If you need to complete a Self Assessment tax return for the first time for the 2025/26 tax year, you may need to register with HMRC by 5 October 2026. Here’s what you need to know.
If you have started working for yourself, taken on additional income or otherwise found yourself needing to complete a Self Assessment tax return, there is an important date to be aware of.
HMRC’s deadline to register for Self Assessment for the 2025/26 tax year is 5 October 2026.
That date is now getting close, so if you think you may need to complete a tax return and haven’t registered yet, it is worth checking your position now rather than leaving it until January.
Who needs to register for Self Assessment?
There are several reasons why you may need to register.
For example, you may need to register if you:
- have started working for yourself as a sole trader and your gross trading income is more than £1,000
- have become a partner in a business partnership
- have received untaxed income that needs to be reported to HMRC
- have income from property that needs to be declared
- have another reason for needing to complete a Self Assessment tax return.
The £1,000 trading allowance is based on gross income before expenses, rather than your profit after expenses. So if you have started a small business or side business, it is important to look at your total trading income rather than simply what is left after costs.
HMRC has an online checker if you are unsure whether you need to complete a tax return.
What is the 5 October deadline?
If you need to complete a Self Assessment tax return for 2025/26 and you have not submitted a tax return before, you generally need to tell HMRC by 5 October 2026.
The same deadline can apply if you were registered for Self Assessment previously but did not need to submit a return for 2024/25 and now need to submit one for 2025/26.
If you register after the deadline, HMRC may issue a penalty, so it is better not to leave registration until the last minute.
HMRC has made registration easier
There is some good news if you haven’t registered before.
HMRC launched an improved online Self Assessment registration service on 9 September 2026.
The new service includes:
- information that can be pre-populated
- online support during the registration process
- the ability to save your application and return to it later
- confirmation by email or text when registration is complete.
HMRC also says that people using the new service can receive their Unique Taxpayer Reference (UTR) in their online account within 72 hours, rather than waiting for it to arrive by post.
Once you have registered, you can start preparing your tax return.
What happens after you register?
Registering for Self Assessment is only the first step.
You will need to keep accurate records of your income and allowable expenses throughout the tax year so that your tax return can be completed correctly.
For the 2025/26 tax year, the tax year ended on 5 April 2026.
The deadline for submitting an online Self Assessment tax return and paying any tax due is 31 January 2027.
Although January may seem a long way away, getting your records organised now can make the process much easier.
It also means you have more time to understand how much tax you may owe and plan for the payment.
What if I was already registered?
If you have previously been registered for Self Assessment but didn’t submit a tax return for 2024/25, don’t automatically assume that you need to register from scratch.
HMRC says you may need to reactivate your Self Assessment account if you now need to submit a return for 2025/26.
If you’re unsure what you need to do, it is worth checking your HMRC account or getting advice before submitting anything.
What about Making Tax Digital?
There is another important change that sole traders and landlords need to be aware of.
Making Tax Digital for Income Tax is now being introduced in stages.
From 6 April 2026, sole traders and landlords with qualifying income of more than £50,000 based on their 2024/25 tax return need to use Making Tax Digital for Income Tax, unless an exemption applies.
HMRC has also started signing people up from September 2026 where its records show that they need to use the system but have not already signed up.
Making Tax Digital does not mean that Self Assessment has disappeared. You will still need to submit your tax return and pay your tax bill.
It does mean that eligible businesses and landlords need to keep digital records and send quarterly updates using compatible software.
Don’t leave it until January
If you’re new to self-employment or have started receiving additional income, tax and bookkeeping can quickly become confusing.
The important thing is not to panic — but don’t ignore it either.
If you think you need to register for Self Assessment for 2025/26, check your position now and make sure you understand what HMRC expects from you.
Need help with your Self Assessment?
At Mays Accounting Services, I can help with Self Assessment tax returns and the bookkeeping that supports them. If you’re unsure whether you need to register, what records you need to keep or how to prepare your return, get in touch and I’ll be happy to discuss how I can help.
Mays Accounting Services
Bookkeeping, Self Assessment, VAT and support for small businesses and sole traders.