Do I need to register for Self Assessment for a side hustle?

Last verified: 26 August 2026, against the cited gov.uk and HMRC sources.

Two questions decide this, in order: were you trading? and was the gross over £1,000? Everything else — the forms, the UTR, the penalties — follows from those two answers.

Question 1: were you trading, or clearing out?

Selling personal possessions is not a side hustle. HMRC's guidance says that if you're selling personal possessions, "you probably do not have to pay Income Tax on these" — things you bought or were given for your own use and no longer want (gov.uk: check if you need to tell HMRC about income from online platforms). A wardrobe clear-out that raises £3,000 does not put you into Self Assessment.

Trading is different. The same guidance says you're "probably trading if you sell goods that you have bought intending to sell for a profit", and the same applies to items you made, "including items you make for a hobby". The reseller, the Etsy maker, the dog walker, the freelance designer, the content creator taking brand payments — all trading.

Genuinely unsure? HMRC publishes a free online checker on that page — "Use this tool to check if you need to tell us about income you receive from using online platforms" — and gov.uk has a second free tool covering Self Assessment generally: check if you need to send a tax return for the 2025 to 2026 tax year. Both are free and take a few minutes.

Question 2: was the gross over £1,000?

The trading allowance is "a tax exemption of up to £1,000 a year for individuals with trading income" (gov.uk). Three details decide more cases than anything else on this page:

• It's gross, not profit. gov.uk defines it: "Gross income means the total amount you would put on your tax return before any allowances or expenses are taken off." £1,300 of sales with £700 of costs is over the line, even though you cleared £600.
• It's one allowance across everything you do. HMRC's online-platforms guidance says to "add together this income with your income from other trading activities, such as selling goods or providing services". Depop plus dog-walking plus a bit of freelance work share a single £1,000.
• It's the tax year, not the calendar year. 6 April to 5 April. Platform emails run on the calendar year, which is a different thing entirely — see below.

Being employed alongside it changes nothing about this test. PAYE deals with your salary; the trading income is assessed separately, and the return is what brings the two together. Other things can also drag you into Self Assessment regardless of a side hustle — being a partner in a business partnership, Capital Gains Tax, the High Income Child Benefit Charge, rental income, untaxed savings or dividends (gov.uk: who must send a tax return).

Which 5 October is yours?

Registration is an earlier, separate deadline from filing. gov.uk: "You must tell HM Revenue and Customs (HMRC) by 5 October 2026" if you need to complete a return for 2025-26 (gov.uk: Self Assessment deadlines).

So if your side hustle passed £1,000 at any point during the year that ended on 5 April 2026, 5 October 2026 is your deadline and it is weeks away. If you passed £1,000 for the first time this summer, you're in the 2026-27 year and your deadline is a year later — but the record-keeping starts now, because the figure you'll need is a full year of gross income. The paper filing deadline for 2025-26 is 31 October 2026 and the online one is 11:59pm on 31 January 2027, with payment due the same day (gov.uk). Our Q4 2026 deadline calendar puts all of these in order.

How you actually register

You register online at gov.uk/register-for-self-assessment. You need to register if you've never sent a tax return before, or if you registered previously but didn't send one for the year before — in which case gov.uk notes "you may need to reactivate your Self Assessment account" rather than start from scratch.

What you get is a Unique Taxpayer Reference (UTR), the ten-digit number every return is filed against. It doesn't arrive instantly: gov.uk tells people "If you're waiting for a Unique Taxpayer Reference (UTR), you can check when you can expect a reply from HMRC" — which is the honest answer to "how long does it take", and the practical reason to register in September rather than late January. Activating the online account is a further step after the UTR arrives.

Registering is not the same as filing, and it is not a bill. It puts you on the list so that a return can exist.

The penalty for registering late is not the £100 one

This is the part most side-hustle guides skip. The famous £100 is the late filing penalty — automatic, charged even if you owe nothing, then £10 a day up to £900 after three months, then 5% of the tax due or £300 (whichever is greater) at six months and again at twelve (gov.uk: penalties). Missing registration is a different failure with its own regime.

First, the soft landing: if you register after 5 October, "HMRC will send you a letter or email with a different deadline to send your tax return by - this will be 3 months from the date on the letter or email" (gov.uk). Your payment deadline does not move — it stays 31 January — so late registration compresses the time you have to work out and fund the bill.

