Pro-Rata Calculator: How to Work Out Part-Time Salary and Holiday Entitlement
Published: 14 March 2026
If you employ part-time staff or have someone joining mid-year, you need to calculate their pay and holiday entitlement proportionally. Getting this wrong can lead to underpayment, tribunal claims, and unhappy employees. This guide explains how pro-rata calculations work in the UK and shows you how to use our free pro-rata calculator to get accurate results instantly.
What Does Pro-Rata Mean?
Pro-rata is a Latin term meaning "in proportion." In UK employment, it is used whenever a worker is entitled to a proportional share of something that a full-time employee would receive in full. The three most common pro-rata calculations are:
- Pro-rata salary for part-time workers
- Pro-rata holiday entitlement based on working days per week
- Mid-year starter entitlement for employees who join part-way through the leave year
Our free calculator handles all three of these with separate tabs for each.
How to Calculate Pro-Rata Salary
The formula is straightforward:
Pro-rata salary = Full-time salary × (Actual hours / Full-time hours)
For example, if a full-time role pays £30,000 for 37.5 hours per week and an employee works 22.5 hours per week:
- £30,000 × (22.5 / 37.5) = £18,000 per year
- That works out to £1,500 per month, £346.15 per week, or £15.38 per hour
Under the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000, part-time workers must receive the same hourly rate as their full-time equivalents. If a full-time worker on £30,000 for 37.5 hours earns £15.38 per hour, the part-time worker must earn the same hourly rate.
How to Calculate Pro-Rata Holiday Entitlement
Under the Working Time Regulations 1998, all UK workers are entitled to 5.6 weeks of paid annual leave. For a full-time worker doing five days per week, that equals 28 days. Part-time staff receive the same 5.6 weeks, calculated proportionally:
Pro-rata holiday = Full-time entitlement × (Actual days / Full-time days)
Here are some common examples:
| Days per week | Holiday entitlement |
|---|---|
| 5 days (full-time) | 28.0 days |
| 4 days | 22.4 days |
| 3 days | 16.8 days |
| 2.5 days | 14.0 days |
| 2 days | 11.2 days |
For a deeper look at how this works with bank holidays, irregular hours, and common pitfalls, see our part-time holiday entitlement guide.
Mid-Year Starters
When someone joins part-way through the leave year, their holiday entitlement must be pro-rated based on the remaining portion of the year:
Starter entitlement = Full entitlement × (Remaining days / Total days in year)
For example, a worker starting on 1 July with a January-to-December leave year has 184 days remaining out of 365. Their entitlement would be 28 × (184 / 365) = 14.12 days. Most employers round this up to 14.5 or 15 days, as rounding down below the statutory minimum is not permitted.
The same principle applies to leavers. If someone leaves on 30 September, you calculate the proportion of the year they have worked and compare it against the leave they have already taken.
Common Mistakes to Avoid
- Rounding down. Pro-rata calculations often produce fractional results. You must never round down below the statutory minimum. Round up to the nearest half or whole day.
- Forgetting the 28-day cap. Statutory entitlement is capped at 28 days regardless of how many days someone works per week. A worker doing six days per week still only gets 28 statutory days, not 33.6.
- Confusing hours and days. If your business uses hours-based holiday tracking, make sure you convert correctly. A worker doing 22.5 hours across 3 days should have their holiday calculated in days (16.8) or hours (22.5 × 5.6 = 126 hours), not a mix of both.
- Ignoring bank holidays. If full-time staff get 28 days including bank holidays, part-time staff working fewer than 5 days may not work on all bank holiday days. You still owe them the proportional equivalent.
Try the Calculator
Our free pro-rata calculator handles all three calculation types in separate tabs. Enter your figures and get instant results with no sign-up required. It runs entirely in your browser and does not store any data.
Related Tools
- Free Pro-Rata Calculator - salary, holiday, and mid-year starter calculations
- Bradford Factor Calculator - measure absence impact
- Minimum Wage Checker - check current and historical NMW/NLW rates
Frequently Asked Questions
Pro-rata means proportional to time worked. If a full-time employee earns £30,000 for 5 days per week, a part-time employee working 3 days per week would earn £18,000 pro-rata (3/5 of £30,000). The same principle applies to holiday entitlement and other benefits.
Divide the full-time salary by the full-time hours, then multiply by the part-time hours. For example: £30,000 full-time salary / 37.5 hours = £800 per hour. £800 x 22.5 part-time hours = £18,000 pro-rata salary.
Multiply 5.6 weeks by the number of days worked per week. For example, someone working 3 days per week gets 16.8 days holiday (3 x 5.6). Part-time workers are entitled to the same proportion of leave as full-time workers.
Multiply the full annual entitlement by the fraction of the year remaining. For example, if someone starts on 1 July with a calendar-year leave year, they have 6 months (50%) remaining. A full-time entitlement of 28 days x 50% = 14 days for the remainder of the year.
In total days, yes. But proportionally, no. Both get 5.6 weeks. A full-time worker on 5 days per week gets 28 days. A part-time worker on 2 days per week gets 11.2 days. Both represent 5.6 weeks of their normal working pattern.