Every payday, a chunk of your salary disappears before it even hits your account. You know it’s “tax,” but if someone asked you to explain exactly how much you pay and why, you’d probably go quiet. You’re not alone — income tax in the UK is one of those things everyone pays and almost nobody fully understands.
Part of the confusion is a myth that refuses to die: that earning more can leave you worse off because you “move into a higher tax bracket.” That’s not how it works, and understanding why will make the whole system click into place.
This article walks through what income tax actually is, how the bands work, what you keep tax-free, and how to check you’re not accidentally overpaying.
What income tax actually is
Income tax is money taken from what you earn — your salary, self-employment profit, pension income, and some other income types — and paid to the government. It funds things like the NHS, schools, roads, and benefits.
For most employees, you never see this money. Your employer calculates it and sends it straight to HMRC (HM Revenue & Customs, the UK’s tax authority) before you’re paid. This system is called PAYE — Pay As You Earn. If you’re self-employed, you calculate and pay it yourself, usually through a Self Assessment tax return.
Income tax is separate from National Insurance (NI), another deduction you’ll see on your payslip. NI is technically a different tax with its own rules, but it comes out alongside income tax, which is why your take-home pay feels a lot smaller than your salary.
The personal allowance: your tax-free chunk
Before any tax is calculated, everyone gets a personal allowance — an amount you can earn each tax year completely tax-free. For most people, this is £12,570.
That means if you earn £12,570 or less in a tax year, you pay no income tax at all. Earn above that, and tax only applies to the amount over £12,570 — not your whole salary.
The personal allowance has been frozen at this level for several years, and the freeze is set to continue for now. A frozen allowance combined with rising wages means more people drift into paying tax, or into a higher band, over time — even without a pay rise that feels significant. This effect is sometimes called “fiscal drag,” and it’s worth knowing the term because it explains why your tax bill can creep up even when your real spending power hasn’t.
If you earn over £100,000, your personal allowance starts shrinking. For every £2 you earn above £100,000, you lose £1 of allowance. By £125,140, it’s gone completely, and you’re taxed on your full income.
How the bands actually work (the bit everyone gets wrong)
This is the biggest misconception in UK income tax: people think that moving into a higher band means all your income gets taxed at the higher rate. It doesn’t. The UK uses a marginal tax system — each band of your income is taxed at its own rate, like filling buckets one at a time.
Here’s the breakdown for England, Wales, and Northern Ireland (Scotland has its own bands — more below):
| Band | Taxable income (after personal allowance) | Tax rate |
|---|---|---|
| Personal allowance | Up to £12,570 | 0% |
| Basic rate | £12,571 – £50,270 | 20% |
| Higher rate | £50,271 – £125,140 | 40% |
| Additional rate | Over £125,140 | 45% |
So if you earn £55,000 a year, you don’t pay 40% on all of it. You pay:
- 0% on the first £12,570
- 20% on the next chunk, up to £50,270
- 40% only on the remaining £4,730 (the bit above £50,270)
Your overall “effective” tax rate — the actual percentage of your total income that goes to tax — ends up well below the top rate you technically reach. This is why earning a bit more will never leave you with less take-home pay overall. You might joke with colleagues that a pay rise “isn’t worth it” because of tax — it is. The only genuine exception is around £100,000–£125,140, where the shrinking personal allowance pushes your effective rate on that slice unusually high, which we’ll cover next.
The £100,000 trap
Between £100,000 and £125,140, something unusual happens. You’re losing £1 of tax-free allowance for every £2 you earn, on top of paying 40% tax on that income. The combined effect means your effective marginal rate in this band works out at roughly 60% — higher than the official “additional rate” of 45% that only kicks in above £125,140.
This is one of the strangest quirks in the UK tax system, and most people earning in this range have no idea it’s happening until they see their payslip or tax calculation. If you’re approaching £100,000, this is worth understanding properly, because pension contributions can sometimes bring your taxable income back under the threshold — effectively buying back your personal allowance. That’s a decision worth thinking through carefully rather than acting on blindly, but it’s the reason some higher earners contribute more to their pension in these years specifically.
Scotland does it differently
If you live in Scotland, your income tax bands aren’t the same as the rest of the UK. The Scottish Parliament sets its own rates, and there are more bands, with different thresholds. Scottish taxpayers generally pay a bit more tax on income above the basic rate band compared to the rest of the UK, though the personal allowance itself is the same across the whole country.
If you’re in Scotland, don’t assume the table above applies to you — check your tax code and the current Scottish bands directly, because they’re reviewed and can change each year.
How to check you’re paying the right amount
Your tax code — a short combination of numbers and letters on your payslip — tells your employer how much tax-free allowance to apply. The most common code is 1257L, reflecting the standard £12,570 allowance. If your code looks different, it might be correct (for example, if you have other income, owe tax from a previous year, or get a benefit through work), but it’s worth understanding why.
Common situations that affect your tax code:
- Starting a new job partway through the tax year
- Having more than one job or pension
- Receiving taxable benefits from your employer (like private medical insurance)
- Owing tax from a previous year that’s being collected gradually
You can check your tax code and what it means using HMRC’s income tax checker. If it looks wrong, contact HMRC directly — getting it fixed can mean a refund if you’ve been overpaying, or avoiding a nasty bill if you’ve been underpaying.
What counts as taxable income (and what doesn’t)
Not everything you receive counts toward your taxable income. Broadly:
Usually taxable: salary, bonuses, self-employment profit, most pension income, rental income, some benefits.
Usually tax-free: ISA interest and growth, the first £1,000 of savings interest for basic rate taxpayers (£500 for higher rate), certain benefits like Universal Credit, and income within your personal allowance.
This is also why ISAs (Individual Savings Accounts) get recommended so often — any interest or investment growth inside one is shielded from income tax entirely, which matters more now that more people are drifting into higher bands.
The bottom line
- Nobody loses money overall by earning more — the UK’s marginal tax system means only the income within a higher band gets taxed at that higher rate, not your whole salary.
- Check your tax code this week. A wrong code is common and easy to fix, and it could mean money owed back to you.
- If you’re nearing £100,000 in income, understand the effective 60% zone between £100,000 and £125,140 before it catches you by surprise at tax time.
- If you’re in Scotland, don’t assume UK-wide figures apply — check the Scottish-specific bands, which differ from the rest of the UK.
- Use your tax-free allowances properly — your £12,570 personal allowance, your ISA allowance, and your savings interest allowance all reduce what you actually pay, and none of them require any special paperwork to benefit from.
Next read: How to check if you’re on the right tax code | https://moneyunpacked.com/tax-code-check/