Self Assessment for Sole Traders Guide UK

A late-night run, a busy site, or a full diary of jobs can make tax paperwork feel like something to deal with later. But leaving it too long is how a straightforward return turns into a rushed January problem. This Self Assessment for sole traders guide sets out what you need to do, what records matter and where the tax bill can catch you out.

Who needs to complete Self Assessment?

If you are working for yourself as a sole trader, HMRC will usually expect a Self Assessment tax return when your gross trading income is more than £1,000 in a tax year. Gross income means the money coming into the business before expenses are deducted.

This applies whether you are a taxi driver, tradesperson, consultant, delivery driver, online seller or any other self-employed worker. You may also need a return if you receive rental income, are in a partnership, have Capital Gains Tax to report, or HMRC has specifically issued you a notice to file.

The £1,000 trading allowance can be useful for occasional side income. If your gross income from self-employment is £1,000 or less, you may not need to register or submit a return solely for that income. It is not a universal exemption, though. Other income or tax circumstances can still mean a return is required.

Register early and know the key dates

Your tax year runs from 6 April to 5 April. For example, income earned between 6 April 2025 and 5 April 2026 belongs on the 2025/26 return.

If this is your first year as a sole trader, you normally need to tell HMRC by 5 October following the end of that tax year. For 2025/26 income, that registration deadline is 5 October 2026. Once registered, HMRC issues your Unique Taxpayer Reference, usually called your UTR, which you need to file.

Most sole traders file online. The online filing and payment deadline is 31 January after the end of the tax year. Using the same example, the 2025/26 online return and any tax due must be dealt with by 31 January 2027. Paper returns have an earlier deadline of 31 October, so online filing is normally the more practical option.

Do not confuse filing with paying. Submitting the return tells HMRC what you owe. Paying late can still result in interest and penalties, even where the return itself was sent on time.

Why the January bill can be bigger than expected

Your January payment may include two amounts: the balancing payment for the tax year just ended and the first payment on account towards the following year. The second payment on account is usually due on 31 July.

Payments on account are advance payments towards Income Tax and, where applicable, Class 4 National Insurance. They are normally based on the previous year's bill and can come as a nasty surprise after a good first year of trading. They do not usually apply where your tax bill is below £1,000, or where more than 80% of the tax was collected at source, but many full-time sole traders will fall within the rules.

If you genuinely expect profits to drop, you can ask to reduce payments on account. Be careful: reducing them without a sound reason can lead to interest if the final bill turns out to be higher.

Keep records that prove the figures

A tax return is only as good as the records behind it. You do not need a shoebox full of fading receipts, but you do need a clear record of sales, business costs and money paid in or out of the business.

For many sole traders, a separate business bank account makes this far easier. It is not a legal requirement for a sole trader, but it stops personal spending and business transactions becoming tangled. Save invoices, receipts, mileage logs, bank statements, CIS deduction statements and records of any cash income. A photo of a receipt is usually fine if it is readable and stored safely.

HMRC generally requires you to keep Self Assessment records for at least five years after the 31 January filing deadline for that tax year. For the 2025/26 return, that means retaining records until at least 31 January 2032. If HMRC asks questions, being able to show how the figures were reached saves time and stress.

Claim expenses properly, not aggressively

You are taxed on profit, not turnover. Profit is what remains after allowable business expenses have been deducted from your income. The basic test is whether a cost was incurred wholly and exclusively for the business.

Common allowable costs include materials and tools, public liability insurance, advertising, accountancy fees, protective clothing, business phone use, travel for work, software subscriptions and a proportion of premises costs where you work from home. A black cab driver might claim relevant vehicle running costs and licensing costs. A subcontractor may claim tools, safety equipment and travel between temporary workplaces. The detail matters, because each trade works differently.

Personal costs cannot simply be put through the business because they are convenient. Ordinary clothing is a familiar example: everyday clothes are not normally allowable, even if you wear them to work. Food on a regular commute is another. If an expense has both business and private use, claim only the business proportion. That is often the sensible approach for mobile phones, broadband, vehicles and home utilities.

For vehicle costs, you may be able to use mileage rates instead of claiming actual running costs. Mileage can be simpler, particularly where a vehicle is used personally as well as for work. Actual costs may produce a larger deduction in some cases, but they demand better records and the method you choose can affect what is available later. It is worth checking before assuming one route is always best.

Cash basis or traditional accounting?

Many unincorporated businesses can use the cash basis, which generally records income when received and expenses when paid. This often suits sole traders because it follows the money moving through the bank rather than invoices that have not yet been settled.

Traditional accounting, sometimes called the accruals basis, records income when invoiced and costs when incurred. It can be more appropriate where stock, work in progress or unpaid invoices are significant. Cash basis is now the default for many eligible sole traders, but it is not automatically the right choice for every business. The right method depends on how you trade and how you want to manage profit from year to year.

CIS deductions are not the final tax position

Construction Industry Scheme deductions are often mistaken for the final tax bill. They are not. If you are a subcontractor, the contractor may deduct tax from your payments, but you still normally need to complete a Self Assessment return showing your income, allowable expenses and the CIS tax deducted.

The deductions are then credited against your final liability. If too much tax has been deducted, a refund may be due. If your profit and other income create a larger overall bill, there may still be tax to pay. Keep every CIS deduction statement and make sure the figures agree with payments received before the return is filed.

Plan for Making Tax Digital

Making Tax Digital for Income Tax is changing how some sole traders and landlords report their income. From April 2026, those with qualifying self-employment and property income above £50,000 are required to use compatible software and submit quarterly updates. The threshold reduces to £30,000 from April 2027 and is expected to reduce further over time.

This does not mean paying tax four times a year under the standard rules. It means keeping digital records and sending quarterly income and expense updates, followed by an end-of-year finalisation. Getting used to regular bookkeeping now is the easiest way to avoid a last-minute change later.

A practical way to stay ahead

Set aside a percentage of every payment you receive into a separate savings account for tax. The right percentage depends on profit, other income and your personal tax position, but building the habit is more valuable than guessing at the last minute. Review your income and costs monthly, not just when the filing deadline appears.

If you are newly self-employed, your income has grown sharply, or CIS deductions and mixed expenses are making the return difficult, getting the figures checked before January can prevent expensive errors. Short And Sons Accountants works with sole traders who need clear answers, proper records and a tax process that fits around earning a living - not the other way round.

A Self Assessment return should be the final step in a year of sensible record-keeping, not a January scramble. Give the paperwork a regular place in your working routine and your tax position becomes far easier to manage.