SA103 Form: Claiming Expenses and Income for Self-Employed Taxpayers

Being self-employed means freedom, flexibility, and a bit more paperwork come tax season. The SA103 form is where all that independence meets HMRC reality: it’s the part of your Self Assessment where you declare your business income and claim the expenses that keep your work running.

Whether you’re using the short version (SA103S) for simpler setups or the full version (SA103F) for larger businesses, getting these details right keeps your income tax, National Insurance contributions, and tax reliefs on track. In other words: fill it in properly, and both HMRC and your accountant will sleep better at night.

What is the SA103 form (and which version should you use)?

The SA103 is the Self Assessment supplementary page for anyone who’s self-employed. It’s where you tell HMRC how much your business earned, what you spent, and how those numbers add up to your taxable profit for the year. In short, it’s the heart of your self-employment section on the SA100 tax return.

There are two versions:

• SA103S (short version): For simpler tax affairs, usually when your turnover is below the VAT threshold and you don’t need to claim complicated expenses or adjustments.
• SA103F (full version): For more detailed returns—think higher turnover, multiple trades, capital allowances, or more complex deductions.

Both forms feed into your main Self Assessment tax return, ensuring HMRC gets the full picture of your business income and expenses alongside any employment or investment income you may have. You can find both versions on GOV.UK, either in your tax forms pack or ready to complete online.

📌 Pro Tip: Not sure which version fits? If your accounts could fit comfortably on a single spreadsheet tab, the short form usually does the job. If you’ve got several tabs, trades, or capital assets, the full version is the safer bet.

Who needs to fill out the SA103?

If you earn money from your own work rather than through an employer, the SA103 is probably part of your tax return. It’s how sole traders, freelancers, and other self-employed people tell HMRC what they’ve earned and spent during the year.

You’ll need to complete an SA103 if you:

• Run your own business as a sole trader or freelancer.
• Earn more than £1,000 a year in self-employed income (the current trading allowance).
• Work in a trade or profession such as gardening, caring, or consultancy.
• Want to claim business expenses or capital allowances.

If you’re a limited company director, you don’t use the SA103 for your company’s profits—those are reported through corporation tax. But you may still need the SA103 if you have any separate self-employed income alongside your director’s salary or dividends.

It’s also worth noting how your basis period and accounting period line up. These determine which tax year your profits fall into, which can be especially important if you’re new to self-employment or changing your business year-end. You’ll find full guidance and examples on the HMRC website and in your Self Assessment tax return forms.

📌 Pro Tip: Don’t leave your first SA103 until January. Filing early gives you time to fix basis-period mix-ups—the most common (and most confusing) mistake new sole traders make.

What counts as self-employment income?

When you’re self-employed, income means more than just cash payments. HMRC expects you to declare everything your business earns during the tax year—whether it’s paid by bank transfer, credit card, or in kind (yes, even that client who paid you in gift vouchers counts).

Your SA103 form should include:

• Income from sales and services.
• Grants or government support received for your business.
• Any non-cash payments, such as goods or services in exchange for your work.
• Capital gains related to your business, like selling assets or equipment.

How you record that income depends on your accounting method:

• Under the cash basis, you record income when it’s actually received and expenses when they’re paid.
• Under traditional (accrual) accounting, you record income when it’s earned, even if you haven’t been paid yet.

Your chosen method affects the basis period—the tax year your profits apply to—and can also influence overlap relief if your accounting dates don’t match the standard tax year. These details might sound technical, but they matter: they determine how much tax you owe and when.

📌 Pro Tip: Keep a clear record of when money actually hits your account versus when invoices are raised. Mixing up cash-basis and traditional accounting is one of the easiest ways to confuse both HMRC and yourself come tax time.

Claiming allowable expenses, capital allowances and tax reliefs

Filling out the SA103 isn’t just about what you earned—it’s also about what you spent to keep your business running. Claiming allowable expenses and reliefs correctly can make a big difference to your final tax bill, reducing your taxable profit without bending any rules.

Common allowable business expenses include:

• Office costs such as stationery, software, and utilities.
• Travel and mileage for business journeys (not commuting).
• Supplies and equipment needed for your trade.
• Marketing and advertising costs.
• Professional fees, such as accountants or membership subscriptions.

