The £100k Tax Trap: Why Earning More Can Leave You Worse Off

If you earn over £100,000 in the UK, you might assume you pay 40% income tax on everything above the higher-rate threshold. But between £100,000 and £125,140, something much worse happens: your effective tax rate hits 60%. For every extra £1 you earn, you lose 60p to tax.

This is the £100k tax trap — and understanding it is one of the most valuable things you can do for both your take-home pay and your retirement planning.

How the Trap Works

Everyone in the UK gets a Personal Allowance of £12,570. That's the amount you can earn before paying any income tax.

But when your adjusted net income exceeds £100,000, you lose £1 of Personal Allowance for every £2 you earn over £100k. By the time you reach £125,140, your Personal Allowance is completely gone.

The Maths

Let's say you earn £110,000:

• You're £10,000 over the £100,000 threshold
• You lose £5,000 of Personal Allowance (£10,000 ÷ 2)
• Your remaining Personal Allowance: £12,570 - £5,000 = £7,570
• That £5,000 of income that was previously tax-free is now taxed at 40%
• Extra tax on the lost allowance: £5,000 × 40% = £2,000

So on that extra £10,000 of earnings above £100k:

• Normal 40% tax: £4,000
• Tax on lost Personal Allowance: £2,000
• Total tax on the £10,000: £6,000 — an effective rate of 60%

Plus National Insurance at 2% on earnings above £50,270, bringing the true marginal rate to 62%.

The Full Picture

Look at that table carefully. Someone earning £130,000 pays a lower marginal rate than someone earning £110,000. The trap is a tax cliff that punishes people in a specific band before returning to normal rates.

Why This Matters for Retirement Planning

If you earn between £100k and £125k, pension contributions are extraordinarily powerful — because they reduce your adjusted net income, which is the figure used to calculate your Personal Allowance.

The Pension Escape Route

Pension contributions (via salary sacrifice or personal contributions with tax relief) reduce your adjusted net income. If you can bring it below £100,000, you:

1. Restore your full Personal Allowance — saving up to £5,028 in tax 2. Get 40% tax relief on the pension contribution itself 3. Save 2% NI if using salary sacrifice 4. Build your retirement pot with money that would otherwise go to HMRC

Example: Salary of £115,000

Without pension contributions (beyond minimum):

• Adjusted net income: ~£115,000
• Lost Personal Allowance: £7,500 (£15,000 ÷ 2)
• Remaining PA: £5,070
• Extra tax from lost PA: £7,500 × 40% = £3,000

With £15,000 pension contribution (salary sacrifice):

• Adjusted net income: £100,000
• Full Personal Allowance restored: £12,570
• Tax saved from restored PA: £3,000
• Income tax relief on contribution: £6,000 (40% of £15,000)
• NI saved (salary sacrifice): £300 (2% of £15,000)
• Total tax/NI saved: £9,300
• Effective cost of putting £15,000 in your pension: £5,700

That's a 62% "return" on your pension contribution from tax savings alone — before any investment growth.

The Numbers Are Even Better Than They Look

That £15,000 going into your pension isn't just saving you tax today. Over 20 years at 5% growth, it becomes roughly £39,800. And you only gave up £5,700 of take-home pay to get there.

Who Falls Into the Trap?

It's not just people on £100k+ base salaries. You can fall in through:

Bonuses. A £85,000 salary with a £20,000 bonus puts you at £105,000. You've lost £2,500 of Personal Allowance.

Overtime or commission. Variable pay can push you over unexpectedly.

Benefits in kind. Company car, private medical insurance, and other taxable benefits add to your adjusted net income.

Rental income. Property earnings count toward the £100k threshold.

Investment gains or dividends. These can push you over too (though dividends have their own allowance).

Redundancy packages. The taxable portion of a redundancy payment can push you into the trap for one year.

