data tool
Pro rata salary calculator
A pro rata salary is the full time salary multiplied by the part time hours over the full time hours. On £42,000 for 37.5 hours, a 22.5 hour job is 0.6 FTE and pays £25,200 a year. This calculator shows the FTE, the yearly, monthly and hourly pay, and what a mid year start earns to the end of the calendar year.
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How it works
- 1
Enter the full time salary
Type the salary for the full time version of the job.
- 2
Enter the hours
Type the full time hours a week and the part time hours a week.
- 3
Add a start date
If the job starts part way through the year, type the start date.
- 4
Read the result
The tiles show the FTE, the pro rata salary, the monthly figure and pay to 31 December.
The hours ratio
Pro rata means in proportion. A part time salary is the full time salary times the part time hours divided by the full time hours. On a 37.5 hour full time week, 30 hours is 0.8, 22.5 hours is 0.6 and 15 hours is 0.4. Applied to £42,000 those give £33,600, £25,200 and £16,800. The hourly rate does not change: £42,000 over 37.5 hours a week for 52 weeks is about £21.54 an hour whatever the hours.
FTE as a number on a job advert
Adverts often show a full time equivalent salary with an FTE figure, such as £42,000 FTE at 0.6, which means the job pays £25,200. Others show the pro rata figure, sometimes with the FTE in brackets. The FTE is the same hours ratio, so 0.6 FTE on a 37.5 hour week is 22.5 hours. Reading the advert as the actual pay when it is the FTE figure is the commonest mistake applicants make.
Table for 3, 4 and 4.5 day weeks
On a five day, 37.5 hour full time week, three days is 22.5 hours and 0.6 FTE; four days is 30 hours and 0.8 FTE; four and a half days is 33.75 hours and 0.9 FTE. On a £36,500 full time salary those pay £21,900, £29,200 and £32,850 a year, or £1,825, £2,433.33 and £2,737.50 a month. If the part time days are shorter or longer than the full time days, use the hours, not the days.
A mid year start, worked through
Someone starting on 7 September 2026 in a 30 hour role on a £36,500 full time salary is on 0.8 FTE, £29,200 a year and £2,433.33 a month. From 7 September to 31 December is 116 calendar days of 365, so they earn about £9,280 in 2026. A first payslip in September covers only part of a month, which payroll usually works out by working days in that month, so the first month can look a little different from the calendar day figure here. The yearly and monthly figures do not change.
Compressed hours are not pro rata
A worker who does 37.5 hours in four longer days instead of five is still full time and paid the full salary; the hours are rearranged, not reduced. Pro rata applies only when the total hours go down. The same goes for annualised hours, where the total over the year is fixed even though weekly hours vary. In both cases, type the total weekly hours averaged over the year into the part time field, and the calculator gives 1.0 FTE when they match the full time week.
Equal treatment for part time workers
Acas and gov.uk explain that part time workers should not be treated less favourably than comparable full time workers, so they should get the same hourly rate and the same benefits pro rata, such as holiday, sick pay and pension contributions. A part time job paid at a lower hourly rate than the full time role it mirrors is a warning sign, which is why the calculator shows that the hourly rate stays the same.
Putting it in the offer letter
An offer for a part time role should state the hours, the days if fixed, the FTE salary, the actual pro rata salary and how holiday is calculated. The AI document generator writes an offer letter from a description; give it the hours and the figures from this calculator so the letter states both salaries clearly.
Limits
- Gross pay before tax, National Insurance and pension.
- The hourly rate stays the same as full time; only the hours change.
- A mid year start is prorated by calendar days to 31 December; payroll may prorate by working days instead.
- Holiday entitlement is handled by the holiday pay calculator, not here.
What it does not do
- It does not work out take home pay.
- It does not apply minimum wage checks.
- It does not store the figures.
Questions people ask
How do I work out a pro rata salary?
Divide the part time hours by the full time hours and multiply the full time salary by the result. For 30 hours on a 37.5 hour week, that is 0.8, so a £36,500 salary becomes £29,200. Monthly pay is the yearly figure divided by 12.
What does 0.6 FTE mean?
It means the job is 60% of a full time job, so 0.6 times the full time hours and 0.6 times the full time salary. On a 37.5 hour week that is 22.5 hours, often three full days, and on a £42,000 salary it pays £25,200.
Is pro rata holiday included in a pro rata salary?
The salary covers paid holiday, but the amount of holiday is also pro rata: 5.6 weeks of the worker's own working week in the UK. Three days a week gives at least 16.8 days. The holiday pay calculator works that out.
How do I prorate a salary for a mid year start?
Multiply the yearly pro rata salary by the days from the start date to the year end, divided by the days in the year. Starting on 7 September on £29,200 gives about 116 days of 365, around £9,280. Payroll may count working days instead, which gives a slightly different figure.
Does pro rata change the hourly rate?
No. A part time worker should get the same hourly rate as a comparable full time worker. Pro rata changes the number of hours paid, and therefore the salary, but not the rate for each hour. The calculator shows that rate under the result.
What if full time hours differ between employers?
Use the full time hours of the employer offering the job, because the FTE is relative to their full time week. 30 hours is 0.8 FTE against 37.5 hours but 0.75 FTE against 40 hours, which changes the pro rata salary.
Write the offer letter
Take what you made here into documents.
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Background reading: the question page on this.
Sources
Written and checked by the OneCraft team. Last checked .