Why Salary Calculators Give Different Results

If you've tried more than one UK salary calculator, you've probably noticed they don't agree. It's usually not a bug. Different calculators make different assumptions about how your deductions work, and small differences in setup lead to different numbers.

Pension contribution method

The biggest source of disagreement is how pension contributions are handled. There are three methods, and each one produces a different take-home pay from the same gross salary:

Relief at source – The contribution comes out of your net pay. You pay tax on your full salary, and the pension provider claims 20% tax relief from HMRC on your behalf.
Net pay scheme – The contribution is deducted from your gross pay before income tax is calculated. You get full tax relief automatically, but NI is still charged on the original gross figure.
Salary sacrifice – You give up part of your salary before tax or NI is calculated. This usually produces the highest take-home pay of the three methods because you also save on NI.

Case study: £35,000 with a 5% pension

Assuming a £35,000 salary with £1,750 in pension contributions, the annual take-home pay would differ based on the three methods:

Relief at source: tax and NI are calculated on £35,000. The £1,750 pension is taken out of the net wage.
Net pay arrangement: tax is calculated on £33,250 (net of pension). NI is calculated on £35,000.
Salary sacrifice: tax is calculated on £33,250, similarly for NI.

If two calculators (where calculation includes pension) are showing different values, chances are they are using different methods. Ask your employer, check your payslip, or speak to HR to confirm which method applies.

Student loan repayment plan

The UK has five student loan plans, each with a different repayment threshold. Plan 5 starts at £25,000, Plan 1 at £26,065, Plan 2 at £28,470, Plan 4 at £32,745, and postgraduate at £21,000. The gap between the lowest and highest thresholds is over £11,000 a year.

Some calculators default to Plan 2 without making that obvious. If you're actually on Plan 1 or Plan 4, the take-home figure will be wrong. The Student Loans Company (SLC) can confirm which plan you're on.

Scotland vs rest of UK

Scotland has six income tax bands; the rest of the UK has three. Scottish rates run from 19% to 48%, while England, Wales, and Northern Ireland use 20%, 40%, and 45%.

A Scottish taxpayer pays approximately £7,852 income tax on a £50,000 salary, compared to £7,486 paid by workers in England on the same gross salary. That amounts to around £366 annually.

If a calculator does not ask which country you live in, it is probably using England/Wales rates by default. Scottish taxpayers should look for calculators that support Scottish tax codes (those beginning with “S”).

Rounding and timing conventions

HMRC rounds tax and NI to specific decimal places on each payroll run. Small rounding differences can accumulate over 12 months. A calculator that computes everything annually and then divides by 12 may produce a slightly different monthly figure than one that calculates each month individually.

When student loan thresholds are divided into monthly figures, rounding is done towards zero (divide the annual threshold by 12 and take any decimal down to the nearest pound). Not all calculators do this rounding, leading to a small variation in the total annual repayment amount.

How this calculator works

This calculator uses 2025/26 HMRC rates, supports English and Scottish tax codes, and covers all five student loan plans. Pension contributions are optional and calculated on qualifying earnings.

Thresholds are divided by 12 and rounded down to the nearest pound, following HMRC's method. The monthly figure is then multiplied by 12 for the annual total.

Salary sacrifice, benefits in kind, marriage allowance, and gift aid are not included. Full details are on the Salary Calculator Assumptions & Methodology page.