What happens if I do not register for self-assessment in time?

If you meet the criteria to file a self-assessment tax return for the first time, you must register with HM Revenue & Customs (HMRC) by the deadline. For the 2024/2025 tax year, the deadline to register for self-assessment is 5th October 2025. Where HMRC) is not notified before the deadline, failure to notify penalties may be applied.  

Myrtle Lloyd, HMRC’s Chief Customer Officer, said: “Thousands of people join self-assessment each year and anyone new to self-assessment for the 2024-25 tax year should register as soon as possible. Just search ‘register for self-assessment’ on GOV.UK to access a wide range of resources to help with registering and sign up today.” 

What is a failure to notify penalty? 

Failure to notify penalties are calculated based on the amount of tax you did not pay, as a result of not registering and completing a tax return. 

Failure to notify penalties are based on: 

• the potential tax due and unpaid at the due date – HMRC calls this ‘potential lost revenue’
• whether not notifying HMRC was deliberate or concealed 
• whether you notified HMRC before you had reason to believe it was about to find out ‘unprompted disclosure’. 
• how much assistance you give to HMRC when disclosing your liability to pay tax 

When will HMRC not issue a failure to notify penalty? 

1. HMRC will not charge you a penalty for a failure to notify if you meet the criteria to register for self-assessment but do not owe any tax. However, you may not realise you do owe tax until you file your self-assessment tax return, as the tax return makes some of the calculations for you from the answers you file. It is therefore not a good idea to rely on the assumption that you won’t receive a penalty and ignoring the registration deadline.
    
2. If you are late meeting the registration deadline but do pay all the tax you owe by the 31st January deadline, any failure to notify penalty should be nil, on the basis no tax was owed by the due date. 
    
3. If all the following apply:  

• ​you have a reasonable excuse for the failure
• the failure was not deliberate 
• you told HMRC without unreasonable delay after a reasonable excuse ended 

then HMRC will not issue a failure to notify penalty. 

What happens if I get a failure to notify penalty? 

If you receive a failure to notify penalty, speak to an accountant who can help you understand if it is fair or if there are grounds to appeal.If there are exceptional circumstances, you can appeal against the penalty. The minimum penalty for an ‘unprompted disclosure’ is lower than the minimum penalty for a prompted one. 

The penalty ranges for the various categories which HMRC uses (deliberate, concealed etc) are found here. 

What should you do if you missed the self-assessment registration deadline? 

Register for self-assessment as soon as you can. If you notify HMRC, submit your tax return before the filing deadline (31st January) and pay your tax on time, the potential tax due and unpaid will be zero, therefore no penalty will arise. 

If you register for self-assessment after 5th October, HMRC may confirm that the deadline to submit your tax return is later than 31st January (generally three months from the date of their letter).. In this case, you must be aware that the tax is still due by 31st January. 

For more information, read our guide on how to register for self-assessment. Your accountant can register for you and help you file your self-assessment tax return ahead of the deadline. Make sure you have everything you and your accountant need to file your tax return without delay. 

How can we help? 

TaxAssist Accountants can help you to get your taxes in order. Speak to our team today by calling 01908 978 278 or using our online contact form. 

Last updated 11 Sep 2025 | First published 12 Nov 2024

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This article is intended to inform rather than advise and is based on legislation and practice at the time. Taxpayer’s circumstances do vary and if you feel that the information provided is beneficial it is important that you contact us before implementation. If you take, or do not take action as a result of reading this article, before receiving our written endorsement, we will accept no responsibility for any financial loss incurred.

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