UK Marginal Tax Rate Calculator
Combined marginal rate at every £1,000 of profit — income tax, Class 4 NI, student loans, HICBC, and the £100k trap.
Estimates only – not tax advice. For planning purposes only; does not replace professional advice or official HMRC calculations. Full disclaimer
Guidance, not advice. This calculator runs the rules as published, it doesn't assess your circumstances. Your actual tax may be affected by factors it doesn't cover (allowances used elsewhere, reliefs, marriage allowance, scheme-specific adjustments). Always seek financial or tax advice from your accountant, or contact HMRC. Read our editorial scope →
Assumptions
Combined marginal rate at every £1,000 of profit
- Combined
- Income tax
Shaded bands show known spike zones.
£100k personal allowance trap
62%£100,000 – £125,140
Personal allowance withdraws at £1 per £2 over £100k — pushing income tax to an effective 60%, plus 2% Class 4 NI and any student loan.
Spike zones explained
£100k–£125,140 PA taper: the personal allowance withdraws at £1 for every £2 over £100,000, producing a 60% income-tax marginal rate (with 2% Class 4) = 62%. In Scotland the trap is worse — closer to 67–69% combined.
HICBC zone (£60k–£80k): 1% of Child Benefit is lost per £200 over £60,000. The extra effective rate depends on the number of children. With two children the combined marginal rate exceeds 50%.
Student loan stacking: +9% (Plan 1/2/4/5) or +6% (Postgrad) on every pound above the relevant threshold. Plan 2 + Postgrad together = +15%.
Escape routes: pension contributions, Gift Aid, salary sacrifice and bringing-forward expenses can all push adjusted net income back below a cliff edge.
Walk-through of every band in our real tax rate guide.
Combined marginal rates are computed from headline UK rules for 2025/26 (income tax + Class 4 NI + student loan plans + HICBC) and exclude other tapers, allowances, and reliefs. Treat as a directional model, not a personal tax calculation.