TL;DR
Pro rata salary is calculated by dividing the full-time equivalent annual salary by the standard full-time hours and multiplying by the hours you actually work. A 40,000 pound full-time salary on a 3-day week becomes 24,000 pounds. The same pro rata principle applies to annual leave, pension contributions and contractual benefits. Part-time workers have identical legal rights to full-time workers under the Part-Time Workers Regulations 2000.
Last reviewed: June 2026
Pro rata is a Latin term meaning proportional or in proportion. In UK employment, it is used to describe any pay, leave or benefit that is calculated as a proportion of the full-time equivalent, based on the fraction of full-time hours an employee actually works. It applies most commonly to part-time workers, but also to employees joining or leaving mid-year, those on reduced hours due to parental leave, and those working irregular patterns.
Understanding how your pro rata pay and benefits are calculated is essential for checking your payslip is correct and for comparing job offers that quote a full-time equivalent salary rather than an actual salary for the hours offered.
KEY FACTS
- Pro rata salary = (full-time salary / full-time hours per week) x actual hours per week.
- Statutory annual leave of 28 days (including bank holidays) is pro rated for part-time workers.
- The national minimum wage applies per hour and is not affected by pro rata arrangements.
- Auto-enrolment pension contributions are calculated on actual qualifying earnings, not the full-time equivalent.
- Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000 give part-time workers the same rights as comparable full-time colleagues.
- Bank holidays must be pro rated for part-time workers who do not work on the days those holidays fall.
How to calculate pro rata salary
The standard pro rata salary calculation divides the full-time equivalent (FTE) annual salary by the number of standard full-time hours per week, then multiplies by the number of hours the part-time employee actually works each week.
Formula: Pro rata salary = (FTE annual salary / FTE weekly hours) x actual weekly hours.
Example 1: A role advertised at 40,000 pounds FTE for a 37.5-hour week. A part-time employee working 22.5 hours (3 days) per week receives: (40,000 / 37.5) x 22.5 = 24,000 pounds per year.
Example 2: A role at 35,000 pounds FTE for a 40-hour week. An employee working 20 hours (2.5 days) per week receives: (35,000 / 40) x 20 = 17,500 pounds per year.
Where the standard full-time hours are not stated in a job advertisement, it is reasonable to ask before accepting a position. The most common full-time week in the UK is 37.5 hours, though some employers use 35 or 40 hours as their standard. The calculation must use the employer's stated full-time hours, not a general assumption.
Pro rata annual leave
Statutory annual leave entitlement under the Working Time Regulations 1998 is 5.6 weeks per year, which equates to 28 days for a worker on a standard 5-day week (including 8 bank holidays in England and Wales). For part-time workers, this entitlement is pro rated based on the number of days worked per week.
A worker on a 3-day week is entitled to 5.6 x 3 = 16.8 days of statutory annual leave per year, including their proportionate share of bank holidays. If the worker does not work on Mondays, for example, and most bank holidays fall on Mondays, their bank holiday entitlement in days will reflect the number of bank holidays that fall on their working days.
Many employers express annual leave in hours rather than days for part-time workers, which can make the comparison with full-time colleagues clearer. A 28-day full-time entitlement for a 7.5-hour day equals 210 hours. A 3-day-a-week worker on the same 7.5-hour days receives 16.8 x 7.5 = 126 hours.
Contractual annual leave (above the statutory minimum) must also be pro rated under the Part-Time Workers Regulations 2000. An employer who gives full-time staff 30 days per year must give a comparable part-time worker on a 3-day week 30 x (3/5) = 18 days.
Pro rata pension contributions
Under auto-enrolment, pension contributions are calculated on qualifying earnings: earnings between 6,240 pounds and 50,270 pounds per year (2026/27 thresholds). For part-time workers, qualifying earnings are based on their actual pay, not the FTE equivalent.
A part-time worker earning 24,000 pounds per year has qualifying earnings of 24,000 minus 6,240 = 17,760 pounds. The minimum total contribution of 8 percent applies to this amount: 1,421 pounds per year (employer minimum 3 percent = 533 pounds; employee minimum 5 percent = 888 pounds including tax relief).
