There is no law that says a sole trader must use an accountant. You are legally entitled to prepare and submit your own Self Assessment tax return. So the question is not whether you need one legally — it is whether using one makes financial and practical sense for your situation.
The honest answer is: it depends on your circumstances. This guide helps you work out which side of the line you fall on.
When You Probably Do Not Need an Accountant
If all of the following are true, a basic Self Assessment return is genuinely within the reach of most people using HMRC's own free filing service:
Your only income is from one source of self-employment. Your turnover is below the VAT threshold (£90,000). You have straightforward, clearly documented expenses. You have no rental income, dividends, or capital gains. Your bookkeeping is up to date throughout the year. You are comfortable using HMRC's online systems. You are a basic rate taxpayer with a simple financial picture.
HMRC's own Self Assessment system (which is free) can handle this type of return. The government also provides detailed guidance on what to include and how to calculate your liability.
When You Almost Certainly Do Need an Accountant
The situations below are where mistakes are common, deductions are missed, and the cost of professional help is almost always less than the cost of getting it wrong:
Multiple income sources: If you have employment income alongside self-employment, rental income, dividends, or any other taxable income, your return becomes significantly more complex. The interaction between different income types — particularly around tax band calculations, National Insurance, and payment on account — is where errors frequently happen.
CIS deductions: If you work in construction under the Construction Industry Scheme, your CIS deductions from contractors need to be correctly claimed on your Self Assessment return. Getting this wrong means either underclaiming your refund or overpaying tax. Most CIS subcontractors are owed a refund — but only if the return is filed correctly.
Significant expenses: If you have substantial business costs — vehicle use, home office, equipment, professional subscriptions — calculating and claiming the correct amount requires knowledge of HMRC's specific rules. Overclaiming attracts penalties. Underclaiming costs you money.
Higher earnings (approaching or over £50,000): The High Income Child Benefit Charge applies above £60,000. Your personal allowance starts being withdrawn above £100,000. Payments on account become more significant. Pension contributions become more complex. All of these require careful planning.
Making Tax Digital: From April 2026, anyone with self-employment or rental income above £50,000 must use MTD-compatible software and submit quarterly digital returns to HMRC. This is a significant change that most sole traders are not ready for without help.
Business is growing: If your turnover is approaching £90,000 (the VAT threshold), approaching the MTD threshold, or you are considering incorporating as a limited company, you need professional advice before making decisions that have significant tax consequences.
Behind on filings: If you have missed Self Assessment deadlines or have unfiled returns, the process of catching up, calculating penalties, and making appeals is significantly smoother with a professional involved.
What Does an Accountant Actually Save a Sole Trader?
This is where many sole traders underestimate the value of professional advice.
Missed deductions: In a typical review of a new sole trader client's previous return, we find missed deductions of £1,000 to £4,000. Common ones include: home working expenses, vehicle costs calculated incorrectly, capital allowances not claimed on equipment, mobile phone business proportion not claimed, professional subscriptions and training not included.
At a 20% basic rate tax, £3,000 in missed deductions costs you £600 in unnecessary tax. At 40% higher rate, it costs you £1,200.
Planning opportunities: An accountant considers your full financial picture. Should you make a pension contribution this year to reduce your tax bill? Should you bring forward or delay a large purchase to manage your tax liability? Should you change your accounting date? These decisions require professional judgment.
Error prevention: HMRC issues approximately 800,000 compliance checks per year. While the risk of a full enquiry is low, a tax return prepared by a professional is significantly less likely to trigger one than a self-prepared return with errors or inconsistencies.
Time: Sole traders consistently underestimate how long preparing their own Self Assessment takes. Most take 4 to 12 hours to gather records, work through the return, and deal with any queries. At their own hourly rate, that time is often worth significantly more than an accountant's fee.
The Maths for a Typical Sole Trader in 2026
Scenario: A self-employed plumber in Harrow with annual turnover of £55,000, vehicle costs, tools, materials, and a phone.
Self-preparation: No fee. 8 hours of time at £20 per hour implied cost = £160. Likely missed deductions: £2,500. Tax cost of missed deductions at 20%: £500. Total true cost of self-preparation: £660.
Professional accountant: £250 fixed fee. All deductions captured. Return prepared in 2 hours of the client's time (providing documents). Zero HMRC query risk. Total cost: £250.
Net saving from using an accountant: £410 in year one — and the gap grows in future years as the accountant builds knowledge of the business.
A Real-Life Example
Client B came to us after preparing his own Self Assessment for three years as a self-employed electrician. He was confident the returns were correct.
When we reviewed all three years, we found he had never claimed the business proportion of his mobile phone (70% business use on a £40 per month contract), had been claiming a flat mileage rate without recording his business miles properly, and had never claimed the Annual Investment Allowance on two vans he had bought during the period.
The total unclaimed deductions across three years came to £14,200. We submitted amended returns for the two years still within the amendment window. He received a refund of £1,840 from HMRC within six weeks.
Frequently Asked Questions
Need help with your tax position?
At Your Tax Help Accountants in Stanmore, we work with clients across Harrow, Wembley, Edgware and London. Fixed fees, expert advice, no jargon.
Or email info@yourtaxhelp.co.uk | yourtaxhelp.co.uk