Why your tax isn't a flat percentage
UK income tax is progressive. The first £12,570 (the personal allowance) is tax-free; then income is taxed at 20% (basic), 40% (higher) and 45% (additional). Crucially, only the income within each band is taxed at that band's rate.
Watch the £100,000 trap: above it, the personal allowance tapers away, creating an effective 60% marginal rate on that slice of income.
Common questions
The first £12,570 of income is tax-free. It tapers away by £1 for every £2 you earn over £100,000, disappearing entirely at £125,140.
Your marginal rate is the band your last pound falls into (20/40/45%). Your effective rate is total tax over total income — always lower.
No, this is income tax only. Use the take-home calculator for the full deductions picture.