The £100k Salary Trap: How to Protect Your Personal Allowance

A pay rise that leaves you worse off sounds like a mathematical impossibility. In the UK tax system, it isn't. If your income crosses £100,000, you enter one of the most punishing tax traps in the developed world — a zone where you keep just 40p of every extra £1 you earn, while also losing pension credit, child benefit entitlements, and other means-tested benefits.

This article explains exactly how the trap works, who it catches, and — most importantly — how to escape it.

What Is the Personal Allowance Taper?

The Personal Allowance is the amount of income you can receive before paying any income tax. For 2024/25 it is £12,570.

However, above a certain income level, HMRC starts taking this allowance away. The rules are:

• For every £2 of adjusted net income above £100,000, you lose £1 of Personal Allowance.
• At £125,140, your Personal Allowance has been reduced to zero.
• Between £100,000 and £125,140, you are in the taper zone.

The mathematics of this is what creates the 60% effective rate.

The Maths: Why the Effective Rate Is 60%

Here is the step-by-step calculation for an extra £1 of income when you are already earning £100,000:

1. Income tax at 40%: You pay 40p in income tax on that extra £1.
2. Lost Personal Allowance (£0.50): Every extra £2 of income loses £1 of Personal Allowance. So the extra £1 of income costs you £0.50 of Personal Allowance.
3. Tax on the lost Personal Allowance: That £0.50 of previously tax-free allowance now becomes taxable at 40%. That's an extra 20p of tax (£0.50 × 40%).

Total tax on that extra £1: 40p + 20p = 60p.

Effective marginal rate: 60%.

Note: National Insurance also applies, typically adding 2% on income above £50,270. The combined effective marginal rate in the taper zone is therefore approximately 62% of each extra pound earned.

Who Does the Taper Affect?

The taper applies to your adjusted net income — not simply your salary. This is a broader number that includes:

Counts toward the threshold:

• Salary and wages
• Self-employment profits
• Rental income (after allowable expenses)
• Dividend income (above the £500 dividend allowance)
• Savings interest (above the Personal Savings Allowance)
• Benefits in kind reported on your P11D
• Bonus payments

Does not count (or reduces the threshold):

• Pension contributions (pension contributions reduce adjusted net income)
• Gift Aid donations (these extend the basic rate band, reducing the effective adjusted net income)
• Certain allowable employment expenses

The Strategies to Escape the Trap

Strategy 1: Pension Contributions (The Most Powerful Tool)

A pension contribution reduces your adjusted net income directly. If your adjusted net income is £110,000 and you contribute £10,000 to a pension, your adjusted net income falls to £100,000 — just at the taper boundary.

Here is why this is so powerful:

• You receive 40% income tax relief on the pension contribution (as a higher-rate taxpayer).
• You also restore Personal Allowance at the rate of £1 for every £2 of adjusted net income you reduce.
• A £10,000 pension contribution restores £5,000 of Personal Allowance, which saves an additional 40% × £5,000 = £2,000 of income tax.
• Total tax saving on a £10,000 pension contribution: £4,000 (basic) + £2,000 (PA restoration) = £6,000.
• Net cost of a £10,000 pension contribution: £4,000.

Example: Your gross salary is £115,000. Your Personal Allowance is currently £7,430 (tapered from £12,570). A pension contribution of £15,000 (gross) would bring your adjusted net income to £100,000, fully restoring the £12,570 Personal Allowance. Tax saving: £15,000 × 40% + £5,140 × 40% = £6,000 + £2,056 = £8,056. Net cost of the £15,000 contribution: £6,944.

Strategy 2: Salary Sacrifice

If your employer offers salary sacrifice, it achieves the same tax reduction as a pension contribution but also saves employee and employer National Insurance. For taper purposes, the effect is the same: salary is reduced below the threshold.

Strategy 3: Gift Aid Donations

Charitable donations under Gift Aid extend the basic rate band by the grossed-up donation amount. For income tax purposes, this has a similar (though not identical) effect to pension contributions — it can reduce the income tax you owe, though the mechanism is different from adjusting your actual adjusted net income.

If you already make substantial charitable donations, ensure you are claiming Gift Aid on all of them and reporting them on your Self Assessment return.

Strategy 4: Pension Contributions for a Spouse or Civil Partner

If your spouse or civil partner is a basic-rate taxpayer, there may be planning opportunities to shift income-generating assets between you to keep both incomes in tax-efficient positions. This is a complex area — speak to a tax adviser before restructuring investments between spouses.

The Trap in Retirement

The taper does not only apply during your working years. It can also catch you in retirement if large SIPP withdrawals push your total income above £100,000.

Example in retirement:

• State Pension: £11,502
• SIPP withdrawal: £90,000
• Other income: £3,000 (rental)
• Total adjusted net income: £104,502

In this scenario, £4,502 of Personal Allowance is lost. The effective tax on the marginal income pushing you above £100,000 is 60%.

The solution is to use ISA withdrawals to supplement income instead of taking large SIPP withdrawals. Since ISA withdrawals don't count as income, you can draw down your ISA alongside your SIPP without affecting the taper calculation.

Better strategy:

• State Pension: £11,502
• SIPP withdrawal: £68,000 (below £80,000 to stay well clear of the taper)
• ISA withdrawal: £25,000 (tax-free, no income interaction)
• Other income: £3,000
• Adjusted net income for taper: £82,502 — well below £100,000. Full Personal Allowance retained.

Common Mistakes

Accepting a pay rise without checking the after-tax impact. A salary increase from £99,000 to £110,000 sounds like a £11,000 raise. It's actually a take-home increase of approximately £4,400 (40% rate on the income, plus the 60% effective rate in the taper).

Not contributing to a pension when in the taper zone. This is the most expensive mistake. Every pound you fail to contribute to a pension in the taper zone is a pound where you are leaving 60p of tax saving on the table.

Taking a large end-of-year bonus that tips you into the taper. If you know a bonus will push you above £100,000, ask your employer about timing, or immediately make a pension contribution to bring your adjusted net income back below the threshold.

Ignoring investment income. Rental income, dividends above the £500 allowance, and savings interest all count. Someone with a salary of £95,000 and £6,000 of rental profit is in the taper zone even though their salary is below £100,000.

Withdrawing too much from a SIPP in one year. In retirement, a single large SIPP withdrawal can create a taper liability for that year. Spreading withdrawals across multiple tax years can preserve the Personal Allowance.

What Happens Above £125,140?

Above £125,140, the Personal Allowance is completely gone. You pay 45% additional rate on income above £125,140. National Insurance remains at 2% above £50,270. The combined marginal rate above £125,140 is approximately 47%.

This is lower than the 60%+ in the taper zone — which is why the income range £100,000–£125,140 is so perverse. You can actually pay more tax on income of £110,000 than you would on £125,141 in some circumstances.

Summary

The Personal Allowance taper creates a 60% effective marginal rate for any income between £100,000 and £125,140 in 2024/25. It affects salary earners, the self-employed, landlords, investors, and retirees with large SIPP withdrawals alike.

The most powerful response is pension contributions, which reduce adjusted net income below the threshold while attracting 60% effective relief — the most tax-efficient savings vehicle in the UK tax system.

If your income is approaching or exceeding £100,000 from any combination of sources, calculate your adjusted net income carefully and prioritise pension contributions to reduce it below the taper threshold.

For a personalised model that shows how pension contributions affect your lifetime tax bill and retirement projections simultaneously, use the Selvox calculator.