If you have income from different sources or have recently started working for yourself, it’s important to know whether you need to complete a Self Assessment tax return. Doing so helps you avoid fines and ensures you pay the right amount of tax.
The UK tax year runs from 6 April to 5 April the following year. For example, for the 2024-25 tax year, the deadline to register for Self Assessment is 5 October 2025. Paper tax returns must be filed by 31 October 2025, and online returns by 31 January 2026.
This blog will explain who needs to complete a Self Assessment, why it might apply to you, and how to do self assessment online step by step, making it easier to manage your tax responsibilities.
A self-assessment tax return is a way for HM Revenue & Customs (HMRC) to collect information about the income you have received in the tax year that has not been taxed at source.
The process helps HMRC calculate the tax you owe or determine if you have paid too much and are due a refund.
Many people think, Do I need to complete a self assessment? It depends on your personal financial circumstances.
Here are some common reasons why you might need to complete a self-assessment tax return:
If you have any of the above, then you will most likely need to complete a self assessment tax return. Additionally, HMRC might send you a notice to file a return even if you don’t think you need to.
The UK government website provides an easy online tool to check if you need to send a tax return. You can answer a series of questions about your income and circumstances.
This helps clarify if you need to complete a self-assessment. It is recommended to check this early in the tax year (which runs from 6 April to 5 April) so you can prepare accordingly.
The tax year runs from 6 April to 5 April the following year. If you need to complete a self-assessment, the deadlines are:
Missing deadlines can lead to penalties, so it is important to file on time.
You can make your Self Assessment tax return either online or by post. Online filing is quicker, secure, and gives immediate calculations.
To file your Self Assessment tax return online, you need to first register with HMRC to obtain your Unique Taxpayer Reference (UTR) and your Government Gateway account. Use these to log into HMRC’s online service. On completing your submission, you will receive instant feedback.
If you wish to submit a paper return, you can download or request a paper form from HMRC. You will then prepare your return in a paper diary, as requested, and within the deadline prescribed. Remember that paper returns are due before online filing returns.
If you want to know more about Self Assessment Registration, read this: Self Assessment Registration
If you don’t complete a Self Assessment tax return when you are required to, you could face several penalties from HMRC.
Here are the penalties for not completing a Self Assessment tax return on time:
Delay in Filing or Payment |
Amount / Rate |
Return late (immediately) |
£100 |
3 months late |
£10 per day, max £900 |
6 months late |
£300 or 5% of tax due (whichever is higher) |
12 months late |
£300 or 5% of tax due (whichever is higher) |
Tax payment is late (30 days overdue) |
5% of unpaid tax |
Tax payment is late (6 months overdue) |
5% of unpaid tax |
Tax payment is late (12 months overdue) |
5% of unpaid tax |
Understanding whether you need to complete a Self Assessment tax return is important to managing your taxes smoothly. If you fall into the categories that require filing, taking simple steps to register, gather your income details, and submit your return on time will help you avoid any trouble with HMRC.
If you are a sole trader or self-employed and want to do your Self Assessment, PHS Associates is here to help. Our expert accountants assist you with registration and filing your tax return accurately and on time.
We handle the entire process smoothly so you can focus on growing your business without worrying about tax rules. Trust our professional team to guide you through every step, from signing up with HMRC to submitting your Self Assessment. Contact us at 0208 8611685 and email us at info@phs-uk.co.uk.
You must register for Self Assessment by 5 October after the tax year ends. Paper tax returns are due by 31 October, and online returns by 31 January. Payments for any tax owed also must be made by 31 January. Filing late can lead to automatic penalties, so meeting these deadlines is important.