Turned a side hustle into something real this year? Started freelancing, renting out a property, or earning money HMRC doesn’t already tax at source? Then one date matters: 5 October 2026 — the deadline to tell HMRC you need to complete a Self Assessment return for the 2025/26 tax year. Here’s who needs to act, how, and what to do if it’s already slipped by.
What the 5 October deadline actually is
The UK tax year runs from 6 April to 5 April, so this deadline covers the 2025/26 tax year — the one that ended on 5 April 2026. If you need to complete a tax return for that year and you haven’t sent a Self Assessment return before (or you registered in the past but didn’t need to file for 2024/25), HMRC must hear from you by 5 October 2026.
Two things people often blur together:
- Registering — telling HMRC you exist in the Self Assessment system. This is what’s due by 5 October.
- Filing — actually sending your tax return. For 2025/26 that’s due by 31 October 2026 on paper, or 31 January 2027 online, along with any tax you owe.
💡 Insight: registration unlocks everything else. You can’t file a return you were never registered for — so a missed 5 October quietly turns into a missed 31 January, with two sets of problems instead of one.
Who needs to register by 5 October
You’ll typically need to register if the 2025/26 tax year was the first time you:
- Became self-employed as a sole trader — even alongside a day job.
- Earned more than the £1,000 trading allowance from self-employment or a side hustle.
- Received untaxed income, such as rent, commission or tips, above HMRC’s limits.
- Had other income that can’t be collected through your payslips, such as certain savings, investment or property income.
Two useful clarifications. If HMRC has already written to you about a 2025/26 return, you don’t need to register — just file on time. And if your side income is modest, the £1,000 trading allowance can mean there’s nothing to report at all. Unsure? The “Check if you need to send a Self Assessment tax return” tool on GOV.UK settles it in a couple of minutes.
How to register — and why to do it this week
Registration is free and online. You’ll need your National Insurance number and some basic personal details; if you’re self-employed, you’ll follow the sole trader route. Once you’ve registered, HMRC will issue a Unique Taxpayer Reference (UTR) — your permanent ID for all things Self Assessment. You’ll need that, plus a Government Gateway account, to file.
That UTR is why “this week” is the smart answer. It takes HMRC time to issue, and a first-week-of-October registration leaves the clock running against your next deadline. Register now and you’ll glide into autumn with the groundwork done.
One more thing: Making Tax Digital (MTD) for Income Tax is rolling out. If your self-employment and property income is over £50,000, you’ll keep digital records and send quarterly updates through compatible software rather than one annual return — and HMRC is automatically signing up people who qualify. If that’s you, filing goes from yearly to quarterly: one more reason to get organised from day one.
What happens if you miss it
HMRC’s own guidance is clear: if you tell them after 5 October 2026, you could get a penalty. The outcome depends on your circumstances — how much tax is involved, why the deadline was missed and how quickly you put things right.
If that date has passed, don’t hide from it — the worst move is doing nothing and hoping January absorbs the problem. Register as soon as you can, file early and tell HMRC what happened: coming forward voluntarily almost always lands better than waiting for a letter. Genuine reason, such as serious illness? Say so — HMRC can accept “reasonable excuses”.
Other autumn dates to diarise
5 October rarely travels alone. While your diary is open, these are worth noting:
- 7 October — VAT returns and payments are due for the quarter ended 31 August 2026.
- 22 October — electronic PAYE (and CIS) payments are due for the tax month to 5 October; 19 October if you pay by post.
- 31 October — the paper Self Assessment deadline for 2025/26. Online filers get until 31 January 2027.
If several of these apply to you at once, that’s usually the point where a fixed-fee accountant starts paying for itself — more on that in a moment.
Quick answers
What is the 5 October 2026 deadline?
It’s the deadline for telling HMRC you need to complete a tax return for the 2025/26 tax year (6 April 2025 to 5 April 2026), if you haven’t sent a Self Assessment return before, or registered before but didn’t need to file for 2024/25.
Who needs to register for Self Assessment?
Anyone with income HMRC doesn’t already tax at source — typically new sole traders, side-hustle earnings above the £1,000 trading allowance, landlords, and people with untaxed income above HMRC’s limits. If HMRC has already written to you, you don’t need to register again.
What happens if I register late?
HMRC says you could get a penalty if you tell them after 5 October 2026. The sooner you come forward and put things right, the better the outcome usually is — so register as soon as possible and explain your circumstances.
How long does registration take, and when will I get my UTR?
The online registration takes minutes, but HMRC needs time to issue your Unique Taxpayer Reference. Build in a few weeks — another reason not to leave it until the first week of October.
I registered years ago. Do I need to register again?
Not usually. If you registered before but didn’t send a return last year, you may simply need to reactivate your Self Assessment account rather than register from scratch — HMRC will walk you through it.
Getting deadlines off your plate
Deadlines like this are exactly what we take off our clients’ desks. At Taxora Accountancy you get a dedicated personal accountant who tracks your dates, reminds you before they bite and handles the paperwork — all for a fixed monthly fee from £9.99, with unlimited support and advice included.
Whether you’re registering for the first time or untangling a late start, we’ll make it painless. Get in touch today, or view our services to see how we can help.
This article is for general information only and does not constitute financial or tax advice. Tax rules can change, and your circumstances affect what applies to you. Always confirm your position with a qualified accountant or on GOV.UK before acting.