A colleague of mine turned down a bonus once. Not a small one — enough to push her from £98,000 to £103,000 for the year. She’d done the maths and worked out that the extra £5,000 would actually leave her worse off than staying under £100,000. People assumed she was joking. She wasn’t.
That’s the thing about UK income tax — it isn’t just a set of bands you climb through. There’s a stretch of the system, right around six figures, that behaves nothing like the rest of it, and most people only find out when their payslip suddenly makes no sense.
**Where the taper bites**
Everyone gets a £12,570 personal allowance — the first slice of income that’s tax-free. Above £100,000, HMRC starts clawing that allowance back at £1 for every £2 you earn, until it disappears entirely at £125,140. Because you’re losing tax-free income at the same time as paying 40% on the earnings themselves, the effective rate on that stretch works out above 60%. Not 40%, not 45% — over 60p in every extra pound.
It’s the only part of the UK tax system where earning more can genuinely leave you keeping less of the next pound than you did a few pounds back, which is exactly the trap that had my colleague turning down her own bonus. The usual way round it is pension salary sacrifice — pushing income back under £100,000 so the allowance survives intact, which for a lot of higher earners is a far better return than the bonus itself would have been after tax. Running the actual figures through the [UK tax calculator](https://paychecktaxcalculator.net/calculator/uk) before accepting a bonus or negotiating a raise is a far safer bet than eyeballing it — the taper zone is exactly where back-of-envelope maths falls apart.
**National Insurance isn’t what it used to be**
Anyone comparing today’s payslip against an old one — or against an article from a couple of years back — will notice National Insurance looks different. The main employee rate was cut from 12% to 8% back in January 2024, and a lot of online calculators and old spreadsheets still haven’t caught up. It’s 8% on earnings between £12,570 and £50,270, then 2% above that. On a £52,000 salary, that works out to about £3,051 in NI for the year — noticeably less than it would have been under the old rate.
**Scotland runs its own numbers**
England, Wales, and Northern Ireland all use the same HMRC bands — 20%, 40%, 45%. Scotland doesn’t. Revenue Scotland sets its own six-band system: 19% starter, 20% basic, 21% intermediate, 42% higher, 45% advanced, and 48% at the top. National Insurance stays identical across the whole UK, so the entire difference between a Scottish payslip and an English one comes down to income tax.
At £52,000, that gap comes out to roughly £1,590 a year in Scotland’s favour of England — small at lower salaries, but it widens through the middle-income range where Scotland’s 21% and 42% bands start earlier than the equivalent English ones. Above £125,140, Scotland’s 48% top rate versus England’s 45% makes the gap wider still. What matters is where you live, not where your employer’s office is — a Scottish resident working remotely for a London company still pays Scottish rates.
**A concrete example**
Take a £52,000 salary in England, Wales, or Northern Ireland. Income tax works out to £8,232 — nothing on the first £12,570, 20% on the next £37,700, and 40% on the final £1,730. National Insurance adds £3,051. Take-home lands at £40,717, an effective deduction rate of about 21.7%, even though the top slice of that salary is taxed at 40%. That gap between the marginal rate and the effective rate trips people up constantly — being “in the 40% band” doesn’t mean 40% of the whole salary disappears.
**Worth checking before you sign anything**
Tax codes, workplace pension arrangements, and student loan plans all move these numbers around, sometimes by a lot. Salary sacrifice pensions save both tax and National Insurance, which makes them one of the more efficient ways to soften the £100,000 taper. Student loan Plan 2 and postgraduate loans stack, so someone with both can lose 15% of income above the combined thresholds on top of ordinary tax and NI. Whatever the situation, it’s worth seeing the real number rather than assuming a bonus or a move to Scotland will land the way it looks on paper.