If you work from home, you can claim part of your household bills for the space and time you use. Carers, tutors, and market gardeners can also deduct costs specific to their work, such as tools, plants, or materials.

When it comes to bigger purchases—like machinery, vehicles, or computers—these fall under capital allowances rather than day-to-day expenses. They let you claim a portion of the item’s cost over time, although you’ll need to watch for balancing charges if you later sell or dispose of those assets.

For detailed guidance and examples, HMRC’s helpsheets (available through GOV.UK) are invaluable. They walk you through each category and ensure you claim what you’re entitled to—without crossing any lines.

📌 Pro Tip: Keep receipts for everything, even small items. A few forgotten subscriptions or travel claims might not seem much, but over a year they can add up to hundreds of pounds off your taxable profit.

Filling in and submitting the SA103 (and SA103F)

The SA103 looks detailed, but once you know what HMRC is asking for, it’s simply a logical walk through your business finances. Whether you’re using the short or full version, each section builds a complete picture of your income, expenses, and taxable profit.

Step 1: Gather your information.

Collect your business records for the year—sales totals, invoices, expense receipts, and any supporting documents such as bank statements or grant details. You’ll also need your annual turnover figure to decide whether to use the short or full version.

Step 2: Confirm your accounting period.

Enter your accounting period and basis period, which tell HMRC which tax year your profits apply to. These dates are especially important if you’ve recently started or changed your accounting year.

Step 3: Record your business income.

Report your total income from sales, services, or any other business activity. Make sure these figures match your accounts and any grant or non-cash payments received.

Step 4: Add your business expenses.

Enter allowable costs such as office expenses, travel, marketing, and supplies. If you’re claiming capital allowances, include those figures here as well.

Step 5: Declare your National Insurance contributions.

Self-employed taxpayers pay Class 2 and Class 4 NICs through the same Self Assessment process. The SA103 form automatically feeds these details into your main tax return.

Step 6: Finalise your taxable profit.

Once your income and expenses are complete, the form calculates your taxable profit and any overlap relief you can claim. Check everything carefully before submitting.

Step 7: File your return.

Submit the SA103 (and SA103F if applicable) with your SA100 tax return, either online through your HMRC account or by paper before the deadline. Filing online gives instant confirmation and automatic calculations, making it the smoother option for most people.

📌 Pro Tip: Double-check your accounting period before submitting—most errors on the SA103 come from using the wrong dates, which can distort your profit and tax calculation.

Common mistakes (and how to avoid them)

The SA103 isn’t complicated once you understand it—but a few recurring slip-ups can easily throw off your tax calculation or delay your return. Most come down to mixing personal and business finances or overlooking deductions that could legitimately reduce your bill.

Here are the big ones to watch for:

• Missing allowable expenses: Forgetting day-to-day costs like software, phone bills, or travel can mean paying more tax than you should.
• Over-claiming: Including personal or non-business costs (especially on shared credit cards) is a red flag for HMRC.
• Ignoring capital gains: Selling business assets like equipment or tools can trigger a capital gain, which needs to be reported.
• Mismatched accounting and basis periods: Using the wrong dates can shift income into the wrong tax year, causing confusion and corrections.
• Overlooking balancing charges or overlap relief: These adjustments ensure your profits aren’t taxed twice—but they’re easy to miss.
• Skipping role-specific deductions: Carers, tutors, and market gardeners all have unique expense rules that can boost legitimate tax reliefs.

Taking a few minutes to cross-check your figures against your accounts (and last year’s return) will help you spot these before you hit submit.

📌 Pro Tip: Keep one bank account for your business income and expenses. It’s the easiest way to stay organised—and the simplest way to prove what’s genuinely business-related if HMRC ever asks.

Keep your business (and your taxes) in sync

The SA103 might not be the most thrilling part of running your own business, but it’s one of the most important. Getting your income and expenses right means smoother cash flow, fewer surprises from HMRC, and more time to focus on the work you actually enjoy.

If you’d like a second pair of eyes on your numbers—or help deciding whether to file the short or full version—book a free financial review with a tax adviser through Unbiased. They’ll help you claim confidently, plan ahead, and keep your tax return as efficient as your business.

Frequently Asked Questions (FAQ)