How to File a Self Assessment as a Sole Trader [Full Guide]

Filing a Self Assessment tax return is one of the most important responsibilities you have as a sole trader in the UK. It’s how you report your income, claim allowable expenses, and calculate how much tax and National Insurance you owe.

If you’ve never done it before, the process can seem intimidating. Deadlines, forms, expense rules, and calculations all add complexity. But once you understand how Self Assessment works for sole traders, filing your tax return becomes much more manageable.

This guide walks you through everything you need to know, step by step.

Key takeaways

• There is an income threshold for Self Assessment
  You need to file a Self Assessment if your self employed income goes over £1,000 in a tax year. This applies to side hustles, part-time work, and even years when you made a loss. The threshold is based on income before expenses, not profit.
• Making Tax Digital changes the process, not the deadlines
  From April 2026, many sole traders will need to keep digital records and send quarterly updates using approved software. However, you’ll still submit a final declaration and pay tax in January and July, just as you do now.
• Deadlines are strict, and penalties are automatic
  Key dates, such as 5 October for registration and 31 January for filing and payment, are non-negotiable. Missing them can lead to fines and interest, regardless of how much tax you owe.
• Good record keeping is the biggest lever for saving time and stress
  Staying organised throughout the year makes filing faster, reduces errors, and helps you plan for your tax bill in advance. Using a tool that tracks income, expenses, and tax estimates automatically can remove most of the Self Assessment workload and make compliance feel routine rather than overwhelming.

What is Self Assessment?

Self Assessment is the system used by HM Revenue and Customs (HMRC) to collect Income Tax from people whose taxes aren’t automatically deducted.

As a sole trader, you don’t have an employer calculating and paying your taxes through PAYE. Instead, you must report your income and expenses yourself using a Self Assessment tax return.

Your tax return tells HMRC:

• How much money your business earned
• What allowable expenses you claimed
• How much your total profit was
• How much tax and National Insurance you owe

This information is then used to calculate your tax bill.

Making Tax Digital: How Self Assessment is changing

Making Tax Digital (MTD) is a major reform from HMRC designed to modernise how taxes are recorded and reported in the UK.

Instead of relying on annual, manual reporting, MTD shifts Self Assessment toward digital record-keeping and more frequent updates submitted online via approved software.

What MTD means for sole traders

MTD is being expanded to cover Income Tax Self Assessment (MTD for ITSA). When it starts to be applied on April 6, 2026, sole traders will need to:

• Keep digital records of income and expenses
• Use MTD-compatible software
• Send quarterly updates to HMRC
• Submit a final end-of-year declaration

Quarterly updates under MTD are summaries of income and expenses only. You’ll still submit a final end-of-year declaration and pay tax in January, just as you do under Self Assessment today.

When does MTD apply?

MTD for Income Tax is being introduced in phases:

• From 6 April 2026: Sole traders and landlords whose qualifying income was over £50,000 in the 2024–25 tax year will need to follow the MTD rules.
• From 6 April 2027: The requirement extends to those whose qualifying income exceeds £30,000 in the 2025–26 tax year.
• From 6 April 2028: The government plans to lower the qualifying income threshold further to £20,000 for the 2026–27 tax year.

Even if MTD doesn’t yet apply to you, HMRC’s direction is clear: Digital record-keeping is becoming mandatory for most sole traders.

Who needs to file a Self Assessment as a sole trader?

You must file a Self Assessment tax return if you’re registered as a sole trader and your total self employed income exceeds £1,000 during a tax year. This £1,000 threshold is known as the trading allowance.

Keep in mind that the £1,000 threshold applies to your total income, not profit. This means if you earned more than £1,000 in revenue before expenses, you’ll usually need to register and file a return, even if your business is part-time or not yet profitable.

This requirement applies regardless of whether self employment is your main source of income or something you do alongside other work. Many mistakenly assume Self Assessment applies only to full-time business owners, but HMRC requires anyone earning above the self employment threshold to file.

You’ll typically need to file a Self Assessment if you work independently and get paid directly by clients or customers, rather than through the employer’s payroll.

