UK pay guide
How to calculate a pro-rata salary for part-time work
A pro-rata salary normally reflects the proportion of full-time contracted hours you will work. It is usually calculated before tax, pension and other payroll deductions.
The basic formula
Full-time annual salary × proposed weekly hours ÷ full-time weekly hours = pro-rata annual salary. For example, 30 hours compared with a 37.5-hour full-time week is 80% of the full-time salary.
Why take-home pay is not reduced by exactly the same percentage
Income Tax and National Insurance use thresholds and bands. Moving to part-time hours may move more of your income below a threshold, so the reduction in net pay can be smaller than the reduction in gross pay.
What to confirm with an employer
- The full-time contracted hours used for the comparison.
- Whether unpaid breaks count towards the stated weekly hours.
- How holiday, overtime, bonuses and benefits are handled.
- Whether pension contributions use full salary or qualifying earnings.
Pro-rata salary is not always the whole package
Some benefits are fixed, some are pro-rated and some depend on the role. Ask for the written offer and pension terms before comparing two roles only by headline salary.
Use the UK pro-rata salary calculator to estimate gross and take-home pay, then use the job-offer comparer for a broader package comparison. Income Tax and NI estimates use HMRC's 2026/27 rates and thresholds.