Started earning on the side last tax year? If you had income to declare between 6 April 2025 and 5 April 2026, you must tell HMRC by 5 October 2026.
Why does it matter? It's the deadline most people don't know about, and it comes months before 31 January. Here's who it applies to.
On this page · 6 sections
Do you need to register?
You generally need to register if, during the last tax year, you:
- earned more than £1,000 from self-employment or a side hustle (the trading allowance);
- started renting out a property and made more than £1,000 from it;
- had other untaxed income — dividends, capital gains, foreign income, or a chunky bit of savings interest;
- need to file for another reason (higher earner, child benefit charge, and so on).
If nearly all your tax already comes out of a salary through PAYE, you probably don't need to. Not sure which side of the line you're on? Take our free 30-second check — no sign-up needed.
What "registering" actually does
Registering isn't the same as filing. It simply tells HMRC you'll be sending a return, and it gets you a UTR (Unique Taxpayer Reference) — the 10-digit number you need before you can file anything. The return itself isn't due until 31 January. Think of 5 October as putting your hand up, and January as handing the work in. Here's the full how-to-register walkthrough.
Why you shouldn't leave it to the last minute
Your UTR doesn't arrive instantly. HMRC posts it to you, usually within a couple of weeks — and longer around busy periods. You then need to activate your online account before you can actually file. Register in early October and that clock starts fine; register in mid-January and you can find yourself locked out of your own tax return with the deadline days away. Registering early is the single easiest way to take the January panic off the table.
What if you miss 5 October?
First, don't panic — this is where a lot of scaremongering gets it wrong. Missing 5 October is not an automatic fine.
The "failure to notify" penalty HMRC can charge is based on tax paid late — technically, the tax still unpaid at 31 January because you told them late. So if you register as soon as you realise, and pay everything you owe by 31 January, there's usually no penalty at all. The penalty only really bites if you're late on both counts — you didn't tell HMRC and you didn't pay on time.
How to register
You register online at GOV.UK. If you're newly self-employed you'll use the self-employed route; if you have other untaxed income but aren't self-employed, there's a separate form. Either way, HMRC posts out your UTR, you activate your online account, and you're set up to file. Prefer not to wrestle with any of it? We register you and handle the return.
Common questions
What's the deadline to register? 5 October following the tax year you started earning — so 5 October 2026 for 2025/26 income.
Do I definitely need to register? Usually yes if you earned over £1,000 self-employed, started letting a property, or had other untaxed income. Our free check will tell you.
What if I'm late? Not an automatic fine — register promptly and pay by 31 January and there's usually no penalty.
We'll register you and file the lot
New to this? We get you set up with HMRC and file your return for you — from £25 a month.
Practising accountant since 2015 · Certified Xero Advisor · BSc, University of Salford. This guide is general information, not personal tax advice. Rules, thresholds and deadlines can change — always confirm the current position on GOV.UK or ask us to check your situation.