What HMRC actually takes from £20,000 of side income depends on the salary it sits on top of. £1,000 is covered by the trading allowance; the remaining £19,000 is taxed at your marginal rate.
| Salary | Tax + NI | You keep | Effective rate |
|---|---|---|---|
| £15,000 | £4,186 | £15,814 | 21% |
| £20,000 | £4,186 | £15,814 | 21% |
| £25,000 | £4,186 | £15,814 | 21% |
| £30,000 | £4,186 | £15,814 | 21% |
| £35,000 | £4,932 | £15,068 | 25% |
| £40,000 | £5,932 | £14,068 | 30% |
| £45,000 | £6,932 | £13,068 | 35% |
| £50,000 | £7,932 | £12,068 | 40% |
| £60,000 | £7,986 | £12,014 | 40% |
| £80,000 | £7,986 | £12,014 | 40% |
| £100,000 | £11,786 | £8,214 | 59% |
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.