What Is a Self Assessment Tax Return? Who Files for 2026/27

Tax Queen

Tax Expert @ Pie

6 min read

What Is a Self Assessment Tax Return?

A tax return self assessment is the yearly report you send to HMRC (HM Revenue and Customs, the UK tax authority) to declare income that hasn't already been taxed, such as profits from self-employment or rent from a property. HMRC uses it to work out how much Income Tax and National Insurance you owe. For the 2026-27 tax year, most sole traders, freelancers and landlords earning more than £1,000 from those sources will need to report it, either through the traditional return or through Making Tax Digital.

How Self Assessment Works

If you're employed, your employer takes tax from your wages through PAYE (Pay As You Earn) before you're paid. When you work for yourself, nobody does that for you, so the system relies on you to report your own income, which is where the name comes from. You add up what you earned during the tax year, take off allowable expenses (costs incurred wholly and exclusively for your business), and the tax is worked out on the profit that's left.

The tax year runs from 6 April 2026 to 5 April 2027. Under the traditional system you don't report as you go. Instead, you file afterwards, covering the whole year. Most people get a Personal Allowance, the amount you can earn before paying Income Tax, of £12,570. Self-employed profits above a certain level also attract Class 4 National Insurance, which is worked out on the same return.

What Goes on the Return

The main return, form SA100, covers your personal details and income such as wages, savings interest, dividends and pensions. Extra sections called supplementary pages cover particular kinds of income: SA103 for self-employment, SA104 for partnerships and SA105 for property. If you file online, the right pages appear based on your answers, so you rarely need to know the form numbers. Our guide to filling in a Self Assessment tax return step by step walks through each part in detail.

Who Must File a UK Self Assessment Tax Return

Whether you need to file a UK Self Assessment tax return depends on where your income comes from, not just how much you earn. These are the most common reasons for the 2026-27 tax year.

Sole Traders, Freelancers and Partners

If you're self-employed and your gross income (your takings before expenses) is more than £1,000 in the tax year, you need to register and file. That £1,000 is the trading allowance, a tax-free amount designed for small side income such as occasional freelance work. Partners in a business partnership must file whatever their share of the profit. If you're just starting out, our guide on how to register as self-employed with HMRC explains the process. If you first earn self-employed income in the 2026-27 tax year, you need to register by 5 October 2027.

Landlords

Rental income follows a similar idea. There's a £1,000 property allowance, so if your rental income is above that you'll usually need to tell HMRC, and in most cases that means filing a return. Letting a furnished room in the home you live in can be different. Rent a Room relief lets you earn up to £7,500 a year tax-free, and if you stay under that limit you generally don't need to report it.

Other Reasons You Might Need to File

Self Assessment isn't only for people who work for themselves. You may also need to file if you receive untaxed income such as tips, commission or money from abroad. The same applies if you have to pay the High Income Child Benefit Charge, which claws back some or all of your Child Benefit when you or your partner earn above a set level. Selling assets such as shares or a second home at a profit can also mean reporting capital gains. If HMRC sends you a notice to file, you must do so even if you think you owe nothing.

Who Usually Doesn't Need To

If all your income comes from a job or pension taxed through PAYE and you have nothing else to declare, you usually won't need to file. Small extra amounts can sometimes be collected by adjusting your tax code instead. If you're unsure, HMRC has an online checker that will tell you.

How Making Tax Digital Changes Things in 2026-27

From 6 April 2026, Making Tax Digital for Income Tax begins. It moves record-keeping online and asks for more frequent updates. For the 2026-27 tax year, it applies to sole traders and landlords whose qualifying income (gross self-employment and property income combined) was more than £50,000 in the 2024-25 tax year. The threshold drops to £30,000 from April 2027.

If you're in scope, you keep digital records in compatible software and send four quarterly updates summarising your income and expenses, due by 7 August, 7 November, 7 February and 7 May. You then submit a final declaration by 31 January 2028, confirming your figures and adding any other income. For you, that final declaration replaces the traditional return. Software such as Pie Tax is built to handle this alongside ordinary Self Assessment. If your income is below the threshold, you carry on filing the usual way for now.

Key Deadlines and Payments for 2026-27

For the 2026-27 tax year, the main dates are 5 October 2027 to register if you're new to Self Assessment, 31 October 2027 for paper returns and 31 January 2028 for online returns. Any tax you owe for the year is also due by 31 January 2028.

Missing a deadline costs money. On the traditional system, a late return brings an initial £100 penalty even if you owe no tax, with more added the longer it stays late, and interest is charged on late payments. People in Making Tax Digital move to a points-based system for late submissions, where a penalty applies once you build up enough points.

Payments on Account

Many people are caught out by payments on account, which are advance payments towards the next year's bill. If your bill is £1,000 or more and less than 80% of your tax was collected at source, HMRC usually asks for two payments, each half of the previous year's bill, due on 31 January and 31 July. In your first year this can mean paying a year and a half's tax at once. Our article on when the self-employed pay tax explains the timing, and this guide to budgeting for your Self Assessment tax bill can help you set money aside.

Keeping Records That Make Filing Easier

You need records to back up every figure on your return: sales invoices, receipts for expenses, bank statements and details of any other income. Keep them for at least 5 years after the 31 January filing deadline, so records for 2026-27 should be kept until at least 31 January 2033. Recording income and expenses as you go, rather than in a rush each January, makes the return far quicker. It also helps you spot allowable expenses you might otherwise miss, which is one of the main reasons sole traders move their tax admin into an app.

What to Do Now

Start by checking whether any of the situations above apply to you for 2026-27. If you're new to working for yourself, register before 5 October 2027. If your self-employment and property income was over £50,000 in 2024-25, get ready for Making Tax Digital from April 2026. Then put the filing and payment dates in your diary and set money aside each month.

If you'd like a simpler route, see how Pie Tax helps sole traders, landlords and freelancers with both Self Assessment and Making Tax Digital, pulling in your income and sorting allowable expenses so tax time feels much calmer. When you're ready to give it a go, you can sign in or create your account and start getting your records in order today.