How this instrument works
UK take-home pay is gross salary minus two deductions that HMRC calculates by two different rules on the same payslip. Income Tax runs a rising ladder — 20% then 40% then 45% — while Class 1 National Insurance runs a shorter, falling one — 8% then 2%. Both start counting at the same £12,570 line, the personal allowance for tax and the primary threshold for NI, but from there the two systems diverge completely and are worked out independently before either touches the gross figure.
The instrument runs the two calculations side by side rather than blending them into one combined rate, because that is how PAYE actually operates: an employer's payroll software computes Income Tax and National Insurance as separate line items and subtracts both from gross pay before a wage lands in a bank account. A job seeker sizing up an offer letter, or an employee checking that a payslip matches what a raise should have produced, wants exactly that pair of numbers — not a single blended percentage that would hide which system moved and why.
What the sheet leaves out matters. It uses the 2024/25 rest-of-UK bands only — Scotland runs five income tax bands of its own with different thresholds and rates entirely. It does not taper the personal allowance away for income above £100,000, the mechanism that creates an effective marginal rate near 60% between £100,000 and £125,140 as £1 of allowance is withdrawn for every £2 earned. Pension contributions, student loan repayments, and the employer's own separate National Insurance bill are excluded too; each would change the true take-home figure a payslip prints.
- Enter your salary before any deduction into Gross annual income, £ — the figure on an offer letter or a payslip's gross line.
- Read Income tax, £/yr for the amount HMRC's three bands — 20%, 40%, 45% — take from that gross figure.
- Read National Insurance, £/yr for the separate Class 1 charge, which starts at the same £12,570 threshold but only has two bands, 8% then 2%.
- Read Take-home pay, £/yr for gross income minus both deductions — the annual figure that reaches a bank account before pension or student loan repayments.
- Push Gross annual income, £ past £50,270 or £125,140 to see Income tax climb and National Insurance's marginal rate fall at the very same thresholds.
Worked example — £40,000 gross salary
Set Gross annual income, £ to 40,000. That clears the £12,570 personal allowance and primary threshold, leaving £27,430 sitting inside both the 20% income tax band and the 8% National Insurance band — the same slice of income, taxed at two different rates by two separate systems. Income tax, £/yr comes to £5,486.00 and National Insurance, £/yr comes to £2,194.40.
Subtracting both from the gross figure gives Take-home pay, £/yr of exactly £32,319.60 — the case this instrument is built around. Raise the same input to £60,000 and the two systems split apart: the slice above £50,270 crosses into the 40% income tax band while that identical slice drops to just 2% National Insurance, producing £11,432.00 in tax and £3,210.60 in NI, for a take-home of £45,357.40.
Questions
Why does National Insurance fall to 2% at the same point Income Tax rises to 40%?
Because the two are different systems that happen to share the £50,270 threshold. National Insurance is a contribution scheme — money above the Upper Earnings Limit buys no extra State Pension entitlement, so its rate was set low at 2%. Income Tax is a general revenue tax with no such ceiling, so its rate keeps climbing at the very same line. The two moving in opposite directions at once is why a raise past £50,270 feels smaller than the headline 40% rate suggests.
Does this include the 60% tax trap between £100,000 and £125,140?
No. Above £100,000 the personal allowance itself is withdrawn — £1 of the £12,570 allowance for every £2 earned — until it disappears entirely at £125,140. That withdrawal is not modeled here, so this sheet understates Income tax, £/yr for any Gross annual income, £ inside that band; the true marginal rate there runs near 60%, not the 40% this instrument shows.
Does this work for a Scottish taxpayer?
No. Income Tax on non-savings income is devolved to Scotland, which runs five bands with different thresholds from the three rest-of-UK bands built into this instrument. National Insurance is unaffected by residency and uses the same UK-wide bands regardless, but Income tax, £/yr here reflects only the rest-of-UK schedule.
Why might my real payslip show different figures?
HMRC applies both thresholds per pay period — weekly or monthly — not once against a smoothed annual figure, so an uneven bonus month can land at a different rate than this annual model implies. A real payslip also nets out pension contributions before either tax is calculated and deducts student loan repayments afterward, neither of which this sheet includes.
Does this apply to a self-employed profit figure?
No. The self-employed pay Income Tax on the same three bands but owe Class 4 National Insurance instead of Class 1 — a different rate and threshold structure entirely, with no employer-side contribution ever charged. Enter only PAYE employment income run through an employer's payroll for this instrument's figures to hold.
Does Take-home pay, £/yr include what my employer pays?
No, and it should not. Employers pay a separate secondary Class 1 National Insurance charge on top of a salary, which never appears on a payslip and never reduces an employee's own take-home figure. Take-home pay, £/yr here reflects only the employee-side Income Tax and National Insurance already priced into the gross salary offered.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.