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Speedia TeamFiling a Self Assessment tax return can seem complicated, especially if you are completing one for the first time. However, the process becomes easier when you know what information you need, which forms to complete, and when to submit your return.
A Self Assessment tax return provides HM Revenue and Customs (HMRC) with information about your income, allowable expenses, and other relevant details for the tax year. HMRC then uses the information to calculate how much Income Tax and National Insurance you need to pay.
For the 2025/26 tax year, which runs from 6 April 2025 to 5 April 2026, you can file your Self Assessment tax return from 6 April 2026. The online filing deadline is 31 January 2027, while the paper return deadline is 31 October 2026.
The following steps explain how to file a Self Assessment tax return:
Before registering for or starting a Self Assessment tax return, check whether you are required to submit one.
Use HMRC's online Self Assessment checker and provide information about your income and circumstances.
If you are required to file a return and are not already registered, you should register for Self Assessment.
If you are filing for the first time, register with HMRC.
The registration process depends on your circumstances. For example, self-employed individuals register differently from people who need to report property income or other untaxed income.
If you are self-employed, you will generally register as a sole trader. If you need Self Assessment for another reason, such as property or foreign income, a different registration process may apply.
Once registered, HMRC will provide your UTR Number.
Keep your UTR safe, as you may need it when managing your Self Assessment tax affairs and communicating with HMRC.
To file online, sign in to your HMRC online account.
You will need the appropriate login details and information requested by HMRC.
Once inside your account, select the Self Assessment service and choose the relevant tax year.
For the 2026/27 tax year, the return covers income received between 6 April 2026 and 5 April 2027.
Do not start entering figures until you have gathered the necessary records.
Gather and review the following records:
This helps reduce the risk of missing income or claiming expenses incorrectly.
Self-employed individuals generally need to keep business records for at least five years after the 31 January submission deadline for the relevant tax year.
Not everyone completes the same parts of a Self Assessment tax return.
The main tax return is SA100, while supplementary pages may be required depending on your circumstances.
Common Self Assessment Forms
The forms you need to complete depend on your sources of income and personal tax circumstances. You should only complete the supplementary pages that apply to you.
Enter all relevant taxable income for the tax year.
This can include:
Make sure you use figures relating to the correct tax year rather than figures from a different accounting period or calendar year.
If you are self-employed or have other income where you can claim expenses, enter the relevant allowable expenses.
Depending on your circumstances, these may include:
Only claim expenses that are allowable under the relevant tax rules.
You may also need to report tax reliefs, pension contributions or other deductions that apply to your circumstances.
After entering your information, review the tax calculation provided by HMRC or your software.
Check:
Do not simply assume the calculation is correct. Compare the figures with your own records before submitting the return.
Before submitting your return, review every section carefully.
Pay particular attention to:
Even a small mistake can affect your tax bill.
If you are unsure about a particular entry, consider seeking professional advice rather than guessing.
Once you are satisfied that the information is accurate, submit your return online.
HMRC will provide confirmation once your return has been successfully submitted.
Keep the confirmation and a copy of the submitted return for your records.
You can file your return any time after the end of the tax year. You do not need to wait until January.
Submitting your return and paying your tax bill are two separate steps.
Your Self Assessment statement will show the amount you owe, including any payments on account that apply.
The usual payment deadline is 31 January following the end of the tax year.
HMRC offers several payment methods, including:
Allow enough time for your payment to reach HMRC.
First, determine whether you are required to submit a tax return.
You normally need to file if, during the tax year, you:
HMRC provides an online checker to help you determine whether you need to file a return.
Knowing the deadlines is one of the most important parts of filing a tax return correctly.
|
Deadline |
What you need to do |
|
5 October |
Register for Self Assessment if you need to file for 2025/26 and have not previously registered. |
|
31 October |
Paper Self Assessment tax return deadline |
|
31 January |
Online Self Assessment tax return deadline |
|
31 January |
Pay the tax due for 2025/26 and first payment on account, if applicable |
|
31 July |
Pay the second payment on account, if applicable |
You can submit your return earlier than the deadline. Filing early gives you more time to check your figures, understand your tax bill and plan for payment.
Before starting your return, gather all the relevant financial information for the tax year.
You may need:
If you were employed during the tax year, you may need:
If you are self-employed, collect:
If you receive rental income, you may need:
You should also collect information about:
You should keep appropriate records to support the figures included in your return.
If you need to file a return for the first time, you generally need to register with HMRC.
For the 2025/26 tax year, you must tell HMRC by 5 October 2026 if you need to complete a Self Assessment tax return and have not previously registered. . If you registered previously but did not need to file for 2024/25, you may also need to notify HMRC.
Filing a Self Assessment tax return can be complex, particularly if you have multiple income sources, rental income, or business expenses. Speedia can help you prepare and file your tax return accurately and on time.
If you need support with your Self Assessment tax return, contact us to discuss your requirements and get professional assistance.
1. Can I complete a Self Assessment tax return myself?
Yes, you can complete and submit your Self Assessment tax return yourself through your HMRC online account.
2. How difficult is it to fill in a Self Assessment tax return?
It is usually straightforward if you have accurate records, understand the income you need to report, and know which expenses and tax reliefs apply to you.
3. What is the easiest way to file your own tax return?
For most people, the easiest option is to file online through their HMRC account after gathering the relevant income and expense records.
4. Do HMRC check every Self Assessment?
No, HMRC does not check every return individually, but it uses various checks and risk assessments to identify returns that may require further review.
5. What are common Self Assessment mistakes?
Common mistakes include failing to report income, claiming expenses incorrectly, entering incorrect figures, overlooking tax reliefs, and missing filing or payment deadlines.