Strategies to Escape the Trap

1. Pension Contributions (The Most Effective)

Salary sacrifice is the gold standard:

• Reduces your gross salary below £100k
• Saves income tax AND National Insurance
• Employer also saves NI (some pass this saving back to you)
• Money goes directly into your pension — tax-free growth

Personal pension contributions (SIPP) also work:

• You contribute from net pay
• Basic-rate relief is added automatically (20%)
• You claim higher-rate relief (additional 20%) via self-assessment
• The contribution reduces your adjusted net income

How much to contribute: Enough to bring your adjusted net income to £100,000. If you earn £115,000, contribute £15,000. If you earn £125,140, you'd need to contribute £25,140 to fully escape — though any contribution in this band is highly efficient.

2. Carry Forward Unused Allowance

Your annual pension allowance is £60,000 — but you can also carry forward unused allowance from the previous 3 tax years. This means in some years you could contribute significantly more than £60,000, making a larger dent in a particularly high-earning year (like when receiving a bonus).

3. Charitable Donations (Gift Aid)

Gift Aid donations also reduce your adjusted net income. If you're planning to donate to charity anyway, doing so when you're in the £100k-£125k band is extremely tax-efficient.

The maths: A £1,000 Gift Aid donation:

• Charity receives £1,250 (with basic-rate reclaim)
• You claim £250 higher-rate relief
• Your adjusted net income drops by £1,250
• You regain £625 of Personal Allowance
• Tax saved on restored PA: £250
• Total personal tax benefit: £500 on a £1,000 donation

4. Timing of Income

If you have any control over when you receive bonuses or variable pay:

• Defer income to a tax year where your total will stay below £100k
• Accelerate expenses (like pension contributions) into a high-earning year
• Split income across tax years where possible

This doesn't apply to regular salary, but bonuses, dividends from your own company, and freelance income can sometimes be timed.

The Child Benefit Trap (Another Trap Within the Trap)

If you earn over £60,000, you start losing the High Income Child Benefit Charge (HICBC). Between £60,000 and £80,000, you repay a portion of Child Benefit. Over £80,000, you repay it all.

Pension contributions can help here too — if your adjusted net income drops below £60,000, you keep full Child Benefit. For a family with two children, that's worth about £2,075/year (2026/27 rates).

Combined with the £100k trap, a family with children and income around £100-£110k could be losing:

• 60% marginal tax on income over £100k
• Child Benefit (already fully clawed back)
• Plus the psychological cost of a system that punishes earning slightly more

Common Mistakes

1. Not Realising You're in the Trap

Many people don't check whether their total income crosses £100k until they get an unexpected tax bill via self-assessment. Check your total income (salary + benefits + other income) before the end of each tax year.

2. Thinking It's Not Worth Earning More

Some people avoid payrises or overtime to stay below £100k. This is almost always wrong — the solution is to earn more AND contribute more to pensions, not to earn less. You still keep 38p of every £1 above £100k, and pension contributions can restore the rest.

3. Forgetting to Claim Higher-Rate Relief

If you make personal pension contributions (not salary sacrifice), you get 20% basic-rate relief automatically. But you must claim the additional 20% higher-rate relief via self-assessment. HMRC won't give it to you unprompted. Many higher earners lose thousands by not filing a tax return when they're not required to otherwise.

4. Not Using Salary Sacrifice When Available

Salary sacrifice saves both income tax AND National Insurance. Personal pension contributions only save income tax. If your employer offers salary sacrifice, use it — the NI saving alone is 2% on earnings above £50,270 (or 13.25% below that threshold).

5. Ignoring It Because "It's Only for One Year"

Even if your income only crosses £100k in one year (bonus, redundancy), the trap still applies for that year. A one-off salary sacrifice or pension contribution in that specific year can save thousands.

Real-World Examples

Example 1: Software Developer on £105,000

Situation: Base salary £105,000. No other income. Default workplace pension at 5% employee + 3% employer.

