Your payslip arrives every month, the gross figure looks plausible, and most of us file it away without a second thought. But if you work part-time, that figure is the end product of a calculation — and calculations can be wrong. This guide shows you how to check pro rata pay on payslip documents in about ten minutes, and it is the single best way to make sure you are being paid exactly what your contract promises.
What your payslip should show
Before you check the maths, check the information. A proper UK payslip for a part-time salaried employee should show:
- Gross pay for the period (the figure before tax and National Insurance)
- Tax code and the tax deducted
- National Insurance deducted
- Pension contributions (yours, and often your employer’s)
- Hours worked, where your pay varies with the hours you do
- Year-to-date totals for pay and deductions
For salaried part-timers, the hours line sometimes just repeats your contracted hours each month. That is fine — but the gross pay figure is what you need to verify against your contract.
Step 1: Find your three contract numbers
Everything you need is in your employment contract or offer letter. Look for:
- The full-time equivalent (FTE) salary — e.g. “£28,000 per annum”
- Full-time hours — e.g. “37.5 hours per week”
- Your contracted hours — e.g. “22.5 hours per week”
Your contract may state your actual salary directly (“your salary will be £16,800 per annum”), in which case the check is trivial: does the payslip’s gross pay × 12 equal that figure? But many contracts state the FTE salary and your hours, leaving the pro-rata figure for you to derive. That is where errors creep in, and where this guide helps.
If any of the three numbers is missing from your paperwork, ask HR or payroll for it in writing. You cannot verify your pay without knowing what “full-time” means at your employer.
Step 2: Work out what you should be paid
The formula is:
Your salary = FTE salary × (your hours ÷ full-time hours)
Worked example: checking a monthly payslip
- FTE salary in contract: £28,000
- Full-time hours: 37.5 per week
- Your hours: 22.5 per week
- Your fraction: 22.5 ÷ 37.5 = 0.6
- Your annual salary: £28,000 × 0.6 = £16,800
- Your expected monthly gross: £16,800 ÷ 12 = £1,400
Now look at your payslip. If gross pay says £1,400.00, the calculation is correct. If it says £1,386 or £1,412, something is off — possibly a wrong hours baseline, a rounding choice, or an outdated FTE salary after a pay rise.
Quick-check table: monthly gross on common fractions (£28,000 FTE)
| Your hours (37.5h week) | FTE fraction | Annual salary | Monthly gross |
|---|---|---|---|
| 37.5 | 1.0 | £28,000 | £2,333.33 |
| 30 | 0.8 | £22,400 | £1,866.67 |
| 22.5 | 0.6 | £16,800 | £1,400.00 |
| 18.75 | 0.5 | £14,000 | £1,166.67 |
| 15 | 0.4 | £11,200 | £933.33 |
A few pounds of difference can come from rounding — payroll systems typically round to the penny at each step. But differences of tens of pounds or more deserve a question to payroll.
Step 3: Check the hourly rate underneath
Even as a salaried employee, you have an implied hourly rate, and it is worth calculating:
Hourly rate = annual salary ÷ (your weekly hours × 52)
Using the example above: £16,800 ÷ (22.5 × 52) = £16,800 ÷ 1,170 = £14.36 per hour.
Now compare that with the full-time hourly rate: £28,000 ÷ (37.5 × 52) = £28,000 ÷ 1,950 = £14.36 per hour. They match — which is exactly what the law requires. Part-time workers must not be paid a lower hourly rate than comparable full-timers without objective justification.
If your implied hourly rate is lower than the full-time equivalent, raise it. It usually means the wrong hours baseline was used in your calculation.
Step 4: Verify after changes — pay rises, new hours, new roles
Most pro-rata errors do not happen at the start of employment. They happen when something changes:
- A pay rise lands. Your FTE salary goes from £28,000 to £29,000. Your part-time salary should become £29,000 × 0.6 = £17,400, or £1,450 a month. Check the first payslip after the rise — payroll sometimes applies the increase late, or applies it to the wrong base figure.
