SA103 (self-employment pages)

Q: What Is the SA103 Form?

The SA103 is the part of your Self Assessment tax return that deals with self-employment income. It’s where you tell HM Revenue & Customs (HMRC): how much your business earned (your income or turnover) what you spent to run your business (your expenses) what profit you made (income minus expenses) HMRC then uses this information to work out how much tax and National Insurance you need to pay.

Q: Who Needs to Use SA103?

You’ll normally need to complete SA103 if: you are self-employed (you run your own business and don’t work just as an employee), and you earn more than £1,000 from self-employment in a tax year (before expenses). This applies whether you’re a full-time business owner or you just have a side hustle alongside employment.

Q: What Do You Need to Fill Out SA103?

Before you start, it helps to gather: records of all your business income (sales, invoices, receipts from customers) records of your business expenses (invoices, bills, receipts) details of any other self-employment you had in the year your basic personal details (name, address, National Insurance number, UTR)

Part of the Taxapedia UK tax glossary by Tax Online.

Understanding the SA103 Form for Self-Employment

Hey there! If you're self-employed in the UK or thinking about starting your own business, you’ll probably come across something called the SA103 form. It might sound a bit scary at first, but don’t worry – this guide will walk you through what it is, who needs it, and what kind of information you’ll be asked for.

What Is the SA103 Form?

The SA103 is the part of your Self Assessment tax return that deals with self-employment income. It’s where you tell HM Revenue & Customs (HMRC):

how much your business earned (your income or turnover)
what you spent to run your business (your expenses)
what profit you made (income minus expenses)

HMRC then uses this information to work out how much tax and National Insurance you need to pay.

Who Needs to Use SA103?

You’ll normally need to complete SA103 if:

you are self-employed (you run your own business and don’t work just as an employee), and
you earn more than £1,000 from self-employment in a tax year (before expenses).

This applies whether you’re a full-time business owner or you just have a side hustle alongside employment.

What Information Does SA103 Ask For?

The SA103 form focuses on three big areas: income, expenses and profit. Here’s a simple overview:

Section	Description
Business Income (Turnover)	All the money your business received from customers during the tax year.
Business Expenses	Costs of running your business – for example stock, materials, advertising, phone, fuel (business use), and other allowable expenses.
Profits	Your income minus your expenses. This is the amount HMRC uses to calculate your tax.

How Do You Work Out Your Profit?

Here’s a simple example of how profit is calculated:

Your Business Income	Your Business Expenses	Your Profit
£20,000	£8,000	£12,000

In this example, if your business brought in £20,000 and you spent £8,000 on genuine business costs, your profit would be £12,000. That £12,000 is what your tax is based on – not the full £20,000.

What Do You Need to Fill Out SA103?

Before you start, it helps to gather:

records of all your business income (sales, invoices, receipts from customers)
records of your business expenses (invoices, bills, receipts)
details of any other self-employment you had in the year
your basic personal details (name, address, National Insurance number, UTR)

How to Fill Out the SA103 – Step by Step

Gather your records: Add up everything your business earned and everything you spent on running it during the tax year (6 April to 5 April).
Enter your income: Put your total business income (turnover) in the income section of SA103.
Add your expenses: List your allowable business expenses in the relevant boxes.
Work out your profit: The form (or tax software) will work out your profit – your income minus your expenses.
Submit it with your tax return: SA103 is part of your overall Self Assessment, which must be filed by the deadline.

Deadlines You Need to Know

The UK tax year runs from 6 April to 5 April the following year.
Online Self Assessment tax returns (including SA103) are usually due by 31 January after the end of the tax year.

Miss the deadline and HMRC can charge penalties, even if you don’t owe very much tax.

Tips for Filling Out SA103

Tip	Description
Keep good records	Save all receipts, invoices and bank statements. It makes filling in SA103 much easier and helps if HMRC ever ask questions.
Use software or tools	Using simple bookkeeping or tax software can help you add things up correctly and avoid mistakes.
Don’t guess	Try not to estimate figures. Use actual amounts from your records wherever possible.
Ask for help if stuck	If you’re unsure about anything, it’s better to get help than to submit something incorrect.

Final Thoughts

The SA103 form is simply the way you tell HMRC about your self-employed income, your expenses, and your profit. It might look a bit overwhelming the first time you see it, but it’s really just a structured way of answering three questions: What did you earn? What did you spend? and What’s left over?

With organised records and a bit of patience, you can complete it confidently. And if you ever feel unsure, getting guidance from a professional or using a clear, step-by-step tax service can make the whole process much easier.