The short answer
You normally need to register for Self Assessment if you are trading — buying or making things to sell for profit — and your gross trading income (before any costs) is over £1,000 in a tax year. If you're just clearing out your own unwanted personal belongings, that's generally not trading, so you usually don't need to register at all, however much it comes to.
If you're not sure which side of the line you're on, the side-hustle tax calculator walks through it and estimates any tax due.
Am I "trading", or just selling my own stuff?
HMRC looks at why and how you sell. Signs you're trading include: buying items specifically to resell, making things to sell, selling regularly and repeatedly, and doing it with the intention of making a profit. Signs you're not trading: selling off your own used clothes, old furniture, a games console you've finished with — one-off disposals of things you originally bought to use, not to flip.
Selling your own personal possessions is generally free of Income Tax however much it totals. (Very high-value single items can occasionally raise Capital Gains Tax questions, but that's a separate topic from side-hustle Income Tax.)
The £1,000 trading allowance
If you are trading, there's a tax-free trading allowance of up to £1,000 a year. If your gross trading income is £1,000 or less, it's covered and you generally don't need to tell HMRC. Once you go over £1,000 gross you normally need to register, and you then deduct either the £1,000 allowance or your actual expenses — whichever leaves you paying less. The calculator picks the better of the two for you automatically.
"Vinted asked for my details" — do I have to register now?
Not automatically. Since January 2025, digital platforms must report a seller to HMRC if that seller makes 30 or more sales or receives around £1,700 (€2,000) or more in a calendar year. That's a reporting rule — the platform shares data — not a new tax and not an instruction to register. HMRC's own guidance says being reported "does not automatically mean you owe tax." Whether you need to register still comes down to the trading test and the £1,000 allowance above.
The deadlines that matter
If you decide you do need to register for the 2025/26 tax year (which ran from 6 April 2025 to 5 April 2026):
- Register by 5 October 2026. The rule is: register by 5 October following the end of the tax year you first need to send a return for.
- File online by 11:59pm on 31 January 2027. (A paper return would be due earlier, by 31 October 2026 — most people file online.)
- Pay any tax you owe by 31 January 2027. The filing and payment deadlines fall on the same date.
Missing the registration or filing deadline can trigger penalties, so it's worth diarising 5 October and 31 January.
How to register (the practical steps)
Registration is free and done on gov.uk. In outline:
- Go to the official gov.uk "Register for Self Assessment" page and choose the option that fits you (most side-hustlers register as self-employed / sole trader).
- You'll set up or sign in to a Government Gateway account and get a Unique Taxpayer Reference (UTR) in the post — allow time for this, which is another reason not to leave registration until January.
- When the return is due, you report your gross income and either the £1,000 allowance or your expenses, and HMRC works out the tax.
Keep a simple record of your sales, fees and costs as you go. The calculator produces a printable / CSV summary you can keep alongside your own records.
What might I actually owe?
Your side-hustle profit (income minus the allowance or your costs) stacks on top of your other income and is taxed at your marginal rate — 20% in the basic-rate band, 40% in the higher-rate band. If your total self-employed profit is over £12,570 you may also pay Class 4 National Insurance (6% up to £50,270, 2% above). The side-hustle tax calculator estimates Income Tax and Class 4 NI together for the tax year you pick.