 per month; £12,000 ÷ 52 = £230.77 per week.
That’s the whole calculation. The worked example below shows it in a table for the most common UK patterns.
Worked Example: £30,000 Full-Time Salary
| Days per week | Fraction of FTE | Annual pro rata salary | Monthly (gross) | Weekly (gross) |
|---|---|---|---|---|
| 1 day | 0.2 | £6,000 | £500.00 | £115.38 |
| 2 days | 0.4 | £12,000 | £1,000.00 | £230.77 |
| 3 days | 0.6 | £18,000 | £1,500.00 | £346.15 |
| 4 days | 0.8 | £24,000 | £2,000.00 | £461.54 |
| 5 days | 1.0 | £30,000 | £2,500.00 | £576.92 |
Monthly figures are the annual salary divided by 12 — which is how UK payroll actually pays you. Weekly figures divide by 52.
When Days Worked Is the Right Method
Use the days-worked method when your contract specifies whole days: “3 days per week”, “0.6 FTE”, or named days like “Monday to Wednesday”. It is the cleanest fit, the easiest to check on a payslip, and the one your employer’s payroll is most likely using.
It also makes comparisons easy. Two job offers — one at £28,000 for 3 days, another at £32,000 for 4 days — can be compared instantly by converting both to their full-time equivalent: £28,000 ÷ 0.6 = £46,667 FTE versus £32,000 ÷ 0.8 = £40,000 FTE. The first offer pays the better rate, even though the headline salary is lower.
When to Calculate by Hours Instead
The days method assumes every working day is the same length. If yours aren’t — say you work Monday 9–5 but Friday 9–1 — the hours method is fairer and usually what the law expects for working-time calculations. A 4-day week of short days can be fewer hours than a 3-day week of long ones.
The hours formula is the same shape: annual salary × (your weekly hours ÷ full-time weekly hours). Someone on £30,000 FTE working 15 hours against a 37.5-hour full-time week gets £30,000 × 0.4 = £12,000 — the same answer as 2 equal days, but reached honestly.
Uneven Weeks and Rotas
Not everyone works the same days each week. If you work a rotating pattern — 3 days one week, 4 the next — average it: 3.5 days a week is 0.7 FTE. Over a fortnight that’s 7 days out of 10, and payroll will typically apply the averaged fraction across the year.
For genuinely irregular hours with no pattern, UK employers often fall back on the 12.07% method for holiday pay, but basic salary pro-rating still uses your contracted average. If your contract states an average, that average is what your salary is based on — keep a copy of it.
Checking Your Payslip
Take your gross monthly pay from your payslip and multiply by 12, then compare it with the annual figure your contract promises. Small rounding differences of a pound or two are normal — payroll systems round at different stages. A gap bigger than that deserves a question to payroll, armed with the formula above.
Also check which day-count your employer uses. Most UK payrolls treat the year as 260 working days (52 × 5), but some use 261 or 262 to account for the exact calendar. Over a year the difference is tiny, but it explains why two calculators can disagree by a few pounds.
Common Mistakes With the Days Method
- Confusing days with FTE. “0.6” means 3 days, not 3.5 — always divide days by 5.
- Forgetting bank holidays. Part-time staff get a pro-rata share of bank holidays; if you work Mondays, most bank holidays fall on your working day and your entitlement calculation should reflect that.
- Using calendar days. Pro rata salary uses working days (260-ish a year), not 365. Dividing by 365 understates your pay.
- Ignoring unpaid leave. A week of unpaid leave reduces the year’s pay by roughly 1/52 — check it was deducted once, not twice.
Other date-based calculations: joining mid-month · leaving mid-month · partial month · start and end dates · daily rate · starting mid-year · notice pay · redundancy pay
Use the Calculator
Want your exact figure without the arithmetic? Our free pro rata salary calculator handles days, hours, and FTE — enter your full-time salary and working pattern and it does the rest, with a full breakdown.