The 5 October Tax Deadline Has Passed — What Happens If You Missed It?

And if you're reading this thinking, “Was I supposed to do something?” you're certainly not alone. For some people, 5 October 2026 was an important tax deadline — the date by which they needed to register for Self Assessment if they became liable to file a tax return during the 2025/26 tax year.

That can apply to far more people than simply those who consider themselves “self-employed”. Perhaps you started doing some freelance work alongside your employment. Maybe your side hustle grew more quickly than expected. You started selling online, earning money from content creation, taking on consultancy work or generating additional income in another way.

At some point, what started as a bit of extra income can become something HMRC expects you to declare. And this is where things can get complicated. If your gross trading income is more than £1,000, you may need to register for Self Assessment. But looking only at the money that has landed in your bank account isn't always enough to understand your tax position.

There can be allowable expenses to consider, different types of income to bring together and, depending on your circumstances, other tax implications that aren't immediately obvious. And one of the most common assumptions is: “If HMRC hasn't contacted me, I must be fine.” Not necessarily.

HMRC doesn't automatically know everything about your financial affairs — and it's generally your responsibility to establish whether you need to register and report your income. So what if 5 October has passed and you've only just realised you might have needed to register? Don't ignore it. Don't assume it's too late. And don't rely on a quick internet search to tell you what applies to you.

The first step is to establish exactly what income you've received, when you started earning it and whether the Self Assessment rules apply to your particular circumstances. If you do need to register, dealing with it sooner rather than later is usually far better than allowing the situation to become more complicated.

Tax deadlines can sound straightforward. Your individual tax position often isn't.

That's why at The Tax Faculty, we don't just look at a figure and tell you what to pay. We look at the circumstances behind it, the rules that apply and whether there are factors that could change the outcome. Because sometimes the most important tax question isn't “How much do I owe?” It's “Have I got this right in the first place?”

If you're unsure whether you should have registered for Self Assessment, or you're worried you've missed something, we're happy to help you get to the heart of the issue.

Independent tax advice. Real experience. No judgement. Just clear answers. Contact us today to schedule a free no-obligation consultation.

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5 October has come and gone

Capital Gains Tax Expertise: The Tax Faculty LLP Managing Partner Charles Tateson Named UK Capital Gains Tax Advisor of the Year

The Finance Monthly Taxation Awards recognises the achievements of tax professionals from around the globe.

Winning such an award is no small feat. It is a reflection of hard work, extensive knowledge, and an ability to navigate the intricacies of the UK tax system.

Read more about Charles and the award here.

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