Self assessment for sole traders is one of those things that sounds far more complicated than it is — but if you have just started working for yourself, it is probably the most important tax obligation you now have.

Do I Actually Need to Do Self Assessment as a Sole Trader?

When you were employed, your employer handled your tax through PAYE and it came out of your pay automatically. As a sole trader, that stops. HMRC does not know what you have earned unless you tell them, and self assessment is how you do that.

You need to register for self assessment if your self-employment income is more than £1,000 in a tax year. That is a low threshold, so most people doing any kind of freelance, contracting, or trade work will need to do this. HMRC requires sole traders to report their income and pay any tax owed through the self assessment system — it covers both Income Tax and National Insurance, not Corporation Tax, which is a limited company thing.

What Are the Deadlines and What Happens If You Miss Them?

The UK tax year runs from 6 April one year to 5 April the next. After that, you have until 31 January to file your return online and pay any tax you owe. Paper returns have to be in by 31 October, though 97% of people file online because it gives you three extra months and is generally easier.

If you miss the 31 January deadline, HMRC issues an automatic £100 penalty — even if you do not owe any tax. Penalties then increase the longer it goes unpaid. Missing a deadline is not the end of the world, but it is worth sorting quickly because the fines stack up and there is no benefit in waiting. If you have already missed one, the best thing to do is file as soon as possible.

What Information Do You Actually Need to File?

Before you sit down to do your return, gather your income records first. That means everything you were paid for your self-employed work during the tax year — invoices, bank statements, PayPal records, whatever applies to how you get paid. If you have been keeping your records tidy throughout the year, this part is straightforward. If you have not, it takes longer but it is still doable.

You will also need your expenses — anything you spent that was genuinely for business purposes. On top of that, if you had any other income during the year (employment income, dividends, rental income, savings interest), that needs to go on the return too. HMRC uses supplementary pages for different income types, so a sole trader with self-employment income will typically need to complete the SA103 self-employment section alongside the main return.

What Can Sole Traders Claim as Expenses?

This is the question most people actually care about, and rightly so. As a sole trader, you can claim expenses that were spent wholly and exclusively for your business. That means things like tools and equipment, business mileage, professional subscriptions, home office costs, phone and broadband (the business portion), accountancy fees, and marketing costs.

You cannot claim personal costs and call them business expenses — HMRC takes a dim view of that. But a lot of sole traders miss out on things they are fully entitled to claim, simply because they did not know they could. Getting this right can make a real difference to your tax bill. It is worth reviewing your expenses properly rather than just guessing, which is one of the main ways I help clients when I handle their returns.