What a side hustle actually costs in tax, at your salary — not at some imaginary average one. Every figure is computed from the 2026/27 rules published on GOV.UK, with the trading allowance handled properly.
| Side income | Tax + NI | You keep |
|---|---|---|
| £500 | £0 | £500 |
| £1,000 | £0 | £1,000 |
| £1,500 | £100 | £1,400 |
| £2,000 | £200 | £1,800 |
| £2,500 | £300 | £2,200 |
| £3,000 | £400 | £2,600 |
| £4,000 | £600 | £3,400 |
| £5,000 | £800 | £4,200 |
| £6,000 | £1,000 | £5,000 |
| £8,000 | £1,400 | £6,600 |
| £10,000 | £1,800 | £8,200 |
| £12,000 | £2,200 | £9,800 |
| £15,000 | £2,886 | £12,114 |
| £20,000 | £4,186 | £15,814 |
Pick your amount above, then your salary — the rate changes a lot more with salary than people expect.
1. The first £1,000 is free. The trading allowance covers your first £1,000 of gross side income — no tax, and below that, no Self Assessment either.
2. Side income stacks on top of your salary. It fills your next tax band, not your first one. The same hustle can be taxed at 0%, 20%, 40% or effectively 60% depending on what you already earn.
3. National Insurance barely matters until it really does. Class 4 NI only starts once self-employment profits alone pass £12,570 — most side incomes never get there.
Income tax bands and the personal allowance taper from GOV.UK income tax rates, the trading allowance from GOV.UK tax-free allowances, and National Insurance from GOV.UK self-employed NI rates — all read from pages showing the 2026/27 year on 18 August 2026. Scottish bands differ (see GOV.UK); these pages cover England, Wales and Northern Ireland.
If a figure here is wrong, it is a mistake rather than a marketing choice, and it gets corrected with the date it changed.
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.