Filing a Self Assessment tax return can seem complicated, especially if you are completing one for the first time. However, once you understand who needs to file, what information you need, and how the process works, submitting your tax return becomes much easier.
This guide explains how to file a Self Assessment tax return in the UK , including registration, calculating your taxable income, allowable expenses, payment deadlines, and common mistakes to avoid.
What Is a Self Assessment Tax Return?
A Self Assessment tax return is a way for HM Revenue & Customs (HMRC) to collect Income Tax from people whose income is not fully taxed through PAYE.
You may need to complete a Self Assessment tax return if you are:
- Self-employed as a sole trader and earn more than £1,000 in a tax year
- A partner in a business partnership
- A landlord receiving rental income
- Receiving certain types of untaxed income
- Earning income from investments, dividends, or savings above applicable thresholds
- Receiving foreign income that needs to be reported to HMRC
If you are unsure whether you need to file a tax return , it is important to check your circumstances before the filing deadline.
How to File a Self Assessment Tax Return
The process of filing a Self Assessment tax return can generally be broken down into the following steps.
1. Check if you need to file
Before registering, determine whether you have a Self Assessment tax return requirement .
For example, if you are self-employed and your gross trading income is more than £1,000 during the tax year, you will generally need to register for Self Assessment. Other circumstances, such as receiving rental income or certain investment income, may also create a filing obligation.
If you are uncertain, getting professional advice can help you avoid missing an HMRC filing requirement.
2. Register for Self Assessment
If you are filing a tax return for the first time, you may need to register with HMRC.
You will need to provide relevant personal and business information. After registering, HMRC will provide you with a Unique Taxpayer Reference (UTR) , which you will use when dealing with your Self Assessment tax return.
Make sure your HMRC records are accurate and keep your UTR secure.
3. Gather Your Income Information
Before starting your tax return, collect all the information you need to report your income.
Depending on your circumstances, this could include:
- Self-employment or freelance income
- Employment income
- Rental income
- Pension income
- Bank interest
- Dividend income
- Foreign income
- Other taxable income
Keeping your records organized throughout the year can make the Self Assessment tax return filing process much easier.
4. Calculate Your Allowable Expenses
If you are self-employed, you may be able to deduct certain allowable business expenses from your income when calculating your taxable profit.
Examples may include qualifying costs for:
- Office supplies
- Business travel
- Professional services
- Business insurance
- Advertising and marketing
- Certain equipment and software
- Business use of your home
Only expenses that meet HMRC's rules should be claimed. Keeping receipts, invoices, and other supporting records is important in case HMRC asks for evidence.
5. Complete Your Self Assessment Tax Return
Once you have gathered your information, you can complete your tax return online.
You will need to enter your income, allowable expenses, and other relevant information. HMRC's system will use the information provided to calculate the tax you owe.
Take care when entering figures because mistakes can result in an incorrect tax calculation or require you to amend your return later.
6. Review and Submit Your Tax Return
Before submitting your return, carefully review all the information you have entered.
Check:
- Your personal details
- Income figures
- Business income and expenses
- Tax reliefs and allowances
- Other taxable income
- Bank and payment information
Once you are satisfied that the information is accurate, submit your return online.
When Is the Self Assessment Tax Return Deadline?
For most taxpayers filing online, the deadline for submitting a Self Assessment tax return for the previous tax year is 31 January following the end of the tax year.
The tax year runs from 6 April to 5 April of the following year. For example, income earned during the 2025/26 tax year relates to the tax year ending 5 April 2026.
The deadline for paying the tax you owe is generally also 31 January. Some taxpayers may also need to make a payment on account towards their next tax bill.
It is important to allow enough time to prepare and submit your return rather than waiting until the deadline.
What Happens If You Miss the Deadline?
Missing the Self Assessment deadline can result in penalties and interest.
HMRC can charge an initial late filing penalty, with additional penalties potentially applying if the return remains outstanding for longer. Late payment can also result in interest and penalties.
If you realise you have missed a deadline, submit your tax return and pay any tax due as soon as possible.
Common Self Assessment Tax Return Mistakes
Some common mistakes taxpayers make include:
- Reporting incorrect income
- Forgetting additional sources of income
- Claiming expenses that are not allowable
- Missing the filing deadline
- Failing to keep supporting records
- Incorrectly calculating payments on account
- Entering figures in the wrong section
Using an online Self Assessment tax filing service can help reduce the risk of errors and make the filing process more simple.
File Your Self Assessment Tax Return Online with MyIVA
If you are wondering how to file a Self Assessment tax return and would prefer professional assistance, MyIVA can help.
MyIVA provides online Self Assessment tax return services designed to make tax filing simpler for UK individuals, sole traders, and small business owners. Instead of dealing with complicated tax calculations and paperwork on your own, you can get support with preparing and filing your return online.
From identifying relevant income and expenses to submitting your tax return, professional support can save time and help you stay compliant with HMRC requirements.
Ready to file your Self Assessment tax return? Get started with MyIVA's online tax filing service and make your UK tax return simpler.
