Reviewed for UK readers: September 2026.
When you move from full-time to part-time work, your gross salary can be calculated directly from the working fraction, but your net pay usually does not change in exactly the same proportion. First find the gross amount with our pro rata salary calculator UK; then estimate PAYE and other deductions on that new annual salary.
This distinction is important when deciding whether a reduced-hours role is affordable: “80% of salary” does not automatically mean “80% of take-home pay”.
Quick answer
- Gross salary changes directly with the FTE ratio.
- Income Tax is banded, so tax may fall by a different percentage.
- National Insurance, pension and student loans also matter.
- Scottish employment-income tax bands differ from the rest of the UK.
Gross versus net pay
Gross pay is the contractual amount before payroll deductions. Net or take-home pay is what remains after PAYE Income Tax, employee National Insurance, pension contributions and any other deductions.
Why take-home pay is not linear
If gross salary falls from £50,000 to £30,000, part of the previous income may have been taxed at a higher marginal rate. The lower salary therefore loses less tax than a simple 40% scaling would suggest.
2026/27 tax context
The standard Personal Allowance for 2026/27 is £12,570 where available. England, Wales and Northern Ireland use the main rates, while Scotland has separate employment-income bands and rates. Use the correct jurisdiction and tax year when estimating net pay.
Other deductions
Workplace pension contributions can be based on qualifying earnings, pensionable pay or another scheme-specific definition. Student and postgraduate loan deductions also have their own thresholds. Salary sacrifice can reduce taxable or NIC-able pay depending on the arrangement.
A practical decision method
Compare three numbers: current monthly net pay, expected monthly net pay at the new FTE, and the value of the additional non-working time. Also check whether reduced hours affect employer pension contributions, bonuses or other benefits.
What a pro rata tax estimate cannot know
A general calculator cannot see your live tax code, earlier pay in the tax year, benefits, second jobs, pension method, student loans or HMRC adjustments. Use a pro rata calculation to establish gross salary, then treat any take-home figure as an estimate until it is confirmed by payroll or HMRC.
If your circumstances are unusual, use current HMRC information rather than relying on an old tax table. Rates and thresholds can change between tax years.
Use the calculator
For a quick gross salary estimate, use the Pro Rata Calculator UK. Enter the full-time salary and your hours, days or FTE, then compare the result with your contract or payroll figure.
Frequently asked questions
Will my take-home pay be exactly 80% if I work 0.8 FTE?
Usually not. Gross basic salary may be 80%, but tax and other deductions do not necessarily scale linearly.
Does pro rata salary include pension deductions?
No. Pro rata salary normally means gross contractual pay before pension and payroll deductions.
Why is my calculator result different from my payslip?
Tax code, pension, student loans, benefits, overtime and payroll timing can all create differences.
Should I calculate gross or net pay first?
Calculate gross pro rata salary first, then apply the correct tax and deduction assumptions.
Authoritative sources
This article is general information, not personalised legal, tax or payroll advice. Employment contracts, collective agreements and individual circumstances can change the correct result.