What Is the 5 October Self Assessment Deadline?

The 5 October deadline applies to people who need to complete a tax return for the tax year from 6 April 2025 to 5 April 2026 and who:

• have not previously submitted a Self Assessment tax return; or
• were registered in the past but did not need to submit a return for the 2024/25 tax year.

You must notify HMRC that you are chargeable to tax, normally by registering for Self Assessment.

If you already submit tax returns each year and remain registered with HMRC, you should not usually need to register again.

Who May Need to Register for Self Assessment?

You may need to register and submit a tax return if, during the 2025/26 tax year, you:

• were self-employed and received more than £1,000 in gross trading income before expenses;
• became a partner in a business partnership;
• received taxable income from renting out property or land;
• received untaxed income from savings, dividends, commissions or other sources;
• received foreign income that needs to be declared in the UK;
• disposed of an asset and need to report or pay Capital Gains Tax;
• need to pay the High Income Child Benefit Charge and it is not being collected through PAYE; or
• have been asked by HMRC to submit a tax return.

This is not an exhaustive list. Whether you need to file will depend on the type and amount of income you received and your individual circumstances.

You can use HMRC’s online checker if you are unsure whether you need to send a return.

What If I Already Have a Unique Taxpayer Reference?

Having a Unique Taxpayer Reference, often called a UTR, does not always mean your Self Assessment record is currently active.

If you have continued submitting returns each year, you should not normally need to register again.

However, if HMRC previously confirmed that you no longer needed to file, you may need to reactivate your Self Assessment record.

You should also check whether HMRC has issued you with a notice requiring a 2025/26 tax return. If it has, you must submit the return unless HMRC formally agrees to withdraw the requirement.

What Information Will I Need to Register?

The information required will depend on why you need to complete a return, but it may include:

• your National Insurance number;
• your full name and current address;
• the date your self-employment began;
• the nature of your business;
• your existing UTR, if you have one; and
• details of the income or circumstances creating the need to file.

HMRC may take time to process the registration and issue the information needed to access Self Assessment online. It is therefore sensible not to leave registration until the final few days.

What Happens After I Register?

Once registered, you can begin preparing your return for the year ended 5 April 2026.

The main deadlines are:

• 5 October 2026: register for Self Assessment where required;
• 31 October 2026: submit a paper tax return;
• 30 December 2026: submit online if you are eligible and want HMRC to consider collecting a small tax liability through your PAYE code; and
• 31 January 2027: submit an online tax return and pay the tax due.

Filing your return early does not mean you must pay the tax immediately. The normal payment deadline remains 31 January 2027, but completing the return sooner tells you exactly how much you need to set aside.

Why Is It Worth Dealing With Your Return Early?

Leaving Self Assessment until January can create unnecessary pressure, particularly if information is missing or the eventual tax bill is higher than expected.

Preparing early gives you time to:

• gather bank interest, dividend and employment information;
• obtain property or business records;
• identify allowable expenses;
• check whether payments on account will be required;
• correct missing or inaccurate information;
• plan for the amount payable; and
• arrange support if your tax affairs are more complicated than expected.

If you are due a repayment, filing earlier may also allow it to be processed sooner.

What If I Miss the 5 October Deadline?

If you realise after 5 October that you should have registered, deal with it as soon as possible rather than waiting until January.

A late notification does not remove your obligation to submit the return or pay the tax. HMRC may consider penalties where the failure to notify results in tax not being paid on time.

The position will depend on the circumstances, the amount involved and whether there was a reasonable excuse, so take advice promptly if the deadline has already passed.

Need help with your Self Assessment?

If you are unsure whether you need to register or would like help preparing your Self Assessment tax return, I can guide you through the process.

At Tunstall Accounting, you will deal directly with me throughout. I can help you understand what needs to be declared, identify the information required and make sure your return is prepared accurately and submitted on time.