Register for Self Assessment by 5 October: side income over £1,000, rent, selling on Vinted and eBay

5 October 2026 is the last day to tell HMRC about income for the past tax year (6 April 2025 to 5 April 2026) if you have never filed a tax return before. This is not the return itself — it is registration for Self Assessment: HMRC then issues a UTR number, without which a return cannot be filed. The deadline is set out on GOV.UK and covers any untaxed income — from weekend decorating jobs to renting out a room or selling on marketplaces.

Who must register for 2025/26

You need to register if at least one of the following applied in 2025/26. Income from self-employment or a side hustle above £1,000 before expenses — that is the trading allowance threshold for small earners: tutoring, deliveries, home beauty treatments, cakes to order, freelancing. Rental income — as a rule, if it was above £2,500 a year after expenses (or above £10,000 before expenses). Being a partner in a partnership — each partner registers individually. Child Benefit where one parent's income is above £60,000 — the High Income Child Benefit Charge can now be paid through your tax code instead, but you must opt for that separately, otherwise a return is due. Finally, untaxed income such as dividends, gains from selling shares or cryptocurrency, and foreign income. Interest on savings usually does not require a return — banks report it to HMRC, which bills you by letter: we covered how the P800 process works.

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What HMRC already knows about side hustles

Hoping that "nobody will notice small change" no longer works. Since 2024 digital platforms have been required to collect seller data, and since January 2025 to pass it to HMRC every year: the rule covers eBay, Vinted, Etsy, Depop, Airbnb, Uber, Deliveroo and others. Anyone with roughly 30 or more sales a year, or takings of about €2,000 (around £1,700), is reported. Data also arrives from platforms based abroad — it is a common OECD standard. Where the numbers do not match the tax records, HMRC sends "nudge letters" inviting people to settle up before a formal enquiry begins.

One important caveat: selling your own unwanted belongings — clothes, a pushchair, an old phone — is not trading and is not taxed. The line is crossed when you start buying or making things specifically to resell. Another one: the government has promised to raise the reporting threshold for trading income from £1,000 to £3,000, but the change is not yet in force — the old rule applies to 2025/26 income.

How to register and what happens if you are late

Registration is done online at GOV.UK (the Register for Self Assessment page) through a Government Gateway account; the self-employed are signed up for National Insurance contributions at the same time. The UTR usually arrives by post within 10 working days, longer from abroad — so leaving it to the last day is unwise, and if you miss 5 October you should still register as soon as possible. The deadlines after that: paper returns by 31 October 2026, online returns by 31 January 2027, and payment of the tax also by 31 January 2027.

There is usually no penalty for registering late as such, provided the tax is paid on time in the end. A late return, however, is penalised automatically: £100 immediately after the deadline even if no tax is due, then £10 a day after three months, and more beyond that. If tax ends up unpaid because of late registration, a percentage-based penalty and late-payment interest are added.

Those whose self-employment and rental income for 2024/25 exceeded £50,000 should remember the next step: since April 2026 they have been moved to quarterly reporting under Making Tax Digital — HMRC signs people up automatically, with the next quarterly update due by 7 November. And families receiving Child Benefit may find our guide to the rules and the charge above £60,000 useful.