Second, the actual penalty. A failure to notify penalty is charged as a percentage of the "potential lost revenue" — for Income Tax, the tax that is unpaid at the 31 January following the tax year. The percentage depends on your behaviour, on whether you came forward yourself (unprompted) or only after HMRC made contact (prompted), and on whether you told them within 12 months of the tax being due (HMRC factsheet CC/FS11):

Read the top-left cell carefully, because it is the whole argument for acting now: a non-deliberate failure, disclosed unprompted within 12 months, starts at 0%. The gap between putting your hand up and waiting for a letter is measured in tens of percent of your tax bill. HMRC also states that where you have a reasonable excuse for a non-deliberate failure to notify — "something that stopped you from meeting a tax obligation on time which you took reasonable care to meet" — no penalty is charged. Reasonable excuse does not rescue a deliberate failure.

What registering does and doesn't mean

• It doesn't mean you'll owe tax. That depends on profit, allowances and your other income, all calculated on the return.
• You choose the allowance or your expenses, never both. Over £1,000 you can deduct the flat £1,000 trading allowance instead of your costs — but "You cannot deduct any other expenses or allowances if you claim the allowances" (gov.uk). Whichever number is larger is worth more to you.
• Under £1,000, filing is sometimes still worth it. HMRC's SA103S notes flag that you need to file if you want to pay Class 2 National Insurance voluntarily to protect your State Pension record. For 2025-26 the Class 2 small profits threshold was £6,845 and the voluntary rate £3.50 a week; for 2026-27 the voluntary rate is £3.65 a week (gov.uk: NIC rates and allowances, gov.uk: self-employed NI rates). If you're employed as well, your employment record may already cover the year — check your State Pension forecast before paying for something you have.
• Records start immediately. "You must keep your records for at least 5 years after the 31 January submission deadline of the relevant tax year" (gov.uk: how long to keep your records) — for a 2025-26 return, that means until at least 31 January 2032.

Once you're registered, the self-employment pages are the SA103: the short version if your turnover was below the VAT threshold of £90,000, the full version above it (gov.uk: SA103S, gov.uk: VAT threshold). HMRC's own online service is free — no filing software to buy. Our first Self Assessment walkthrough covers the forms, the rates and the Payments on Account cash-flow shock that catches most first-timers.

A platform email is not a registration trigger

The thing that prompts most people to search this question is a message from Vinted, eBay or Etsy about sharing data with HMRC. That's a different rule on a different calendar. Platforms report sellers who pass roughly 30 sales or €2,000 (about £1,700) on that platform in a calendar year, and gov.uk says plainly that "A platform reporting your details to HMRC does not automatically mean you owe tax" (gov.uk: selling goods or services on a digital platform). Platforms collect the information yearly and send it to HMRC by the following January, and they must give you a copy.

So the two lines can fire independently: 45 sales of your own old clothes gets you reported and owes nothing; £4,000 of quiet reselling means registration whether or not any platform reports you. The full comparison is in our Vinted/eBay HMRC letter answer.

One thing to check before 2027

If your side hustle grows, Making Tax Digital for Income Tax eventually replaces this annual rhythm with quarterly updates. It already applies to people whose qualifying income was over £50,000 in 2024-25; over £30,000 in 2025-26 brings you in from 6 April 2027, and over £20,000 in 2026-27 from 6 April 2028 (gov.uk: check if you're eligible for MTD for Income Tax). Qualifying income is "your total income from self-employment and property... the amount before expenses" (gov.uk: work out your qualifying income) — combined and gross, like the £1,000 test. Our MTD page covers what that looks like in practice.

Quick answers

My side hustle made £1,200 but I only profited £200. Do I register?

Yes. The test is gross income before expenses, and £1,200 is over £1,000 (gov.uk). Whether any tax is actually due is a separate question answered on the return.

I have a full-time job. Does PAYE cover it?

Not for the side income. PAYE deals with your salary; trading income over £1,000 still needs a return (gov.uk).

I passed £1,000 in June 2026. What's my deadline?

You're in the 2026-27 tax year, so you must tell HMRC by 5 October 2027 and file online by 31 January 2028.

I should have registered last year and didn't.

Register now rather than waiting to be contacted. A non-deliberate failure disclosed unprompted within 12 months of the tax being due carries a penalty range starting at 0% of the potential lost revenue; a prompted disclosure after 12 months starts at 20% (CC/FS11). If the amounts are significant, this is the point to involve an accountant.

Do I need to register if I sold one valuable personal item?

Not for trading — but selling a personal possession for £6,000 or more can raise Capital Gains Tax instead, and sets of things count together. Cars are exempt (gov.uk: CGT on personal possessions).

Do I have to buy software to file?

No. HMRC's online Self Assessment service is free. That changes only when Making Tax Digital reaches your income level.