£100k Tax Trap Calculator 2025/26
If your income is between £100,000 and £125,140, you’re in the UK’s hidden tax trap — a 60% effective marginal rate created by the withdrawal of your personal allowance. This calculator shows exactly what you’re losing and how much pension contribution or Gift Aid is needed to escape.
Why you pay 60% tax between £100k and £125,140
HMRC tapers the personal allowance (£12,570) by £1 for every £2 of income above £100,000. This means the allowance reaches zero at £125,140. The problem: as each £2 of additional income is taxed at 40% and £1 of personal allowance is removed — taxing another £1 at 40% — the effective marginal rate becomes 40% + 20% = 60% on every pound earned between £100,000 and £125,140.
This means someone earning £125,140 pays exactly the same income tax as someone earning £125,141 or more — their personal allowance has been entirely withdrawn, and the 40% rate applies to the full additional rate band from there.
Pension contributions reduce your “adjusted net income” — the figure used to calculate the taper. A £10,000 pension contribution from someone earning £110,000 reduces ANI to £100,000, restoring the full personal allowance and saving up to £6,000 in tax. Gift Aid donations work similarly. Both must be made before 31 January following the tax year end to count.