- Your hours change. Moving from 22.5 to 30 hours a week changes your fraction from 0.6 to 0.8. The new monthly gross should be £28,000 × 0.8 ÷ 12 = £1,866.67. Mid-month changes should be split by days — check that both rates appear correctly.
- You move roles. A new role means a new FTE salary. Make sure payroll used the new role’s rate, not your old one.
After any change, keep that payslip and do the ten-minute check. Catching an error in month one means one correction; catching it in month eleven means eleven.
Red flags on a part-timer’s payslip
Watch for these warning signs:
- Gross pay that never changes after a announced pay rise. Either the rise has not been applied or it was applied to the wrong figure.
- A monthly figure that does not divide cleanly. £1,400 × 12 = £16,800 exactly. If your annualised payslip figure is £16,743.96, ask what baseline produced it.
- Holiday pay deductions you do not understand. For salaried part-timers, holiday is normally built into the annual salary. Extra deductions for bank holidays on non-working days are usually wrong.
- Overtime paid at the wrong rate. Overtime up to full-time hours is typically paid at your normal hourly rate; only hours beyond full-time usually attract a premium. Check which rate was applied.
If you want a second opinion on the maths before approaching payroll, run your three contract numbers through our free pro rata salary calculator — it takes seconds and gives you a figure to compare against your payslip.
What to do if the numbers do not add up
- Do the maths yourself first, using the method above, so you can state the exact discrepancy (“my payslip shows £1,386 but my contract implies £1,400”).
- Raise it with payroll in writing — email creates a record. Be polite and factual; most errors are genuine mistakes.
- Ask for a breakdown of how your figure was calculated: which FTE salary, which hours baseline, which fraction.
- Keep copies of your contract, the relevant payslips and the correspondence.
- Check back pay. If the error goes back months, you are owed arrears for the whole period.
- Escalate if needed. If payroll will not correct a clear error, speak to your union rep or ACAS. An unresolved underpayment can become an unlawful deduction from wages claim.
Employers are required to correct genuine payroll errors, and in our experience most are fixed within one or two pay cycles once flagged clearly.
FAQs
How do I check pro rata pay on my payslip if my contract only shows the FTE salary?
Use the three-number method: FTE salary × (your hours ÷ full-time hours) ÷ 12. That gives your expected monthly gross. Compare it with the gross pay line on your payslip.
My payslip gross is a few pence different from my calculation — is that a problem?
No. Payroll systems round to the penny at each calculation step, so differences of a few pence are normal. Differences of pounds, especially tens of pounds, are worth querying.
Should my payslip show my full-time equivalent salary?
Not necessarily — payslips show your actual pay, not the FTE figure. But your contract or offer letter should state the FTE salary and the full-time hours it relates to. If it does not, ask payroll to confirm both in writing.
What if my employer will not explain how my pro-rata figure was calculated?
You have the right to understand your pay. Ask in writing for a breakdown. If the employer refuses or the explanation does not add up, ACAS offers free, confidential advice, and a trade union rep can help you pursue it formally.
Ten minutes, once a month
You do not need to audit every payslip forever. Check the first payslip in a new job, the first payslip after any pay rise or hours change, and spot-check once or twice a year. That routine catches virtually every pro-rata error while it is still easy to fix.
And whenever you want an independent check on the numbers, the free pro rata salary calculator is there — enter your FTE salary and hours, and see in seconds what your payslip should say.
Keep a simple pay record of your own
You do not need a spreadsheet worthy of an accountant — a notes file on your phone is enough. Each time your pay changes, jot down the date, the FTE salary, the full-time hours, your hours, and the resulting monthly gross you expect. When the next payslip arrives, compare. This two-minute habit means you never have to reconstruct the maths from scratch months later, and if you ever do need to raise a query, you can show payroll exactly when the figures diverged. Employees who keep their own records resolve pay queries far faster than those relying on memory.