If you’ve earned income outside of your usual PAYE salary during the 2025/26 tax year, you may need to complete a Self Assessment tax return. If you’ve never filed one before, or are registered but did not need to send a tax return last year, there’s an important deadline to be aware of.
The 2025/26 tax year ran from 6th April 2025 to 5th April 2026. If you need to tell HMRC that you need to file a return and haven’t registered for Self Assessment before, you must register by 5th October 2026.
It’s an easy date to overlook, particularly if this is your first year dealing with Self Assessment. So, what exactly do you need to do?
Who needs to register for a Self Assessment tax return?
Not everyone with additional income automatically needs to file a Self Assessment tax return, so it’s worth checking your circumstances first.
You may need to register if, during the 2025/26 tax year, you were self-employed and earned more than £1,000, received rental income, had taxable investment income such as dividends or savings interest, or had other income that wasn’t taxed through PAYE. There are also other circumstances where HMRC may require you to submit a return.
For example, perhaps you started doing freelance work alongside your job, took on your first rental property or began earning income from a side business. It can be easy to think, “it’s only a bit of extra income, I’ll sort it later” but even if it feels relatively small, you should always check whether you need to tell HMRC about it.
If you’re unsure, HMRC has an online checker to help you establish whether you need to file.
What happens when you register?
If you do need to complete a Self Assessment tax return for the first time, you’ll need to register with HMRC for Self Assessment.
Once registered, HMRC will provide you with a Unique Taxpayer Reference (UTR), which you’ll need when completing your return. You’ll also receive the information and access details needed to get set up for online filing.
This is one reason not to leave registration until the last minute. You need time to get everything in place before you can actually start working through your Self Assessment tax return.
There’s no need to wait until January to deal with it. Once you’re registered, you can start preparing your return after the end of the tax year and get a clearer idea of what you may owe.
Already registered? You might still need to take action
If you’ve used Self Assessment before but didn’t need to submit a return for 2024/25, things can be slightly different.
You may need to reactivate your Self Assessment account rather than simply starting a new registration. HMRC warns that failing to reactivate an existing account can delay your return.
It’s another example of why it pays to check what applies to you rather than assuming the process will be the same as last time.
What happens after the 5th October deadline?
Missing the registration deadline doesn’t mean you can simply forget about the return. If you register after 5th October 2026, HMRC will give you a different deadline for submitting your return. However, your tax bill for 2025/26 will still generally need to be paid by 31st January 2027.
Registering late could also result in a penalty, particularly if tax remains unpaid by the payment deadline.
So, if you think you need to file a Self Assessment tax return, it’s much better to get ahead of it now.
How can Accounts & Returns help?
Your first Self Assessment tax return can feel daunting, especially when you’re juggling work, family life, invoices, receipts and everything else that comes with running a business or earning additional income.
At Accounts & Returns, we can help you understand what’s required, make sure you’re registered correctly and support you through the process of preparing and filing your return.
We can also help you understand your tax position, identify allowable expenses and plan ahead for your tax bill, so there are fewer surprises when the payment deadline arrives.
If you need to register for Self Assessment, don’t leave it until 5th October. Get in touch with our expert team and let’s get you on the right track.
