Missed the 5 October Self Assessment registration deadline? What happens next

The short answer: If you missed the 5 October 2026 deadline to register for Self Assessment for 2025/26, register now. HMRC will give you 3 months from its letter to send your return. Your tax is still due by 31 January 2027, and if you pay it all by then, you won't get a "failure to notify" penalty.

So take a breath. You're not the first to miss it, and on its own it doesn't mean a fine. What matters most now is registering quickly and paying on time.

Who had to register by 5 October 2026?

You had to tell HMRC by 5 October 2026 if you need a tax return for 2025/26 (6 April 2025 to 5 April 2026) and you either had never sent one before, or didn't need to send one for 2024/25.

The most common reasons are:

• you were a sole trader and earned more than £1,000 before expenses

• you were a partner in a business partnership

• you had untaxed income, such as rent or tips

That £1,000 line is the trading allowance. The Autumn Budget on 28 October 2026 announced it will rise to £3,000 from 6 April 2027, along with the point at which you have to report trading income. It still needs to be made law, and it doesn't change anything for 2025/26.

Tax treatment depends on the individual circumstances of each client and may be subject to change in future.

Not sure if you're in? HMRC's free tool to check if you need to send a tax return takes a few minutes, and it doesn't send your details to HMRC. Our guide on how to register as a sole trader covers who counts as self-employed.

What happens if I missed the 5 October deadline?

You can still register, and the sooner you do it, the better your position.

Here's what changes when you register after 5 October 2026:

1. HMRC sends you a letter or email with a new deadline for your tax return. It's 3 months from the date on that letter.

2. Your payment deadline doesn't move. You still need to pay the tax you owe by 11:59pm on 31 January 2027.

3. You may get a penalty, but only if you don't pay all your tax by 31 January.

If it helps, you're in big company. More than 640,000 people registered for Self Assessment in the 12 months to 31 March 2026.

Is there a fine for registering for Self Assessment late?

Not automatically. HMRC says that if you register after 5 October and don't pay all your tax bill by 31 January, you may get a failure to notify penalty. Pay in full by then and that penalty doesn't apply.

If some tax is still unpaid, the penalty is worked out on that unpaid amount. HMRC calls it the "potential lost revenue". You'd get the penalty within 12 months after HMRC receives your return.

How big it can be depends on why you were late, and whether you told HMRC before it found out. These ranges come from HMRC's factsheet on failure to notify penalties:

Percentages are of the tax left unpaid because of the late registration. Where you land in a range depends on how much you help HMRC.

That help gets credit. HMRC reduces a penalty for "telling, helping and giving": up to 30% for telling, 40% for helping and 30% for giving access to records. So registering now, before HMRC comes to you, keeps you in the lowest bands.

Can I avoid a penalty with a reasonable excuse?

Yes, possibly. HMRC won't charge a failure to notify penalty if all three of these apply: you had a reasonable excuse, it wasn't deliberate, and you told HMRC without unreasonable delay once the excuse ended.

HMRC's list of what may count as a reasonable excuse includes:

• a partner or close relative died shortly before the deadline

• an unexpected stay in hospital, or a serious illness

• delays linked to a disability or mental illness you have

• you were unaware of, or misunderstood, your legal obligation

• you relied on someone else to do it, and they didn't

Some things won't count, such as not getting a reminder from HMRC, or finding the online system too hard to use. If you do get a penalty and think it's wrong, you can appeal against it.

How do I register for Self Assessment late?

You register late in exactly the same way as on time. Here's the order to do it in:

1. Check you need to. Use HMRC's checker tool if you're unsure.

2. Sign in to your Personal Tax Account. You can create one with your Government Gateway or One Login details, according to HMRC's announcement of the new registration service.

3. Register, or reactivate an old account. If you registered before but didn't send a return last year, you may need to reactivate your account instead. Filing without doing this can delay your return.

4. Wait for your UTR. That's your Unique Taxpayer Reference.

5. Start gathering records: bank statements, invoices and receipts for 6 April 2025 to 5 April 2026.

The online form fills in some of your details for you, and you can save it and come back later.

How long does it take to get a UTR?

If you register online through your Personal Tax Account, HMRC says your UTR arrives in your online account within 72 hours. By post, it usually takes around 15 days, and longer if you live overseas.

Your UTR is a 10-digit number. You'll need it to file your return online, and it's also the start of your payment reference. You can find it again later in your Personal Tax Account or the HMRC app.

Can I still file my tax return by 31 January if I registered late?

Yes. If you get your UTR in time, you can file your 2025/26 return online by 11:59pm on 31 January 2027, like everyone else. Your letter from HMRC sets your formal filing deadline (3 months from its date), but filing earlier means you know your bill sooner.

The tax itself is due by 31 January 2027 either way. If you can't pin down your exact profit in time, HMRC lets you use provisional figures and correct them later.

Missing your own filing deadline brings separate late filing penalties:

• an initial £100

• after 3 months, £10 a day, up to £900

• after 6 months, 5% of the tax due or £300, whichever is more

• after 12 months, another 5% or £300

Example: registering in November, worked through

These figures are made up to show how it works.

Priya started freelancing as a graphic designer in June 2025. She didn't realise she needed to register, so she does it on 10 November 2026 and gets her UTR online a few days later. Her HMRC letter gives her 3 months from its date to file, which takes her into February 2027.

She files in January and her 2025/26 tax bill is £1,200. As it's her first year and the bill is over £1,000, she also owes a first payment on account for 2026/27: half of £1,200, so £600. Our guide to how payments on account work explains this in more detail.

In the second case, if HMRC agrees it wasn't deliberate and she told HMRC herself within 12 months, the range is 0% to 30% of £400. That's between £0 and £120, before any late payment penalties and interest on the £400.

What if I can't pay my tax bill by 31 January?

It helps to talk to HMRC before the bill grows, because penalties and interest build up. Unpaid tax gets late payment penalties of 5% at 30 days, 6 months and 12 months. Interest is charged too, at 7.75% a year since 9 January 2026 (the Bank of England base rate plus 4%).

If your bill is overdue, you may be able to set up a payment plan to pay in monthly instalments. You'll need your UTR, your bank details and a picture of your income and spending. HMRC will expect you to use savings to reduce the debt first.

Once you're up to date, a Budget Payment Plan lets you pay weekly or monthly towards next year's bill. Our guide on how much to set aside for tax can help you pick an amount, and the sole trader tax and deadline planner puts your key dates in one place.

Still got questions?

Will HMRC remind me to register? Don't count on it. HMRC says not getting a reminder doesn't count as a reasonable excuse, so it's up to you to register.

I registered years ago. Do I register again? You may need to reactivate your existing Self Assessment account instead. HMRC's registration service tells you how when you start.

I earned less than £1,000. Do I need to register? Usually not for trading income, but there are exceptions. For example, you need to register if you want to claim Tax-Free Childcare or Maternity Allowance based on your self-employment.

Does the £3,000 trading allowance help me for 2025/26? No. It's due to start on 6 April 2027, so it applies from the 2027/28 tax year onwards.

Can I send a paper return instead? The usual paper deadline for 2025/26 was 31 October 2026. If you register late, check the deadline in the letter or email HMRC sends you.