How to file your Self Assessment tax return online, step by step
Filing your 2025/26 tax return before 31 January? Here's a step-by-step guide for sole traders, from finding your UTR to paying what you owe.
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11/4/20264 min read
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How to file your Self Assessment tax return online, step by step
The deadline for filing your 2025/26 tax return online is 11:59pm on 31 January 2027. The paper deadline was 31 October, so if you haven't filed yet, online is now the only option.
Filing online is less daunting than it sounds. Here's how to do it, one step at a time.
Step 1: Check you're registered and find your UTR
You need a Unique Taxpayer Reference (UTR) to file. It's a 10-digit number on letters from HMRC about Self Assessment, and you can also find it in your HMRC online account or the HMRC app.
If this is your first return and you haven't registered yet, do it now. The registration deadline was 5 October, so HMRC will give you a new filing deadline of 3 months from the date on its letter or email. You still need to pay any tax you owe by 31 January 2027. Our post on whether you need to register for Self Assessment explains who has to.
Step 2: Get your sign-in sorted
Most people sign in with a Government Gateway user ID and password. If you're new to HMRC's online services, you may be set up with GOV.UK One Login instead, which uses your email address.
Do this early. If HMRC needs to post you an activation code, it can take several days to arrive, and that's the last thing you want in late January.
Step 3: Gather your figures
Your 2025/26 return covers 6 April 2025 to 5 April 2026. Before you start, have these to hand:
Your total self-employed income (your sales or turnover) for the year
Your allowable business expenses, or decide whether to use the £1,000 trading allowance instead
Your P60 or P45 if you also had a job
Any rental income, bank interest or dividends
Pension contributions and Gift Aid donations, which can reduce your bill
If you're not sure what you can claim, our post on what expenses you can claim as a sole trader is a good place to start.
Step 4: Choose how to file
You have three options:
HMRC's own online service is free. It works well for simple returns, but it won't prompt you about expenses or reliefs you might have missed
GoSimpleTax asks you questions in plain English, shows your tax bill as you go and files direct with HMRC. It's free to try and you only pay when you submit. Use our link to get 15% off
An accountant, through a service like Taxfix, will prepare and file it for you for a fixed fee
Our guide to the best Self Assessment software for sole traders compares these in more detail.
Step 5: Fill in your return
Whichever route you choose, you'll be asked about each type of income you had. As a sole trader, the main section is self-employment. If your turnover was under £90,000, you can usually give your income and expenses as totals rather than splitting them into categories.
Take your time. You can save your return and come back to it, and nothing goes to HMRC until you press submit.
Step 6: Check, then submit
Before you submit, look over the tax calculation. If the number looks very different from what you expected, check your income and expenses figures first. Once you submit, you'll get an on-screen confirmation and a submission reference. Save or screenshot it.
Made a mistake after submitting? You can amend your return online up to 12 months after the 31 January deadline.
Step 7: Pay by 31 January
Any tax you owe for 2025/26 is due by 31 January 2027. You can pay by bank transfer, debit card or through the HMRC app, and you'll need your UTR as the payment reference.
If your bill is £1,000 or more, you may also have to make your first payment on account towards next year at the same time. That's why the January bill can be bigger than expected. Our post on payments on account explains how it works.
What about Making Tax Digital?
Your 2025/26 return is filed in the usual way, even if Making Tax Digital for Income Tax applies to you from April 2026 or April 2027. MTD changes how you report from the 2026/27 tax year onwards. Not sure where you stand? Our MTD checker will tell you in a few quick questions.
At a glance
Online deadline for 2025/26: 11:59pm on 31 January 2027
You need your UTR and your HMRC sign-in
Gather your income, expenses and any other income before you start
File free through HMRC, with software like GoSimpleTax, or through an accountant
Pay what you owe by 31 January 2027, including any first payment on account
Deadlines and rules correct at time of publication. Always check GOV.UK for the current position.
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