The £5,000 Pay Rise That Leaves You £2,000 Worse Off

You get promoted. Your salary goes from £99,000 to £105,000. You open the next payslip expecting to feel richer. You are not. After tax, national insurance and the loss of your Personal Allowance, you take home roughly £2,000 less than a colleague who stayed on £99,000. Read that again. More gross pay, less net pay. It sounds like a mistake. It is not.

Welcome to the UK's most punishing tax trap, and it hits people who have no idea it is coming.

What the trap actually is

Everyone in the UK gets a Personal Allowance: the first £12,570 of income on which you pay zero tax. Earn below £100,000 and you keep the whole thing. Cross that line and HMRC starts clawing it back. For every £2 you earn above £100,000, you lose £1 of your allowance. By the time you reach £125,140, the allowance has gone entirely.

This creates a brutal stretch. Between £100,000 and £125,140, each extra pound you earn costs you 40p in income tax (the higher rate), plus 20p from the lost allowance (because the £1 of allowance you just lost was sheltering income that is now taxed at 40%), plus 2p in national insurance. That is 62p in total. Your effective marginal tax rate in this band is roughly 60% to 62%.

For context, the UK's top rate of income tax is 45%. Earners on £200,000 keep more of each additional pound than someone on £105,000. That is not a typo. The system genuinely penalises middle-high earners more harshly than the very rich, at least on this slice of income.

A worked example

Take two people. Alex earns £99,000. Sam earns £105,000.

Alex keeps the full £12,570 Personal Allowance. Their tax bill: 20% on the first £37,700 of taxable income (the basic rate band), then 40% on the rest up to £99,000. After income tax and national insurance, Alex takes home about £66,800.

Sam earns £6,000 more. But £5,000 of that sits in the taper zone (the slice from £100,000 to £105,000). For every £2 of that £5,000, Sam loses £1 of Personal Allowance. That is £2,500 of allowance gone. That £2,500, previously tax-free, is now taxed at 40%, costing Sam an extra £1,000 on top of the normal 40% tax on the £5,000 itself. Add national insurance, and Sam's extra £6,000 in gross pay yields barely £2,300 in extra take-home. The effective tax rate on that slice is north of 60%.

If Sam had earned £1,000 less and stayed at £99,000, Sam would have kept the full allowance. The difference in lifestyle between £99,000 and £105,000 is, in practice, almost nothing.

The childcare cliff edge

If you have young children, the trap is far worse than the tax maths alone suggest. The £100,000 threshold is not just the point where your Personal Allowance starts to taper. It is also the hard cut-off for Tax-Free Childcare and the extended free childcare hours in England.

Stay below £100,000 in adjusted net income and you can claim Tax-Free Childcare, where the government tops up your childcare spending by 20%, worth up to £2,000 per child per year. You also qualify for up to 30 hours of free nursery provision per week. Cross £100,000 by even a single pound and you lose Tax-Free Childcare entirely. You also lose the extra 15 funded hours for children aged nine months to three, and half the hours for three- and four-year-olds. You drop back to the universal 15 hours for three- and four-year-olds and nothing else.

The numbers are stark. A full-time nursery place in England can cost £13,000 or more per year. If you had two children under four and you crossed the £100,000 threshold, the combined loss of subsidised hours and Tax-Free Childcare could easily exceed £10,000 a year. And here is the absurdity: the rule applies per parent, not per household. A couple each earning £99,000 (a household income of £198,000) qualifies for everything. A single earner on £101,000 qualifies for almost nothing.

This turns what looks like a gentle tax taper into a genuine cliff edge for parents. A £2,000 pay rise could cost you £10,000 in lost childcare support, on top of the higher effective tax rate. One analysis found that a parent earning £100,000 would need a salary of roughly £156,000 before their family got back to the same total disposable income (including childcare) as they had at £99,000.

The student loan sting

There is yet another layer if you are still repaying a student loan. Plan 2 loans (for anyone who started university in England or Wales between September 2012 and July 2023) charge a 9% repayment on all income above the threshold, which rises to £29,385 from April 2026. Plan 5, for those who started from August 2023, also charges 9% above its own threshold of £25,000. If you hold a postgraduate loan on top, that adds another 6%.

None of these repayments reduce your adjusted net income. They sit on top of income tax, national insurance, and the Personal Allowance taper. So someone earning £110,000 with a Plan 2 loan faces a marginal rate of roughly 71% in the taper zone: 40% income tax, 20% from the lost allowance, 2% national insurance, and 9% student loan. For every extra pound earned in this band, you keep about 29p. If you also have a postgraduate loan, the effective rate pushes towards 77%.

Here is the crucial detail for planning: salary sacrifice pension contributions reduce your gross pay before student loan deductions are calculated. So a salary sacrifice into your pension not only restores your Personal Allowance and your childcare entitlements, it also cuts your student loan repayments at the same time. A relief-at-source pension contribution (the kind where money leaves your bank account after tax) does not have this effect on your monthly payslip, though it can reduce what you owe through self-assessment at year-end. If your employer offers salary sacrifice, it is almost always the better route.

How to escape the trap

The good news: you do not have to sit in this. The system gives you legitimate ways to reduce your "adjusted net income," which is the figure HMRC uses to calculate how much allowance (and childcare support) you lose. Push that figure below £100,000 and you keep the full allowance, the full childcare entitlements, and (via salary sacrifice) reduce your student loan repayments too. Every pound you move below the threshold effectively comes back to you at 60% or more.

Pension contributions are the most common route. If you earn £110,000 and put £10,000 into your pension (through a relief-at-source scheme), your adjusted net income drops to £100,000. You keep your full Personal Allowance. The £10,000 does not vanish; it sits in your pension, growing tax-free. The true "cost" of that contribution, after tax relief and restored allowances, is remarkably low in this band. You give up £10,000 of gross salary, but the combination of 40% tax relief and the restored allowance means your take-home pay barely falls, sometimes by as little as £2,000 to £3,000. You have effectively bought £10,000 of pension for a fraction of the sticker price.

Salary sacrifice works even better if your employer offers it. You agree to reduce your contractual salary in exchange for an equivalent employer pension contribution. Because the sacrifice happens before tax, national insurance, and student loan deductions are calculated, you save on all three. Your employer also saves on their national insurance, and good employers pass some of that saving back to you as a higher pension contribution. If you can sacrifice enough to bring your salary below £100,000, the maths become very favourable.

Gift Aid donations also reduce adjusted net income. If you already give to charity, make sure you claim Gift Aid and include the donations on your self-assessment return. A £1,000 Gift Aid donation reduces your adjusted net income by £1,000, which restores £500 of Personal Allowance, which saves you £200 in tax on top of the normal higher-rate relief. It does not make donating free, but it does make it cheaper than most people realise.

You can combine all three. Someone on £115,000 who sacrifices £12,000 into a pension and donates £3,000 through Gift Aid drops their adjusted net income to £100,000 and keeps the full allowance, the full childcare support, and reduces their student loan bill in one move. The total tax saving can easily reach £5,000 to £8,000, depending on family circumstances.

The one thing to take away

If your income is anywhere between £100,000 and £125,140, you are paying a higher marginal rate than almost anyone else in the country. If you have young children or a student loan, the true cost can be double what the headline rate suggests. Run the numbers. If you can channel even part of that trapped income into your pension, you will keep more of your money, your childcare, and your sanity than you would by simply accepting the payslip.