Common examples include:

• Freelancers, such as writers, designers, developers, marketers, and photographers
• Consultants and contractors working with clients on a project basis
• Tradespeople, including electricians, plumbers, decorators, and builders
• Online sellers using platforms like Etsy, eBay, Amazon, or Shopify
• Content creators, influencers, and streamers earning through sponsorships, ads, or brand deals
• Tutors, coaches, and trainers offering private services
• Delivery drivers or ride-share drivers working independently
• Anyone running a small service-based or product-based business

You must file a Self Assessment even if:

• You also have a full-time or part-time job under PAYE
• Your self employment is a side hustle
• You only worked part of the year
• You made a loss rather than a profit
• You’ve already paid some tax through other sources

Self Assessment ensures HMRC can calculate the correct amount of Income Tax and National Insurance based on your total income from all sources.

Self Assessment deadlines you should know

Missing Self Assessment deadlines can result in automatic penalties and interest, so it’s essential to understand exactly when each deadline applies.

Key Self Assessment deadlines are:

• 5 October: Register for Self Assessment
• 31 October: Paper tax return deadline (if you’re filing by post)
• 31 January: Online tax return deadline (if you’re filing online)
• 31 January: Tax payment deadline
• 31 July: Second payment on account (Only applies if payments on account are required)

For example:

• Tax year: 6 April 2024 to 5 April 2025
• Register by: 5 October 2025 (if it’s a first return)
• Online filing deadline: 31 January 2026
• Tax payment deadline: 31 January 2026
• Second payment on account (if required): 31 July 2026

Even under Making Tax Digital, January and July payment deadlines remain unchanged.

What information do you need before filing your sole trader Self Assessment?

Before you start your Self Assessment tax return, it’s important to gather all the relevant financial information. Having everything ready will make the process faster, reduce the risk of mistakes, and ensure you don’t miss any expenses that could lower your tax bill.

If you are within Making Tax Digital for Income Tax, these steps apply to your final end-of-year declaration, which confirms the figures submitted through quarterly updates.

Here’s what you’ll need:

1. Your Unique Taxpayer Reference

Your Unique Taxpayer Reference (UTR) is a 10-digit number issued by HMRC when you register for Self Assessment. This number identifies you in the system and links your tax return to your account.

You can find your UTR:

• In your HMRC online account
• On previous tax returns
• On letters from HMRC

You’ll need your UTR to access and submit your return.

2. Your income records

You must report all business income earned during the tax year.

Make sure you include:

• All payments received from clients or customers
• Bank statements showing business transactions
• Invoices you’ve issued
• Records from payment platforms such as PayPal, Stripe, or other processors

It’s important to report your total income (gross income), not just what you transferred to your personal account.

3. Your business expense records

Allowable business expenses reduce your taxable profit. This makes expense tracking one of the most important parts of Self Assessment.

Common allowable expenses include:

• Office costs, such as stationery and software subscriptions
• Travel costs, including fuel, public transport, and parking for business trips
• Equipment, such as laptops, tools, and business supplies
• Phone and internet costs used for business
• Marketing and advertising expenses
• Professional services, such as accountants or legal support

You should keep receipts, invoices, or digital records as proof of these expenses. HMRC may request evidence if they review your return.

4. Your National Insurance number

Your National Insurance number is required to complete your Self Assessment. It ensures your National Insurance contributions are correctly recorded and linked to your account.

Having these records organised before you begin filing your return will make the process much smoother and help ensure your tax return is accurate.

Step-by-step: How to file your Self Assessment tax return

Once you’ve gathered your information, you can complete your Self Assessment by following these steps:

Step 1: Register for Self Assessment

If this is your first time filing, you must register with HMRC before submitting a tax return.

After registering, you’ll receive:

• Your Unique Taxpayer Reference (UTR)
• Instructions for setting up your online HMRC account

This process can take up to 10 days, so it’s important to register well before the deadline.

You only need to register once. After that, you’ll use the same account every year.

Step 2: Sign in to your HMRC online account

Once registered, log in to your HMRC online account and access your Self Assessment tax return.

The return is divided into sections covering different types of income. As a sole trader, you’ll mainly complete the self employment sections. You don’t need to complete sections that don’t apply to you.

Step 3: Enter your personal and business details

You’ll be asked to confirm basic information, including:

• Your name and address
• Your National Insurance number
• Your business name (if applicable)
• Your business type and description

Some of this information may already be filled in. Always check it carefully and correct anything that’s outdated or incorrect.

