Filing a self assessment tax return in the UK for the 2026/27 tax year is basically just telling HMRC about your income, your gains, and any allowable expenses. HMRC then uses this info to figure out your exact tax bill.
If you work for yourself or you’re a landlord, you will almost certainly have to do one. It might feel like a massive task. But the whole thing is actually pretty straightforward once you know the right steps to take.
This guide explains:
- What is a self assessment tax return,
- Who needs to complete a self assessment tax return,
- How to do a tax return UK,
- And much more…
Let’s get into it!
What Is a Self Assessment Tax Return?
A self assessment tax return is the form you submit to HMRC to declare your income and gains. They take that info to use it to work out exactly what you owe in tax and National Insurance.
It covers income from self‑employment, property, dividends, and foreign income. Basically, if it’s untaxed, it goes on here. It’s also where you claim back your reliefs, allowances, and business expenses. This helps in lowering that final bill.
The main form is called SA100, with supplementary pages for specific income types.
Who Needs to Complete a Self Assessment Tax Return?
If you are asking Do I need to do a tax return UK, the answer is usually “yes” if you fall into any of these categories for the 2026/27 tax year:
- Sole Traders: If you earned more than £1,000 from self-employment before any expenses. Note that if you earn over £50,000, you now have to follow the Making Tax Digital rules.
- High Earners: You generally do not need to file a return for a high salary alone if it’s taxed through PAYE. But you still have to file if you have other untaxed income like dividends or interest. Or if you want to claim back specific tax reliefs.
- Investors: This applies if you got more than £10,000 in dividends. Or if you have a lot of untaxed interest from savings.
- Landlords: If you have income from renting out a property.
- Capital Gains: If you sold something like a second home or shares and made a profit above your £3,000 annual allowance, HMRC needs to know.
Many people find themselves wondering how do i know if i need to do a self assessment tax return when their income is a mix of different things. The quickest way to know is to use the official GOV.UK Self Assessment Tool. You will simply answer a few simple questions about your income. And then it will tell you if a return is required.
The 2026/27 Tax Year: What Has Changed?
This year is actually a huge deal for the UK tax system. The biggest shift is the launch of Making Tax Digital (MTD) for Income Tax. If you are a sole trader or a landlord with a gross income over £50,000, this is for you. Instead of doing one big self assessment tax return at the end of the year, you now have to keep digital records. You also have to send updates to HMRC every three months.
Does MTD Affect My Self-Assessment?
If you hit that £50,000 threshold, your self assessment tax return journey looks different now. You must use HMRC-compatible software. These are used to send a summary of your income and expenses every three months.
MTD Reporting Deadlines for 2026/27:
- 6 April to 5 July: Deadline 7 August 2026
- 6 July to 5 October: Deadline 7 November 2026
- 6 October to 5 January: Deadline 7 February 2027
- 6 January to 5 April: Deadline 7 May 2027
Even with these updates, you still have to file a Final Declaration. The deadline is by 31 January 2028. This replaces the old annual return. It also confirms your final figures for the whole year.
Our specialist MTD accountants can prepare and file all quarterly updates to HMRC on your behalf.
How to Do a Tax Return in the UK: A Step-by-Step Guide
Filing your self-assessment tax return is much easier. Yes, if you tackle it in small stages. Here is how you can complete your self assessment tax return:
Step 1: Register with HMRC
If this is your first time, you must register for Self Assessment by 5 October 2027 for the 2026/27 tax year. HMRC will then send you a 10-digit Unique Taxpayer Reference (UTR). You need to keep this safe because you will need it for every interaction with them.
Step 2: Gather your records
You cannot accurately report what you don’t track. You’ll need:
- P60 or P45 if you also have a job as an employee.
- Records of all business expenses (like equipment, travel, or office costs).
- Bank statements showing interest received.
- Records of any dividends from shares.
- Details of any gift aid donations or pension contributions (these can reduce your tax bill!).
Step 3: Choose your method
While paper returns still exist, most people choose to do a self assessment tax return online. Remember that if you fall under the new Making Tax Digital (MTD) rules, you must use HMRC-compatible software. This is to submit your records. Yes, you won’t be able to use the standard paper form for your quarterly updates.
Step 4: Fill in the sections
The return is split into different “pages.” You’ll fill in the main section. You need to insert your personal details. And then you’ll add “supplementary pages” for income, such as self-employment or property. This is for things like self-employment or property income.
Step 5: Check and submit
Once you have entered everything, the system will show you how to calculate self assessment tax UK. It will give you a projected bill. Make sure to double-check your numbers because even a simple typo can lead to an overpayment or a penalty.
How to Calculate Self Assessment Tax in the UK
Tax is calculated by:
- Adding up all taxable income.
- Deducting allowances (like the personal allowance of £12,570 for 2026/27). Note: This allowance reduces if you earn over £100,000.
- Applying tax bands:
- 20% basic rate up to £50,270.
- 40% higher rate £50,271–£125,140.
- 45% additional rate on income over £125,140.
- Adding Class 4 National Insurance (for the self-employed).
- Subtracting allowable expenses and tax reliefs.
What Happens if I Make a Mistake on My Return?
No worries. You can usually amend your self assessment tax return for up to 12 months. Yes, after the original deadline. Therefore, if you realise you missed an expense or forgot a source of income, just fix it yourself. Instead of waiting for HMRC to find it.
The Bottom Line
A self assessment tax return is not at all something to dread. Once you understand what it is and why you’re doing it, the process becomes far more manageable.
You need to know whether you need to file and register on time. Also, keep good records throughout the year and do not leave it until January. If you are feeling overwhelmed or just want to make sure you are claiming every relief possible, our MTD accountants are here for you.
How Accotax Can Help
If you need help with self assessment tax returns, MTD, or any accounting service, such as bookkeeping, VAT, or year-end accounts, visit Accotax. We offer a range of packages designed to fit your unique needs!
Reach out, get an instant quote, and let us help you stay compliant!
Disclaimer: All the information provided in this article on “How To Do A Self Assessment Tax Return: Complete Guide for 2026/27“, including all the texts and graphics, is general in nature. It does not intend to disregard any of the professional advice.
