How TruePay UK calculates your take-home pay

The order of the sums

Order matters in tax, because each step feeds the next. Our engine follows the same sequence HMRC does:

• Pension and salary sacrifice first. A salary-sacrifice pension reduces gross pay before anything else; a net-pay pension reduces taxable income but not National Insurance.
• Parse the tax code. The code sets your allowance (the number × 10), the region (S or C prefix), and any special handling — BR, K codes, W1/M1 and so on.
• Taper the allowance. Above £100,000, the personal allowance is reduced by £1 for every £2 of income.
• Apply the income tax bands for your region — the three England/Wales/NI bands or the six Scottish ones.
• Add National Insurance (8% then 2%) and any student loan.
• Subtract everything from gross to give take-home, then divide for monthly and weekly figures.

Where the rates come from

Every rate, threshold and band lives in a single configuration file, each entry tied to its gov.uk source. Nothing is hard-coded in a page. When a rate changes at the Budget, we update that one file and it flows through to every calculator, salary page and guide at once — which is why the £12,570 you see here matches the £12,570 everywhere else on the site. The full list is on our sources page.

How close we are to HMRC

We test our engine against a suite of reference cases and against HMRC’s own estimator. Our target is to match HMRC’s annual income tax and National Insurance figures to within £1. Small differences can arise from rounding conventions — HMRC rounds at each pay period, while an annual calculator works on yearly totals — but on the headline numbers we aim to be indistinguishable.

What we don’t handle

Being honest about the edges is part of being trustworthy. Our calculator assumes a single, steady source of PAYE income for the full year. It doesn’t model:

• Multiple jobs, or starting/leaving a job part-way through the year with real payslip history.
• Benefits in kind on the main calculator (though our car and EV calculators do handle them).
• Company directors’ NI, which uses an annual rather than per-period basis.
• Savings, dividend or rental income, which have their own rules.
• Scottish rate edge cases interacting with UK-wide savings tax.

For anything in that list, HMRC’s estimator or an accountant is the right tool — and we’ll say so rather than pretend otherwise.

Verification

Every rate below is being checked against its gov.uk source before launch; until that sign-off is complete, treat figures as provisional for the 2025/26 year.