Step 4: Report your business income

Next, you’ll enter your total business income for the tax year. This is your gross income, meaning the total amount you earned before deducting expenses.

This includes:

• Paid invoices
• Direct bank transfers
• Online payments
• Cash payments

Step 5: Add your allowable expenses

You’ll then enter your business expenses. Expenses reduce your taxable profit, which directly reduces how much tax you owe.

For example:

• Income: £40,000
• Expenses: £10,000
• Taxable profit: £30,000

You only pay tax on the £30,000 profit, not the full £40,000 income.

Always ensure your expenses are legitimate business costs and keep records to support your claims.

Step 6: Review your tax calculation

Once you enter your income and expenses, HMRC automatically calculates your tax position.

This includes:

• Your taxable profit
• Income Tax owed
• National Insurance contributions
• Your total tax bill

Review these figures carefully to ensure everything is correct. This step helps you understand exactly how much you owe and why.

Step 7: Submit your tax return

Once you’ve reviewed all sections and confirmed the information is accurate, you can submit your return. HMRC will immediately confirm that your submission has been received.

If you later discover an error, you can amend your return.

Step 8: Pay your tax bill

After submitting your return, you must pay any tax owed by the payment deadline, usually 31 January.

You can pay using:

• Bank transfer
• Debit card
• Direct Debit

If your tax bill exceeds a certain amount, HMRC may also require payments on account. These are advance payments toward the following year’s tax bill, helping spread the cost.

Paying on time avoids interest charges and penalties.

How record keeping makes Self Assessment easier

Self Assessment is much simpler when your financial records are accurate and up to date throughout the year.

Many sole traders leave everything until January, then spend hours sorting through bank statements, invoices, and receipts. This can create stress and increase the risk of mistakes and missed expenses.

When you keep your records organised throughout the year, filing your tax return becomes a straightforward process. You’ll already know:

• How much income your business earned
• What expenses you can claim
• What your estimated tax bill looks like

This gives you clarity and control, allowing you to prepare for your tax payment in advance and avoid unpleasant surprises.

How to choose the right automation for Self Assessment

Not all financial tools make Self Assessment easier – many of them require manual input, spreadsheets, or complex setup, which means you’re still doing most of the work yourself.

The most effective tools automate your financial record keeping completely, so your records are created as you work rather than reconstructed later.

When choosing a tool, look for features that:

• Automatically track income and expenses
• Categorise transactions for you
• Store receipts securely
• Show real-time tax estimates
• Combine banking, invoicing, and tax tracking in one place

This kind of automation ensures your financial records are always pristine without constant effort.

How ANNA helps sole traders prepare and file Self Assessment

ANNA is designed specifically for freelancers and sole traders, helping you stay organised and prepared for Self Assessment without manual work. Instead of tracking income, expenses, and receipts yourself, ANNA automatically creates and maintains your financial records in the background as you run your business.

Here’s how ANNA makes Self Assessment easier:

• Automatic transaction tracking: It records every payment you receive and every business expense you make, keeping your financial records complete and accurate without spreadsheets or manual entry.
• Real-time tax estimates: ANNA calculates your tax position in real time, so you always know how much you owe to HMRC and can stay financially prepared throughout the year.
• Smart tax pots: You can set aside a percentage of your income into a dedicated tax pot, helping you build your tax payment gradually and avoid large, unexpected bills.
• Smart invoicing with automatic payment matching: ANNA lets you create, send, and track invoices, and it automatically matches incoming payments to the correct invoices, keeping your income records accurate without manual work.
• Built-in UK business account: ANNA records all incoming and outgoing payments through your UK business account, with cards and transfers fully integrated into your financial records.
• Automated Self Assessment preparation: It maintains accurate, up-to-date financial records throughout the year, so your Self Assessment calculations and filings are prepared without manual spreadsheets or reconstruction.
• Automated reminders and compliance support: ANNA helps you stay on track with deadlines and requirements, so you never miss important tax obligations.
• 24/7 tax support: Expert support is available whenever you need it, so you can get answers and resolve issues quickly.

Because ANNA keeps your records accurate and organised throughout the year, preparing and filing your Self Assessment becomes faster, easier, and far less stressful. Instead of reconstructing your finances at the deadline, everything is already ready when you need it.

So, try ANNA out today, and make Self Assessment as easy as possible.