What HMRC actually takes from £4,000 of side income depends on the salary it sits on top of. £1,000 is covered by the trading allowance; the remaining £3,000 is taxed at your marginal rate.
| Salary | Tax + NI | You keep | Effective rate |
|---|---|---|---|
| £15,000 | £600 | £3,400 | 15% |
| £20,000 | £600 | £3,400 | 15% |
| £25,000 | £600 | £3,400 | 15% |
| £30,000 | £600 | £3,400 | 15% |
| £35,000 | £600 | £3,400 | 15% |
| £40,000 | £600 | £3,400 | 15% |
| £45,000 | £600 | £3,400 | 15% |
| £50,000 | £1,146 | £2,854 | 29% |
| £60,000 | £1,200 | £2,800 | 30% |
| £80,000 | £1,200 | £2,800 | 30% |
| £100,000 | £1,800 | £2,200 | 45% |
Rules checked 18 August 2026 against GOV.UK pages showing the 2026/27 tax year. This is information, not tax advice; your Self Assessment is the authority on what you actually owe.