How to Work Out Pro Rata Salary

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Arianna Colomb Last updated: 26 February 2026 minute read

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Pro rata salary is a proportionate salary for part-time employees based on the number of hours worked compared to a full-time contract. It is calculated by dividing the full-time annual salary by the full-time hours and multiplying by the employee's actual contracted hours.

Paying your employees a salary can be a smart move for businesses because it eliminates some of the guesswork when dealing with wage calculations. But what if your employee doesn’t work the contracted amount of hours or days in their pay cycle? In this situation and a few others, it’s essential to know how to calculate their salary pro rata.

What is pro rata salary?

Pro rata is a Latin term meaning "in proportion." A pro rata salary is the amount an employer pays a part-time worker based on what they would earn if they worked full-time.

For example, if a full-time role pays £40,000 for 40 hours a week, an employee working 20 hours (exactly half) would receive a pro rata salary of £20,000. This ensures fair compensation based on actual time worked.

How to calculate pro rata salary for part-time staff

To work out a pro rata salary, you need to find the "Full-Time Equivalent" (FTE) and then adjust it to the employee's specific hours.

The simplest way to perform a pro rata calculation is using the following formula.

(Annual Salary : Full Time Hours) x Actual Working Hours = Pro Rata Salary

Pro rata salary calculation example

In these scenarios, we use a 40-hour full-time baseline for the annual salary.

For the mid-month start we can substitute “full time hours” with “full time days” and “actual working hours” with “actual working days”.

Scenario	Annual salary	Calculation	Pro rata result
Half-time (20 hrs/wk)	£30,000	(£30,000 : 40) x 20	£15,000
3 days (24 hrs/wk)	£35,000	(£35,000 : 40) x 24	£21,000
Mid-month start	£24,000 (£2,000/mo)	(£2,000 : 20 working days) x 10	£1,000

Calculating pro rata holiday entitlement

Just like salary, holiday leave must be adjusted for part-time staff. By law, most workers are entitled to 5.6 weeks of paid holiday per year (that’s 28 days including bank holidays).

To find pro rata holiday entitlement, use this simple formula:

Days Worked per Week x 5.6 = Annual Holiday Entitlement (Days)

Examples of pro rata leave:

Working 4 days a week: 4 x 5.6 = 22.4 days
Working 3 days a week: 3 x 5.6 = 16.8 days
Working 2 days a week: 2 x 5.6 = 11.2 days

HMRC rules state you cannot round down holiday entitlement. A result like 22.4 days would either be 22.5 days or 23 days—it cannot be rounded down to 22. For employees with irregular hours or those who start mid-year, you can use the official GOV.UK holiday calculator to double-check your math.

How pro rata salary affects benefits

According to the Part-Time Workers Regulations, part-time employees are entitled to the same benefits as full-time employees on a pro rata basis. You cannot treat them "less favourably" just because they work fewer hours.

Bonuses: If a full-time employee receives a £1,000 bonus, a part-time employee working 50% of the hours should receive £500.
Pensions: Employers must still pay into a pension if the employee meets the auto-enrolment criteria. The contribution is based on their actual pro rata earnings.
Health & Perks: For non-monetary benefits like gym memberships or private health insurance, you should provide the benefit or its cash equivalent pro rata where possible.

Is hiring part-time right for your business?

Building a team is a major step. Deciding between part-time and full-time staff depends on your budget and how much work you have available.

The advantages

Lower fixed costs: You only pay for the specific hours you need. In 2026, with the National Living Wage at £12.71 (for ages 21+), keeping a lean workforce helps you stay agile.
Flexibility for peak times: Part-time staff are perfect for covering busy lunch rushes, weekend shifts, or seasonal peaks (like Christmas) without the commitment of a 40-hour contract.
Access to specialised senior talent: Many experienced professionals (parents, semi-retirees, or "portfolio" workers) prefer part-time roles. This allows you to hire a "pro" for two days a week that you might not be able to afford full-time.
Higher productivity: Studies often show that part-time workers can be more productive per hour because they stay focused during shorter shifts and suffer less "burnout" than full-time staff.

The disadvantages

Increased admin & legal duties: In 2026, even part-time and casual workers have "Day One" rights to Statutory Sick Pay (SSP) and Paternity Leave. Managing these pro rata calculations across multiple staff requires extra attention.
Communication gaps: If a staff member only works Tuesday and Thursday, they may miss Monday’s team meeting or Friday’s client update, which can slow down projects.
Training & onboarding costs: It takes just as much time to train a part-time employee on your systems as it does a full-timer. You are essentially paying for 100% of the training for 50% of the output.
Higher turnover: Part-time workers may view the role as supplemental and be more likely to "jump ship" if they find a full-time position or a better-paying gig elsewhere.

Legal rights for part-time vs full-time employees

Under the Part-Time Workers Regulations, it is illegal to treat part-time staff less favourably than full-time staff. They must receive the "same treatment" adjusted for their hours.

Equal Hourly Pay: They must receive the same hourly rate as a full-time colleague in the same role.
Pro Rata Benefits: They are entitled to the same benefits (like bonuses or health insurance) on a proportionate basis.
Bank Holidays: Part-time staff are entitled to a pro rata share of bank holidays, even if their working days don't fall on a Monday.

For a full picture of the rules, you can visit the Part-time workers' rights page on GOV.UK.

The bottom line

Calculating pro rata salary ensures your team is paid fairly and keeps your business compliant. While it involves a bit of extra admin, it allows you to scale your business flexibly without the immediate cost of a full-time hire. By creating a workplace built on fairness and trust, you can manage equitable wages regardless of working hours.

Managing payroll for part-time staff is easier when your expenses are organised. The Capital on Tap Business Credit Card allows you to integrate with accounting software like Xero or QuickBooks, so you can track all your business costs and staff expenses in one place.