How Income Tax bands work
Everyone gets a tax-free Personal Allowance of £12,570 for 2026/27. Above that, income is taxed in bands: 20% on earnings up to £50,270, 40% between £50,270 and £125,140, and 45% above that — and like any banded tax, only the portion of income in each band is taxed at that band's rate.
If you earn over £100,000, your Personal Allowance shrinks by £1 for every £2 you earn above that threshold, disappearing entirely at £125,140. This creates an unusually high effective tax rate on the slice of income between £100,000 and £125,140, since you're paying 40% tax while also losing tax-free allowance at the same time.