Anyone in the UK who started earning money outside a payslip during the last tax year has one date to circle this week: 5 October. That is the day by which HM Revenue and Customs (HMRC) expects to be told that you need to file a Self Assessment tax return for the year that ended on 5 April 2026. It applies to first-time filers and to people who registered years ago but were not asked for a return last time. Miss it and HMRC can issue a penalty, even before a single figure of tax is calculated.
Who the 5 October deadline is aimed at
The deadline is not about paying tax. It is about telling HMRC you exist as a taxpayer with income that is not already taxed at source. The most common situations are people who went self-employed, took on freelance work alongside a job, started renting out a room or a property, or built up a side hustle selling goods or services online. Company directors receiving untaxed income, people with sizeable investment income and higher earners who claim child benefit can also find themselves in scope.
If you have filed a return before and HMRC still has you on its books, nothing changes. The notification rule targets those who have never sent a return, or whose record was closed because a return was not needed for the 2024 to 2025 tax year.
The £1,000 line that decides whether you must act
The point at which a hobby becomes a taxable activity is set by the trading allowance. You can receive up to £1,000 of gross trading income in a tax year without telling HMRC or paying anything on it. A second, separate £1,000 allowance covers property income, so someone letting a driveway and occasionally selling handmade items has two thresholds, not one.
The detail that catches people out is the word gross. The £1,000 is measured on money received, not on profit. Sell £1,300 of goods and spend £400 on postage and materials and you are still over the line, because costs are only deducted later, when the return is prepared. Once income crosses the allowance, registration is required by 5 October following the end of the tax year in which it happened. For 2025 to 2026, that means Monday 5 October 2026.
- Clearing out your own wardrobe and selling unwanted belongings is generally not trading, whatever the total.
- Buying items to resell, making things to sell or offering a service for payment is trading from the first pound.
- Marketplaces and gig platforms now pass sales data to HMRC, so an unreported income stream is easier to spot than it was.
What happens if you tell HMRC late
Registering after 5 October is treated as a failure to notify. The penalty is linked to the tax that ends up being due and to how quickly you come forward, so a late but voluntary registration with little tax at stake can attract a reduced or nil charge. Ignoring the obligation altogether is a different matter, and interest runs on unpaid tax from the normal payment date regardless.
The registration itself is only the first step. Once you have a Unique Taxpayer Reference, the return for 2025 to 2026 is due by 31 October 2026 on paper or 31 January 2027 online, and any tax owed must be paid by 31 January 2027. Registering early gives HMRC time to send the reference and activation details, which can take a couple of weeks by post.
A check-list before you register
Registering takes minutes once the paperwork is to hand. Gather your National Insurance number, the date your activity started, a rough total of income for the year and, for property, the address of what you let. Then decide which route applies: sole trader registration for anyone running a business in their own name, a separate form for business partners, and the general Self Assessment route for people with untaxed income who are not trading.
It is also worth thinking about record keeping now rather than in January. Digital bookkeeping is becoming the norm for small businesses in several countries, as the move to electronic invoicing for micro and small enterprises shows, and the UK is heading the same way. Since 6 April 2026, sole traders and landlords with qualifying income above £50,000 have been inside Making Tax Digital for Income Tax, which means quarterly updates sent through compatible software rather than a single annual return. The threshold is set to fall to £30,000 in April 2027 and to £20,000 in April 2028. A side hustle that is small today may not stay small, and habits built early are the cheapest ones.
New sole traders should also look beyond tax. Working for yourself removes the safety nets an employer provides, which is why choosing the right professional insurance belongs on the same to-do list as registration. And if the extra income is starting to rival your salary, it may be time to ask whether the venture deserves more of your week, a question explored by one entrepreneur who halved his working time while doubling his income.
Common misunderstandings
- “I already pay tax through my job, so I do not need to register.” PAYE covers your salary only. Income from a business, a lodger or a rental sits outside it.
- “I made a loss, so there is nothing to declare.” If gross receipts passed £1,000, HMRC still expects a return. Declaring a loss can even be useful later.
- “I can sort it all out in January.” The January date is for filing and paying. Notification has its own, earlier deadline, and that is the one that falls on 5 October.
Frequently asked questions
Does the 5 October deadline apply everywhere in the UK?
Yes. Income tax administration is run by HMRC across England, Scotland, Wales and Northern Ireland. Scottish taxpayers pay different rates and bands on earned income, but the registration and filing deadlines are identical.
I earned £900 from selling crafts. Do I need to do anything?
Not for that activity alone. Gross trading income below £1,000 is covered by the trading allowance and does not need to be reported. Keep a simple note of your sales in case the total grows next year.
I registered years ago but have not filed for a while. Am I still registered?
Not necessarily. If HMRC closed your Self Assessment record because no return was needed for 2024 to 2025, you must tell them again by 5 October. The online service will explain how to reactivate an old record rather than create a new one.
Sources
- GOV.UK – Register for Self Assessment
- ByteStart – What is the £1,000 trading allowance?
- Apex Accountants – Self Assessment registration deadline: what to do before 5 October 2026
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