Late Tax Return Notification: What to Do If You Miss the Deadline

Written by Richard Baldwyn ATT, CTA
January 25, 2026

Late January can be stressful if you've suddenly realised you need to file a tax return though haven’t told HMRC. This situation is more common than you think, especially for first-time taxpayers or those returning to Self Assessment after the Christmas break. 

Knowing what action to take to avoid penalties and interest is vital. This guide provides clear tips on late tax return notification to help you navigate this situation quickly and correctly.

Tips on Late Tax Return Notification

When do You Need to Notify HMRC?

In most cases, you must notify HMRC that you are liable to Income Tax or Capital Gains Tax by 5 October following the end of the tax year.

An Example

You make a capital gain from the disposal of cryptocurrency in 2024–25, you had until 5 October 2025 to notify HMRC. As a result, HMRC issues a formal notice to file a tax return.

Your return is due by the later of:

  • 31 January following the end of the tax year, or
  • Three months after HMRC issues the notice to file

Missing the 5 October deadline can trigger penalties. However, taking action quickly can significantly reduce your exposure.

What action should I take if I discover an issue in late January?

If it’s late January and you've missed the notification deadline, do not panic. Instead, act immediately and take the following steps:

  • Firstly, register for Self Assessment online as soon as possible.
  • Calculate your tax liability and pay the tax due by 31 January, even where you haven't yet received a UTR -  see below.
  •  Alternatively, use your National Insurance number if your UTR hasn’t arrived in time.

As a result of paying the correct tax liability by the deadline, you reduce the risk of penalties based on ‘potential lost revenue’.

An overview of how HMRC Charges Penalties 

HMRC applies penalties based on:

  • How late the notification was.
  • Whether your disclosure was prompted or unprompted.
  • Whether the failure was deliberate.

Penalty ranges:

  • 0% where the notification was unprompted and not deliberate.
  • Up to 100% of the tax due for deliberate concealment.

No penalty may be charged if:

  •  You have a reasonable excuse, 
  • The delay was not deliberate.
  • You notified HMRC without unnecessary delay.

What to do Once Registered for Self-Assessment

Once you've registered for Self-Assessment, submit your tax return as soon as practicable. This avoids further penalties for late filing.

The filing deadline then becomes the later of: 31 January following the tax year, or three months after HMRC issues the notice to file.

However any delays beyond these deadlines may result in a £100 fixed penalty or daily penalties after three months. Furthermore HMRC have the power to charge higher tax-geared penalties for longer delays

Special Steps if you've Previously been in Self Assessment

If you've previously been registered in Self Assessment you must reactivate your account.Do not register again. This may delay processing and could lead to incorrect tax calculations.

Therefore, you should reactivate your existing Self Assessment record by calling the Agent Dedicated Line, or completing form SA1. As you’ll already have a Unique Taxpayer Reference (UTR), this step is essential to avoid duplication.

Summary

Discovering in late January that you need to file a tax return can feel overwhelming. However, quick and informed action can prevent unnecessary penalties and interest.

Whether you are new to Self Assessment or returning after a break, following these tips on late tax return notification gives you the best chance of staying compliant and minimising costs.

For more useful information, check out our Ebooks here.

And if you'd like to know how we can help you with all of this, or with anything else, feel free to give us a call on 01202 048696 or email us at [email protected].

Alternatively, please feel free to complete our Business Questionnaire here.

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About the author

Richard Baldwyn ATT CTA

Richard is Co-Founder of The Friendly Accountants and has more than 30 years' experience in tax, including 3 years spent inside HMRC before moving into private practice. He advises individuals and owner-managed businesses on a wide range of UK tax issues, including the tax challenges created by digital platforms and online business models.

Richard has specialised in UK crypto taxation since 2016 and was one of the first UK tax advisers to write publicly about the taxation of cryptoassets. His work includes advising individuals, investors, founders and owner-managed businesses on complex crypto transactions, HMRC disclosures and enquiries, DeFi, NFTs and the tax issues facing businesses operating with digital assets.

He also has first-hand experience of cryptoassets and Web3 projects, combining practical knowledge of how crypto is used with wider UK tax experience.

He particularly enjoys making complex tax transactions easier to understand and helping clients apply tax rules to transactions and technologies that do not always fit neatly within traditional tax categories. More about Richard and the TFA team

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