The £100k tax trap, with real numbers
Between £100,000 and £125,140 your personal allowance disappears at £1 for every £2 you earn — and the true marginal rate quietly becomes one of the highest in the system.
The worked example
Take a rise from £95,000 to £110,000 (no student loan, pension set aside for clarity). Gross, that is +£15,000 — and almost all of the damage lands on one payslip line.
On £95,000
full £12,570 personal allowance
On £110,000
allowance tapered to £7,570
£8,000 more income tax on £15,000 more pay. And it is concentrated: the slice from £100,000 to £110,000 alone keeps £3,800 of £10,000 — 38p per pound — because 40% tax combines with the personal allowance shrinking £1 for every £2 (an effective extra 20%) plus 2% NI. With a Plan 2 loan, the whole £15,000 rise keeps just 36%.
Why it happens
The personal allowance — £12,570 of tax-free income — tapers away above £100,000 of adjusted income and is gone at £125,140. Losing tax-free allowance while earning more means each pound in that band is taxed twice over: once directly at 40%, and once by converting allowance into taxable income. No published rate table says '60%' anywhere; it only emerges when you do the arithmetic, which is why the calculator computes it rather than quoting headline bands.
What people actually do about it
The classic response is salary-sacrificing the slice above £100,000 into pension — every sacrificed pound in the taper zone avoids the 60%+ marginal rate and lands whole in the pot (see salary sacrifice vs net pay and what a match is worth). Childcare-related cliff edges around £100k can push the effective rate higher still for parents — we deliberately do not model those, and say so on the methodology page.
If you are weighing an offer that crosses £100k, compare take-home, not salary — the gap between the two is nowhere larger than in this band. And remember that 38p in the pound is only the money axis: the roles that pay £110,000 usually reprice your hours, stress and security too, and a rise that thin buys very little tolerance for them. The calculator scores that side separately, so a taper-zone rise has to argue against what it actually costs you.
Run this scenario with your own numbers
The button opens the calculator pre-loaded with this exact worked example — change anything and every figure recomputes live, in your browser. Nothing you type is uploaded.