UK £100k Tax Trap Calculator

The UK's £100k tax trap is one of the most punishing features of the UK tax system. When your income exceeds £100,000, you begin losing your £12,570 Personal Allowance at a rate of £1 for every £2 earned above the threshold.

This creates an effective marginal tax rate of 62% on income between £100,000 and £125,140:

• 40% Higher Rate income tax
• 2% National Insurance (above Upper Earnings Limit)
• 20% effective rate from Personal Allowance loss (50% of 40%)

By £125,140, your Personal Allowance is completely gone. The "trap zone" affects approximately 725,000 workers in 2024/25, projected to reach 2.3 million by 2029 as wage growth drags more people across the threshold.

The most effective strategy for employed high earners is pension contributions via salary sacrifice. By reducing your taxable income below £100,000, you restore your full Personal Allowance.

For example, if you earn £120,000:

• You're £20,000 into the trap zone
• You've lost £10,000 of Personal Allowance (£20k × 50%)
• This costs you £4,000 extra tax (£10k × 40%)
• Contributing £20,000 to pension restores the full PA and saves £4,000+ in tax

The beauty of salary sacrifice is that you save both income tax AND National Insurance, unlike personal pension contributions which only receive tax relief.

While the Personal Allowance taper rules apply across the UK, Scotland has different income tax bands:

• Starter Rate (19%): £12,571 - £14,876
• Basic Rate (20%): £14,877 - £26,561
• Intermediate Rate (21%): £26,562 - £43,662
• Higher Rate (42%): £43,663 - £75,000
• Advanced Rate (45%): £75,001 - £125,140
• Top Rate (48%): Over £125,140

Scottish taxpayers in the trap zone face a slightly higher marginal rate (42% vs 40% for the Higher Rate portion), making pension optimization even more valuable.

Between £100,000 and £125,140 your personal allowance shrinks by £1 for every £2 you earn. That mechanism creates a hidden extra tax on top of the standard 40% higher rate.

Here is the arithmetic on a single extra pound of income in that zone:

• You earn £1 above £100,000
• You pay 40p income tax on that £1 (higher rate)
• Your personal allowance falls by 50p (£1 divided by 2)
• That 50p was previously tax-free; it is now taxed at 40%, costing you 20p more
• National Insurance at 2% (above the Upper Earnings Limit) adds 2p
• Total: 62p lost from every £1 earned in this band

The "60% trap" label comes from rounding: 40% tax + 20% effective PA taper = 60%, ignoring the 2% NI. Either way, it is the highest effective marginal rate faced by the vast majority of UK employees.

Worked example: earning £110,000 vs £99,000

Someone earning £99,000 keeps their full £12,570 personal allowance. Their approximate take-home (2024/25, England):

• Personal allowance: £12,570 tax-free
• Basic rate band: 20% on £37,700 = £7,540
• Higher rate: 40% on £48,730 = £19,492
• National Insurance: approximately £5,490
• Take-home: approximately £64,478

Someone earning £110,000 has lost £5,000 of personal allowance (£10k above threshold, divided by 2):

• Personal allowance: only £7,570 tax-free (£12,570 - £5,000)
• Tax and NI on the extra £11,000 of income: approximately £6,820 (at the 62% effective rate)
• Take-home: approximately £69,170

The person earning £110,000 takes home only about £4,692 more than the person on £99,000 despite earning £11,000 more gross. That extra gross income was taxed at an average rate of 57%.

The goal is simple: reduce your adjusted net income (the figure HMRC uses for personal allowance purposes) to £100,000 or below. Several routes exist.

1. Pension contributions via salary sacrifice

This is the most effective route for most employed people. Your employer reduces your gross salary before PAYE, cutting both income tax and National Insurance. If you earn £120,000, sacrificing £20,000 into your workplace pension:

• Adjusted net income falls to £100,000
• Full personal allowance restored: saves £5,040 in income tax
• NI saving on £20,000 at 2%: saves £400
• Total saving: approximately £5,440 on a £20,000 pension contribution

The effective cost to you is £14,560 to put £20,000 into your pension - a 27% discount, before investment growth.

2. Personal pension contributions (Relief at Source)

If salary sacrifice is not available, you can pay into a personal pension directly. Basic-rate tax relief is added automatically (20%). You then claim the higher-rate relief and the personal allowance restoration through Self Assessment. The cash saving is the same; you just have to wait until your tax return.

3. Gift Aid donations

Charitable donations under Gift Aid reduce your adjusted net income in the same way as pension contributions. If you donate £800 to charity via Gift Aid, HMRC treats it as a £1,000 donation and your adjusted net income falls by £1,000. This restores £500 of personal allowance, saving £200 in tax - on top of the charity receiving tax relief. It is not as efficient as pensions (you give the money away) but genuinely reduces your tax bill.

4. Bonus sacrifice

If your bonus takes you over £100,000, ask whether your employer can pay it directly into your pension as an employer contribution. Many do. This keeps you below the threshold without using any of your annual allowance (employer contributions count separately under different rules). Check with your payroll team well before bonus payment date.

Keep an eye on your annual pension allowance (£60,000 for most people in 2024/25). High earners with total adjusted income above £260,000 face a tapered allowance down to £10,000. If you are anywhere near these limits, a financial adviser will pay for themselves many times over.