The FTE salary is irrelevant for pension contribution calculations. Only actual earnings matter. Some employers choose to base contributions on total pay rather than qualifying earnings, which can produce higher actual contributions than the statutory minimum but the calculation still uses actual pay not FTE.
National minimum wage and pro rata
The national minimum wage (NMW) and national living wage (NLW) are set per hour and apply regardless of whether a contract is full-time, part-time or pro rata. For 2026/27, the NLW is 12.21 pounds per hour for workers aged 21 and over. Younger workers attract lower rates.
Pro rata arrangements cannot result in an effective hourly rate below the NMW or NLW. If a pro rata salary calculation produces a figure that, divided by hours worked, falls below the applicable minimum wage rate, the employer is in breach of the National Minimum Wage Act 1998 and the worker is entitled to the higher amount plus any arrears owed.
Workers who suspect they are being paid below the minimum wage can report this to HMRC, which enforces the NMW. HMRC can require employers to pay arrears and impose financial penalties. There is no qualifying period for NMW rights; they apply from the first hour of employment.
How to check your pro rata payslip
Your payslip must show your gross pay, any deductions (tax, national insurance, pension) and net pay. It should also show the period covered. To check your pro rata gross pay, divide your annual salary by 12 (for monthly pay) or by 52 (for weekly pay) and compare to the gross figure on your payslip.
Common pro rata payslip errors include using the FTE salary rather than the pro rata salary as the basis for calculations, incorrect annual leave accrual, failure to pro rate contractual bonuses or sick pay, and incorrect employer pension contribution calculations. If you identify a discrepancy, raise it with your employer's HR or payroll team in writing and request a written explanation.
Under the Employment Rights Act 1996, workers have a right to receive an itemised payslip and to request clarification of any item. Failure to provide adequate payslip information is a matter that can be referred to an employment tribunal.
Part-time rights under the Part-Time Workers Regulations 2000
The Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000 implement the EU Part-Time Work Directive and give part-time workers the right to the same contractual terms as a comparable full-time worker on a pro rata basis, unless the different treatment can be objectively justified.
This covers pay, contractual sick pay, maternity and parental leave rights, access to pension schemes, access to training and promotion opportunities, and protection from redundancy. A part-time worker who believes they are being treated less favourably than a comparable full-time worker can raise a grievance and, if unresolved, make a claim to an employment tribunal.
The right to request flexible working, extended to a day-one right from April 2024 under the Employment Relations (Flexible Working) Act 2023, allows employees to request a change to their working pattern including reduced hours. Employers must consider requests seriously and can only refuse on specific business grounds.
Frequently asked questions
How is pro rata salary calculated?
Divide the full-time equivalent annual salary by the standard full-time hours per week, then multiply by your actual weekly hours. For example, 40,000 pounds FTE for 37.5 hours becomes 24,000 pounds for a 22.5-hour (3-day) week.
Does pro rata affect my pension?
Yes, but based on actual pay not the FTE. Auto-enrolment contributions are calculated on qualifying earnings, which are your actual earnings between 6,240 pounds and 50,270 pounds. Your employer contributes at least 3 percent of your actual qualifying earnings.
Do part-time workers get the same annual leave?
Yes, on a pro rata basis. Statutory entitlement is 5.6 weeks per year regardless of hours. A worker on a 3-day week is entitled to 5.6 x 3 = 16.8 days including their proportionate share of bank holidays.
Can my employer pay me less per hour because I work part-time?
No. The Part-Time Workers Regulations 2000 prevent less favourable treatment compared to a comparable full-time worker unless objectively justified. The national minimum wage also applies per hour regardless of contract type. A lower hourly rate for part-time work is unlawful in most circumstances.
What if my pro rata payslip looks wrong?
Raise it in writing with HR or payroll, quoting the calculation you expect based on your contracted hours and FTE salary. If the employer cannot provide a satisfactory explanation, you can seek free advice from ACAS at acas.org.uk or raise a claim with an employment tribunal.
