When Does a Side Hustle Become a Business in HMRC's Eyes?

A side hustle becomes a business in HMRC's eyes when it amounts to trading, judged by the badges of trade, and once gross trading income passes £1,000 in a tax year it must normally be registered and declared through self-assessment. Your activity, not the money involved, decides whether you are trading. For anyone researching side hustle tax UK 2026 rules, that explains why selling old clothes is tax-free while reselling trainers bought for profit is not. Blue Tick Accountants, a Guildford-based UK tax advisory and accountancy practice, regularly helps employees with second incomes work out where they stand. This article covers the trading tests, the £1,000 trading allowance, registration, how the tax is calculated alongside a salary, and Making Tax Digital.

Key Takeaways

• HMRC uses the badges of trade, including profit motive, frequency of sales and how goods were acquired, to decide whether side income is a trade.
• The trading allowance makes the first £1,000 of gross trading income tax-free and unreportable in the 2026/27 tax year.
• Self-employment income over £1,000 before expenses means a self-assessment tax return must be filed.
• Side hustle profit is added to employment income, so it is taxed at 20% up to £50,270 of total income and 40% above that in 2026/27.
• Class 4 National Insurance at 6% applies only where profits from the self-employment itself exceed £12,570.
• Making Tax Digital for Income Tax applies to self-employed and property income above £50,000 from 6 April 2026, falling to £20,000 from April 2028.

How does HMRC decide whether a side hustle is a business?

HMRC decides whether a side hustle is a business by applying the badges of trade, tests drawn from decades of case law, rather than any income threshold. No single badge is decisive.

The badges most relevant to side income are:

• Profit motive: buying or making something with the intention of selling it at a profit.
• Frequency: repeated, regular sales look like trading; a one-off sale usually does not.
• How the item was acquired: goods bought to resell point to trade, while personal possessions sold second-hand do not.
• Supplementary work: repairing, customising or marketing goods to raise their value.

Selling your own unwanted belongings on Vinted or eBay is not trading. Buying items at car boot sales to resell online every weekend almost certainly is. Services follow the same logic: occasional favours for friends are not a business, but advertised tutoring or freelance design is.

Online marketplaces have shared seller data with HMRC under the digital platform reporting rules since 1 January 2024, so second income tax HMRC enquiries increasingly begin with platform data.

What is the £1,000 trading allowance and how does it work?

The trading allowance is a £1,000 annual exemption that makes gross trading income up to £1,000 in a tax year tax-free, with no need to register or report it. It is measured on sales before expenses and covers all your trading activities combined.

Where gross income exceeds £1,000, you either deduct your actual allowable expenses or deduct the flat £1,000 allowance instead, but not both. The flat allowance suits low-cost activities such as tutoring; actual expenses suit side businesses with stock or equipment. Our guide to the expenses a sole trader can deduct explains what counts when actual costs are the better option.

When must you register for side income self-assessment?

You must register for side income self-assessment by 5 October following the end of the tax year in which your gross trading income first exceeded £1,000. A side business started in the 2026/27 tax year, which ends on 5 April 2027, must be registered by 5 October 2027.

The first return and any tax due follow by 31 January 2028. Registration produces a Unique Taxpayer Reference, and the return reports your salary, already taxed through PAYE, alongside the side income. Anyone new to the process can start with the basics of self-assessment.

Missing the deadline does not cancel the liability, and HMRC can charge failure-to-notify penalties based on the tax unpaid.

How is side hustle tax calculated alongside a salary in 2026/27?

Side hustle profit is added on top of your employment income, so it is taxed at your marginal rate. Your salary normally uses the £12,570 personal allowance first, which means most side profits are taxed at 20% or 40% from the first pound. This is the core of second income tax HMRC calculations.

National Insurance works differently. Class 4 contributions at 6% apply only where profits from the self-employment itself exceed £12,570, regardless of salary. Self-employed profits above the small profits threshold of £7,105 earn a State Pension credit without any Class 2 payment.

Worked example: an employee with a weekend side business

Sarah earns a £40,000 salary and sells handmade candles online. In 2026/27 her gross sales are £10,000 and her materials, postage and platform fees total £2,000, giving a profit of £8,000.

Her total income is £48,000, below the £50,270 higher rate threshold, so the £8,000 is taxed at 20%, giving £1,600 of income tax. With trading profit below £12,570, no Class 4 is due. Had she claimed the £1,000 trading allowance instead of actual expenses, her taxable profit would have been £9,000 and her tax £1,800, so actual expenses save her £200.

Does Making Tax Digital apply to side businesses?

Making Tax Digital for Income Tax applies to a side business once your gross self-employment and property income exceeds the threshold, and employment income is ignored in that test. The threshold is £50,000 from 6 April 2026, £30,000 from April 2027 and £20,000 from April 2028.

Most side hustles fall below the threshold and continue to file an annual return by 31 January. A side business with turnover above £20,000 should expect quarterly digital updates from April 2028, so digital records now avoid a rushed switch later. Our article on your first year in business covers record-keeping from day one.

Frequently Asked Questions

Do I have to pay tax on my side hustle in the UK?

You pay tax on a side hustle in the UK when it amounts to trading and gross trading income exceeds £1,000 in the tax year. Below £1,000, the trading allowance covers it. Above £1,000, you must register for self-assessment and pay income tax on the profit at your marginal rate, on top of your salary.

How much can I earn from a side hustle before telling HMRC?

You can earn up to £1,000 of gross trading income in the 2026/27 tax year before telling HMRC, because the trading allowance covers it in full. The limit applies to sales before expenses, not profit, and to all your trading activities combined.

When do I need to register a side hustle with HMRC?

You must register a side hustle with HMRC by 5 October following the end of the tax year in which gross trading income first exceeded £1,000. For a side business starting in the 2026/27 tax year, registration is due by 5 October 2027 and the first return and payment by 31 January 2028.

Does a side hustle count towards Making Tax Digital?

A side hustle counts towards Making Tax Digital for Income Tax because the test uses gross self-employment and property income, ignoring salary. The threshold is £50,000 from 6 April 2026, £30,000 from April 2027 and £20,000 from April 2028. A growing side business should keep digital records early.

How Blue Tick Can Help

Blue Tick Accountants helps employees with second incomes confirm whether they are trading, register on time, and choose between the trading allowance and actual expenses. Head to our website and book a meeting now.

Conclusion

Whether a side hustle is a business depends on what you do, not how much you earn, and the £1,000 trading allowance decides whether HMRC needs to hear about it. Once gross income passes that figure, register by 5 October after the tax year ends, keep records of sales and costs, and compare actual expenses with the flat allowance. Getting side hustle tax right from the first year keeps penalties away and prepares you for Making Tax Digital as the threshold falls.

About the Author

This guide was written by Leon, founder of Blue Tick Accountants, a tax advisory and accountancy practice in Guildford helping self-employed people, employees with side incomes, landlords and limited company owners across the UK. It was last reviewed for the 2026/27 tax year.

This article is intended for general informational purposes only and does not constitute tax, legal, or financial advice. Tax rules are subject to change and their application will depend on your individual circumstances. You should always seek advice from a qualified professional before taking action. Blue Tick Accountants accepts no liability for decisions made on the basis of this content.