If you missed the 5 October deadline to register for Self Assessment, the most important thing is to register as soon as possible. In many cases there is no penalty at all, provided you then file your return and pay the tax you owe by 31 January. The longer you leave it, though, the harder it becomes to meet that January deadline, so it pays to act now.
What the 5 October deadline is for
HMRC expects you to tell it by 5 October if you need to complete a tax return for the tax year that ended the previous April. For the 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026, the registration deadline was 5 October 2026. The online return, and payment of any tax due, then follow by 31 January 2027.
You usually need to register if, during the tax year, you:
- Started working for yourself and earned more than the £1,000 trading allowance
- Started letting property with gross rent over the £1,000 property allowance
- Became a partner in a business partnership
- Received income that was not taxed at source, such as significant dividends, savings interest above your allowances or foreign income
- Had to pay the High Income Child Benefit Charge because your adjusted net income went over £60,000 and you, or your partner, received Child Benefit
- Made capital gains that need to be reported and taxed
If you are a company director, you may also need to register depending on your income and how you are paid. Not every director has to file a return, but many do because they receive dividends.
Will I get a penalty?
Missing the registration deadline is technically a “failure to notify”. The penalty for this is not a fixed fine. Instead, it is a percentage of the tax that is still unpaid on 31 January following the end of the tax year, and the percentage depends on why the failure happened and whether you told HMRC before it found out.
In practice, this means:
- If you register late but still file your return and pay all the tax due by 31 January, there is usually no unpaid tax at that date and so no penalty for failing to notify.
- If tax is still unpaid after 31 January, a penalty can be charged. It is lower where the failure was not deliberate and where you came forward voluntarily.
- If HMRC discovers the income before you tell it, the penalty range is higher.
Telling HMRC yourself, as quickly as possible, is therefore always the best approach. It also counts in your favour if HMRC later reviews the position.
What to do now, step by step
- Register with HMRC straight away. If you are self-employed, register as a sole trader online. If you are not self-employed, for example because you only have rental income or untaxed investment income, use the separate registration route for people who are not self-employed. You will need a Government Gateway account.
- Look out for your UTR. HMRC will send you a Unique Taxpayer Reference by post. This can take a few weeks, which is why leaving it until December is risky. You need the UTR before you can file.
- Activate your online account. If you are filing online yourself, HMRC sends a separate activation code by post. If an accountant is filing for you, they will need you to authorise them as your agent.
- Gather your records. Pull together your income and expenses for the tax year, including bank statements, invoices, receipts, rental statements and details of any other income.
- Prepare and file your return before 31 January. Filing earlier gives you certainty about what you owe and time to arrange payment.
- Pay what you owe by 31 January. This is the key date for avoiding a failure to notify penalty, as well as late payment penalties and interest.
If registering now still leaves you short of time, an accountant can usually speed things up by acting as your agent and dealing with HMRC directly.
Other deadlines and penalties to know about
Once you are registered, the normal Self Assessment deadlines and penalties apply.
| What | Deadline or penalty |
|---|---|
| Online tax return | 31 January after the tax year |
| Balancing payment | 31 January after the tax year |
| Payments on account | 31 January and 31 July (if they apply) |
| Return filed late | £100 immediately |
| More than 3 months late | £10 a day, for up to 90 days |
| 6 and 12 months late | Further penalties of 5% of tax due or £300, whichever is greater, at each point |
| Tax paid late | 5% of unpaid tax at 30 days, further penalties later, plus interest |
Watch out for payments on account
If your first year’s tax bill is £1,000 or more, and less than 80% of your tax was collected at source, HMRC will usually ask for payments on account towards the following year. Each is normally 50% of the previous year’s bill. That means on 31 January you may have to pay your 2025/26 bill plus the first payment on account for 2026/27, which can come as a shock. Planning for this now avoids a cash flow problem in the new year.
If you cannot pay in full
If you will not be able to pay everything by 31 January, contact HMRC before the deadline rather than after. HMRC offers Time to Pay arrangements, and Self Assessment debts can often be set up as a payment plan online. Interest still runs on the unpaid amount, but a plan can prevent further penalties.
What if you missed earlier years too?
Sometimes realising you should have registered this year leads to the uncomfortable discovery that you should have registered in earlier years as well. For example, rental income may have started some time ago, or a side business may have grown gradually.
If that applies to you, it is far better to put things right voluntarily. HMRC has disclosure routes for people who need to declare income from earlier years, and penalties are significantly lower when you come forward unprompted. HMRC can usually go back four years, six if it considers you careless and up to 20 if deliberate, so ignoring the problem rarely makes it go away. An accountant can help you work out what is due and make the disclosure properly.
Questions and answers
Is it too late to register for Self Assessment after 5 October?
No. You can and should still register. Late registration on its own does not automatically lead to a penalty, as long as you file and pay by 31 January.
How long does it take to get a UTR?
It usually takes a few weeks for HMRC to post your UTR, and it can take longer at busy times. This is why it is important to register now rather than waiting until close to the January deadline.
I only earn a little from a side business. Do I need to register?
If your gross income from self-employment was £1,000 or less in the tax year, the trading allowance usually means you do not need to register for that income. Above that, you normally do, even if your profit is small.
Do I need to register if my employer already taxes my salary?
Not just because of your salary. You need to register if you also have other income that has not been taxed, such as rent, self-employment, or if you have to pay the High Income Child Benefit Charge.
What if I will not have my UTR by 31 January?
Contact HMRC and keep a record of when you registered. If the delay is caused by HMRC, you may have grounds to appeal a late filing penalty, but you should still pay an estimate of the tax you owe by 31 January.
Can an accountant register me?
An accountant can guide you through registration and, once authorised as your agent, deal with HMRC, prepare your return and file it for you. This often saves time and avoids common mistakes.
How Digivolve can help
We regularly help people who have missed the registration deadline get registered, get their UTR and get their return filed on time. Our late tax return service is designed for exactly this situation, and we also prepare self-employed tax returns and landlord tax returns for clients in Haywards Heath, across Mid Sussex and throughout the UK.
If you are worried about deadlines, earlier years or how much you might owe, book a free consultation and we will help you work out the next steps.
This article is general information for the 2026/27 tax year and is not personal tax advice. Rules can change, so please speak to us about your own situation.