Comprehensive UK Income Tax Guide

For UK employees who want to understand how Income Tax is actually applied to their pay — not just the headline rates, but how the Personal Allowance, progressive bands and the £100,000 trap interact. It complements the take-home pay guide (which covers the full payslip including NI and pensions) by focusing on Income Tax mechanics and the decisions that shift which band you sit in.

How progressive bands actually work

A common misconception is that crossing a threshold taxes your whole salary at the higher rate. It does not. Only the portion of income above each threshold is taxed at that rate. On a £45,000 salary in England:

• First £12,570: tax-free (Personal Allowance)
• £12,571 – £45,000 at 20%: £6,486
• Total Income Tax: £6,486 — not 20% of £45,000.

The 2026/27 bands at a glance

Scotland uses different bands and rates — see GOV.UK: Scottish Income Tax.

The £100,000 Personal Allowance trap

For every £2 of adjusted net income above £100,000, you lose £1 of Personal Allowance. By £125,140 the allowance is gone entirely. In that band, each extra £2 is taxed at 40% and exposes another £1 (previously tax-free) to 40% — an effective marginal rate of 60%. This is the steepest spike in the UK tax system, and it is the main reason higher earners channel income above £100,000 into pensions.

Worked example: the 60% band

Someone earning £110,000 has £10,000 above the £100,000 threshold.

• That £10,000 is taxed at 40% = £4,000.
• It also strips out £5,000 of Personal Allowance, which becomes taxable at 40% = another £2,000.
• Effective tax on that £10,000: £6,000 — a 60% marginal rate.
• Putting £10,000 into a pension instead brings adjusted net income back to £100,000, restoring the full allowance and avoiding the trap.

Relief that genuinely reduces taxable income

• Pension contributions — extend your basic-rate band or reduce adjusted net income; the most powerful lever for higher earners.
• Gift Aid donations — extend your basic-rate band, and higher-rate payers claim the extra relief via Self Assessment.
• Marriage Allowance — worth £252/year where one spouse does not use their full allowance and the other is a basic-rate payer.
• Specific employment expenses — limited, but includes professional subscriptions and some working-from-home costs under the rules at GOV.UK: Tax relief for employees.

When you need a Self Assessment

Not just for the self-employed. You generally need to file if you earn over £100,000, have income from property or investments above the relevant limits, are a company director, or have foreign income. Check at GOV.UK: Check if you need a tax return.

Limitations

Bands and the Personal Allowance taper are 2026/27 figures for England, Wales and Northern Ireland and change each Budget. Scottish bands differ. This is educational, not advice; for complex planning — especially around the £100,000 trap, tapered pension allowances, or cross-border income — an FCA-regulated adviser is worthwhile. Model your own bands with the UK Salary Calculator.