Problem: Adjusted net income after default pension: £105,000 - £5,250 = £99,750. Actually just under! But wait — they have private medical insurance (BIK: £1,200) pushing them to £100,950. They've lost £475 of Personal Allowance.

Solution: Increase pension contribution to 7.4% (£7,770). Adjusted net income: £105,000 - £7,770 + £1,200 = £98,430. Below £100k, full PA restored. Extra tax saved: ~£780 from restored PA + higher-rate relief on the additional contribution.

Example 2: NHS Consultant on £115,000

Situation: NHS salary £115,000. Already in NHS Pension (DB scheme, employee contribution ~13.5%).

Problem: NHS pension contributions are treated differently — they reduce taxable pay but the calculation for adjusted net income is complex with DB schemes. Net income is around £102,000-£105,000 depending on scheme specifics.

Solution: Additional voluntary contributions (AVCs) or a personal SIPP contribution to bridge the gap to £100k. Even £3,000-£5,000 in a SIPP, combined with the NHS pension, could restore the full Personal Allowance.

Example 3: Dual Income Couple, One at £108,000

Situation: One partner earns £108,000, the other £45,000. Two children.

Problem: Higher earner: lost £4,000 PA (extra tax: £1,600). Child Benefit already fully clawed back at this income level.

Solution: Higher earner salary sacrifices £8,000 into pension. Adjusted net income: £100,000. Full PA restored. Tax saved: £1,600 + £3,200 relief on contribution = £4,800 total benefit. Effective cost of £8,000 pension contribution: £3,200.

Planning for Retirement with the £100k Trap in Mind

The tax trap isn't just an annual tax problem — it's a retirement planning opportunity. Every pound you divert into pensions from the £100k-£125k band is money that:

1. Would have been taxed at 60%+ — you're saving it at the highest marginal rate in the UK tax system 2. Grows tax-free inside the pension wrapper 3. Gets taxed at your retirement rate — which for most people will be 0-20%, not 60%

Think about it: you save tax at 62% going in, and pay tax at 20% coming out. That's an immediate 42 percentage point gain before any investment returns.

In Retirement

When you eventually draw from this pension:

• Your first £12,570 is tax-free (Personal Allowance — which you'll fully have in retirement!)
• The next £37,700 is taxed at 20%
• Only amounts above £50,270 face 40%

Most retirees drawing moderate amounts from their pension pay significantly less tax than they did while working. The money you saved at 60% is now being withdrawn at 0-20%.

What Should You Do?

Step 1: Check Your Income

Add up:

• Gross salary
• Bonus and commission
• Benefits in kind (P11D value)
• Rental income
• Dividend income
• Any other taxable income

If the total is between £100,000 and £125,140 — or might be — you're in the trap.

Step 2: Calculate the Optimal Contribution

Work out how much you'd need to contribute to bring your adjusted net income to £100,000. This is your "sweet spot" contribution.

Step 3: Talk to Your Employer

Ask about:

• Salary sacrifice arrangements
• Matching contributions above the default
• Flexible benefits that reduce taxable pay

Step 4: Consider a SIPP

If salary sacrifice isn't available, open a SIPP and make personal contributions. Remember to claim higher-rate relief via self-assessment.

Step 5: Model Your Retirement

Use our calculator to see how those additional pension contributions compound over time. The tax savings are immediate, but the retirement impact is where the real magic happens.

The Bottom Line

The £100k tax trap is one of the most punishing quirks of the UK tax system. But it's also one of the biggest opportunities for tax-efficient retirement saving. If you earn between £100,000 and £125,140, pension contributions aren't just sensible — they're some of the most efficient financial moves you can make.

Every pound you contribute in this band saves you up to 62p in tax and NI. That same pound grows tax-free for decades, then gets withdrawn at a fraction of the rate you saved it at.

The trap is real. But so is the escape route.

Want to see how maximising your pension contributions affects your retirement? Model your retirement income with different contribution levels and see the year-by-year impact on your pension pot.