Quick Answer
To calculate pro rata salary, divide the full-time annual salary by the full-time hours per week, then multiply by the actual hours worked. For a £28,800 salary based on a 36-hour week, an employee working 24 hours earns £19,200 pro rata. This is always a gross figure, tax and National Insurance apply separately.
What does pro rata mean?
Pro rata is a Latin phrase meaning "in proportion." In employment, it means a part-time employee receives a salary proportional to their hours compared to a full-time employee doing the same role.
If a full-time position pays £28,800 for a 36-hour week, someone working 24 hours is paid proportionally less. The calculation is straightforward, but it catches people out more often than you might expect.
Pro rata applies to salary, holiday entitlement, pension contributions, and most contractual benefits. Under the Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000, summarised in GOV.UK's part-time worker rights guidance, part-time workers in the UK have the right to the same hourly rate as their full-time equivalents. Pro rata pay is the legal standard for calculating this.
The pro rata formula
The calculation works in two steps. First you find the value per hour-week. Then you scale it to the actual hours worked.
Pro rata salary = (Full-time salary ÷ Full-time hours per week) × Actual hours per week
You do not need to convert anything to hourly rates first. The ratio of hours is what matters.
Worked example with real UK numbers
A full-time administrator role pays £28,800 a year based on a 36-hour week. A part-time candidate accepts the role at 24 hours per week.
Step 1: £28,800 ÷ 36 = £800 per "hour-week unit"
Step 2: £800 × 24 = £19,200 pro rata annual salary
| Value | |
|---|---|
| Full-time salary | £28,800 |
| Full-time hours per week | 36 |
| Actual hours per week | 24 |
| Pro rata salary | £19,200 |
The employee earns £19,200 gross per year. Income tax, National Insurance, and any pension contributions are then calculated on this £19,200 figure, not on the full-time equivalent.
You can check this instantly with our pro rata calculator.
How to calculate pro rata from an hourly rate
If you're quoted an hourly rate rather than a full-time salary, multiply your hourly rate by the hours you work per week, then by 52 weeks.
Example: £15 per hour × 25 hours × 52 weeks = £19,500 pro rata annual salary.
Pro rata for new starters joining mid-year
When someone joins part-way through the tax year, their salary is further adjusted for the proportion of the year remaining. A new starter joining on 1 October on £24,000 pro rata earns approximately £12,000 in their first year, six months of the annual salary.
Payroll software handles this automatically. Your first payslip will show the correct prorated monthly or weekly figure. Your P60 at year end will reflect only the earnings from your start date.
If you are negotiating a salary or checking your offer letter, always confirm whether the figure quoted is annual pro rata or the actual amount you will receive in year one.
Pro rata holiday entitlement
Part-time workers have the same statutory rights to paid holiday as full-time employees, it is just calculated pro rata. Under the Working Time Regulations 1998, the minimum is 5.6 weeks per year, as set out in GOV.UK's holiday entitlement guidance.
For a full-time employee working five days a week, that is 28 days.
- A worker doing 3 days a week gets 5.6 × 3 = 16.8 days, usually rounded up to 17
- A worker doing 4 days a week gets 5.6 × 4 = 22.4 days
The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 make it unlawful to treat a part-time worker less favourably than a comparable full-time worker. This covers not just salary but benefits, access to training, and career progression.
Our holiday pay calculator works out both entitlement in days and the monetary value of outstanding leave.
Is pro rata salary before or after tax?
Always before tax. The pro rata figure is a gross salary.
For 2026/27, the personal allowance is £12,570. On a £19,200 pro rata salary, you pay 20% basic rate income tax only on the portion above that threshold, £6,630 in this example. National Insurance contributions for employees are 8% on earnings between the primary threshold (£12,570) and the upper earnings limit (£50,270).
Your take-home pay will be noticeably less than the pro rata gross figure. For a precise net figure including all deductions, use our pro rata calculator, which applies the current 2026/27 rates.
Pro rata and salary sacrifice
If your contract includes a salary sacrifice arrangement, a pension contribution or an electric car scheme, for example, the sacrifice is typically calculated as a percentage of your pro rata salary, not the full-time equivalent.
Some employers base the sacrifice percentage on the full-time salary regardless of actual hours worked. Check your contract carefully. If the wording is ambiguous, ask your payroll team to confirm the basis for the calculation before you sign. Our guide to salary sacrifice explains how the sacrifice interacts with your tax and National Insurance once the reduced salary is in place.
Can my employer pay me less than minimum wage on a pro rata basis?
No. The National Living Wage for 2026/27 is £12.71 per hour for workers aged 21 and over, see the current figures on GOV.UK's National Minimum Wage rates page. Your pro rata salary must still result in an effective hourly rate at or above the applicable minimum wage rate for your age group, pro rating a salary never overrides the minimum wage floor.
The most common pro rata mistakes
The most frequent error is using the wrong "full-time" hours figure. If the job is advertised as 37.5 hours, use 37.5, even if you work a compressed four-day week or different shift patterns.
A second mistake is forgetting that employer pension contributions and some benefits are also adjusted pro rata. A 5% employer pension contribution on a £19,200 salary is £960 per year, not 5% of the full-time £28,800 equivalent.
If your employer is using 40 hours as the full-time baseline when the role is actually 37.5 hours, your pro rata salary will be calculated too low. Check the full-time hours in the job description or employee handbook.
Frequently asked questions
What is the pro rata salary for £32,000 working 20 hours out of 40?
Divide £32,000 by 40 to get £800, then multiply by 20. The pro rata salary is £16,000 gross per year.
Does pro rata just mean part-time?
Not exactly. Pro rata means proportional. It applies to any arrangement where an employee works fewer hours than the full-time equivalent for that role, including term-time only contracts, job share, and reduced-hours arrangements.
How is pro rata salary calculated for term-time workers?
For term-time only workers (common in schools), the calculation accounts for weeks actually worked. Divide the annual salary by 52 weeks, then multiply by the number of weeks actually worked per year. Holiday pay is typically rolled into the calculation.
Is holiday entitlement pro rata for part-time workers?
Yes. The statutory minimum of 28 days (5.6 weeks × 5 days) is scaled to the days worked each week. A three-day week gives 16.8 days entitlement, usually rounded up.
How is pro rata calculated for someone starting mid-year?
Take the annual pro rata salary, divide by 12, and multiply by the number of complete months from the start date to the end of the tax year. Payroll software does this automatically.
Is National Insurance calculated on a pro rata salary?
Yes. National Insurance is calculated on actual earnings above the primary threshold, regardless of whether the salary is pro rata or full time. For 2026/27, the threshold is £12,570 per year.
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