by Asim Abbas
11 November 2026 
The SA103 form explained for sole traders
The SA103 form explained for sole traders
If you’re a sole trader, the SA103 pages are where your business income and expenses go on your tax return. Get them right and you pay the correct tax. Get them wrong and you could overpay or face an HMRC enquiry.
- SA103 is the self-employment section of your tax return
- Use the short version (SA103S) if turnover was under £90,000
- Profits are now taxed on a tax-year basis (6 April to 5 April)
- Class 4 National Insurance is worked out from these pages
There are two versions, short and full, and choosing the right one is the first step.
This guide explains which version you need, what goes in each section and the mistakes to avoid on your 2025/26 return.
What is the SA103?
The SA103 is a supplementary page of your Self Assessment return. You complete it if you worked for yourself as a sole trader during the tax year. If you file online, HMRC’s service shows you the right questions automatically.
Short or full: which do you need?
| Use SA103S (short) if | Use SA103F (full) if |
|---|---|
| Turnover was under £90,000 | Turnover was £90,000 or more |
| Your accounts are straightforward | You need to adjust for things like losses brought forward or overlap |
| You use cash basis or simple records | You’re in a partnership changeover or have complex capital allowances |
The £90,000 limit matches the VAT registration threshold. HMRC’s SA103S notes explain each box.
What goes in each section
Business details
Your business name, description, postcode and start date if you began trading in the year.
Income
Your total turnover, meaning all sales before expenses. If your turnover was £1,000 or less, the trading allowance may mean you don’t need to report it at all.
Allowable expenses
Costs you incurred wholly and exclusively for the business, such as stock, phone, insurance, software, travel and professional fees. You can enter a total or break them down by category.
- Simplified expenses let you use flat rates for working from home and vehicle mileage
- You can claim the £1,000 trading allowance instead of expenses, not as well
- Personal costs and fines are never allowable
Your turnover was £38,000 and allowable expenses £6,500, so your profit is £31,500. Income Tax is about £3,786 and Class 4 National Insurance about £1,136, so you’d pay roughly £4,922 if this is your only income.
Self Assessment tax calculator
Enter turnover and expenses to see your tax and NI.
Capital allowances
If you bought equipment, tools or a van, you can usually deduct the full cost in the year you buy it through the Annual Investment Allowance. Cars work differently and depend on CO2 emissions.
Class 4 National Insurance
HMRC works this out from your profit: 6% on profits between £12,570 and £50,270, and 2% above. Class 2 is no longer compulsory, but you can pay it voluntarily to protect your State Pension if your profits are low.
Fixed-fee accountancy support
Transparent monthly packages for sole traders, landlords and limited companies. Fixed fees agreed upfront, VAT included.
Get a fixed-fee quoteCall 0161 531 4179The tax-year basis
Since 2024/25, sole traders are taxed on profits for the tax year itself, not the accounting year that ends in it. If your accounts don’t run to 5 April or 31 March, you’ll need to apportion profits from two sets of accounts. Any transition profit from the change is spread over up to five years.
Cash basis accounting is now the default for most sole traders, which keeps records simpler. Our self-employed accountants can tell you whether accruals would suit you better.
Common mistakes
- Entering profit in the turnover box
- Claiming both the trading allowance and expenses
- Forgetting to apportion part-business costs, such as a phone
- Missing capital allowances on equipment
- Leaving out a second business: each one needs its own SA103
What should I do next?
All sales for 6 April 2025 to 5 April 2026.
Group them by category and keep receipts.
Equipment and vans usually qualify for full relief.
Our sole trader service prepares the SA103 for you.
Frequently Asked Questions
Do I need an SA103 if I earned under £1,000?
Usually not. The £1,000 trading allowance covers gross self-employed income up to that amount, so you may not need to report it at all.
Can I use the short SA103 if I’m VAT registered?
Yes, if your turnover was under £90,000 and your affairs are simple. Many voluntarily registered businesses use the short form.
Do I need a separate SA103 for each business?
Yes. Each self-employed business needs its own pages, with its own income and expenses.
What happened to Class 2 National Insurance?
It’s no longer compulsory for the self-employed. You can still pay voluntarily if your profits are below the small profits threshold, to protect your State Pension.
Can Wingate complete my SA103?
Yes. We prepare your figures and file your full return from £250 including VAT for self-employed clients.
Need help with this? Wingate Accountants offers fixed-fee online accountancy support across the UK. Call 0161 531 4179 or request a quote at wingateaccountants.co.uk.
About the Author
Ali Imran
I’m Ali Imran, an accountant at Wingate Accountants. I help sole traders, landlords and directors get their returns filed early and accurately, without the last-minute panic.
