Do you need to do a self assessment tax return? It sounds like a simple question, but the honest answer is: it depends on your situation, and a lot of people get caught out because they assume someone will tell them if they need to file.

Who Actually Has to File a Self Assessment Tax Return?

The most common reason people need to file is self-employment. According to HMRC, you must send a return if you’re a sole trader earning more than £1,000 in a tax year — that threshold is lower than most people expect. If you freelance on the side, drive for a delivery app at weekends, or do any paid work outside of PAYE employment, that £1,000 limit kicks in quickly.

There are other triggers too. Rental income, dividends, savings interest above your personal allowance, capital gains from selling assets, and the High Income Child Benefit Charge can all mean you need to file a return even if you’re employed and paying tax through PAYE. If you became a partner in a business, received foreign income, or need to claim certain tax reliefs, those are also reasons HMRC will expect a return from you.

The Deadlines You Need to Have in Your Head

The tax year runs from 6 April to 5 April the following year. Once it ends, you have until 31 October to file a paper return or until 31 January to file online. Almost everyone files online these days — HMRC confirmed that 97.25% of returns for the 2024-25 tax year were filed online. The 31 January deadline is also when any tax you owe has to be paid, so it’s a double deadline.

If you’re in the self-employed or landlord bracket and your income is over £50,000, there’s something else coming that you should know about. Making Tax Digital for Income Tax is being introduced in stages from April 2026, which will require you to keep digital records and submit quarterly updates to HMRC instead of just filing once a year. It’s a significant change, and the sooner you understand what it means for you the better.

What Happens If You Miss the Deadline or Don’t File at All?

HMRC issues an automatic £100 penalty for missing the 31 January filing deadline, even if you don’t owe any tax and even if you’ve paid everything you owe on time. That penalty applies the moment you’re one day late. A lot of people don’t realise that — they assume if their tax bill is zero, there’s nothing to worry about.

If you’re still late after three months, HMRC adds £10 per day on top, up to a maximum of £900. At six months, they add another charge of 5% of the tax due or £300, whichever is higher. Late payment of the tax itself also carries its own interest and surcharges on top of all of that. The penalties stack up fast, which is why getting sorted early — even if you’re behind — is always better than waiting.

Should You Do It Yourself or Use an Accountant?

If your tax situation is straightforward — you’re employed, you have one source of income, no investments or rental property, no complicated expenses — then filing yourself through HMRC’s online system is genuinely manageable. The HMRC portal walks you through it step by step. The difficulty is knowing whether your situation is as simple as you think it is.

Where things get complicated is when you have multiple income sources, business expenses to claim, rental income alongside a salary, or you’re a contractor working through a limited company. Missing an allowance or making an error can cost you more than an accountant would have. I work with sole traders, landlords, freelancers and contractors across Scotland and the UK, and the most common thing I hear after someone’s first return is that they wish they’d asked for help sooner.