How income tax actually works (it's weirder than you think)

Income tax looks simple on a payslip. Underneath, it's a system with hidden bands, cliff edges and stacking rules that catch people out every year. Here's how it fits together.

(Note: these are the rates for England, Wales and Northern Ireland. Scotland sets its own bands and rates for most income.)

The basic structure

Everyone starts with a personal allowance of £12,570 — income below this is tax-free. Above that:

• Basic rate: 20% on income from £12,571 to £50,270
• Higher rate: 40% from £50,271 to £125,140
• Additional rate: 45% above £125,140

Crucially, these are marginal rates — moving into a higher band only means the income above the threshold is taxed at the higher rate. Nobody has ever been made worse off by a pay rise pushing them "into the next band" through income tax alone (cliff edges elsewhere are another matter — read on).

The hidden 60% band

Here's the bit that surprises people. Once your income passes £100,000, your personal allowance is withdrawn at £1 for every £2 of income above the threshold. It's fully gone by £125,140.

Losing allowance while paying 40% tax creates an effective rate of 60% on income between £100,000 and £125,140. It's the highest marginal rate in the mainstream system, and it isn't printed in any tax table. Pension contributions are the classic fix — a contribution that brings your income back below £100,000 gets 40% relief and restores your personal allowance, an effective 60% saving. Few tax planning opportunities are this clean.

Different income, different rules

Not all income is taxed the same way, and it stacks in a set order: broadly earnings and rental income first, then savings interest, then dividends.

Savings interest benefits from the personal savings allowance — £1,000 tax-free for basic rate taxpayers, £500 for higher rate, nothing for additional rate. Lower earners may also get up to £5,000 of interest tax-free under the starting rate for savings.

Dividends have their own allowance (£500) and their own rates: 8.75%, 33.75% and 39.35% depending on your band.

The stacking order matters because income near a threshold can push other income into a higher band — one reason DIY tax estimates often come out wrong.

The other cliff edges

Beyond the 60% band, watch for: the High Income Child Benefit Charge, which claws back Child Benefit between £60,000 and £80,000 of income; the loss of tax-free childcare and free childcare hours entitlement once either parent's adjusted income passes £100,000 (a genuine cliff edge — £1 over can cost thousands); and the personal savings allowance halving as you cross into higher rate.

Why this matters

Almost all of these thresholds respond to pension contributions and Gift Aid, both of which reduce your "adjusted net income." Someone at £102,000 with young children may find a £2,000 pension contribution effectively costs them almost nothing once the tax relief, restored allowance and retained childcare support are counted. That's not a loophole — it's the system working as designed for people who understand it.

This article is for general education only and isn't personal advice or tax advice. If your income sits near any of these thresholds, it's worth getting your position checked.