Self Assessment Registration Deadline: What to Do Before 5 October 2026

We’re increasingly asked by clients who started trading during 2025/26: “Do I need to register for Self Assessment?” It’s a question that catches people out because the registration deadline arrives months before the January filing deadline most people know about.

If you became self-employed, started renting out property, or received untaxed income for the first time in the 2025/26 tax year (6 April 2025 to 5 April 2026), you may need to tell HMRC by 5 October 2026. The exact requirement depends on your income and circumstances, so it is worth using HMRC’s Self Assessment checker if you are unsure.

Key Takeaways:

• 5 October 2026 is the deadline to tell HMRC you need to file a Self Assessment return for the 2025/26 tax year
• You must register if you earned more than £1,000 as a sole trader, were a partner in a business partnership, owed Capital Gains Tax, or meet certain other Self Assessment criteria
• Late registration can trigger a “failure to notify” penalty based on tax still unpaid after 31 January 2027
• Online tax return and payment deadline: 31 January 2027
• Paper tax return deadline: 31 October 2026

What is the Self Assessment registration deadline?

The Self Assessment registration deadline is 5 October 2026 for the 2025/26 tax year. This is the date by which you must tell HMRC that you need to complete a tax return if you have never filed one before, or if you registered previously but did not need to send one for the 2024/25 tax year.

This deadline applies specifically to registration, not filing. Your actual tax return is not normally due until 31 January 2027 for online returns or 31 October 2026 for paper returns.

People who need to file for the first time must register for Self Assessment before they can complete their return. HMRC launched an improved individual online registration service in September 2026. Customers using the new service can receive their Unique Taxpayer Reference (UTR) in their online account within 72 hours, although other registration routes may take longer.

Who needs to register for Self Assessment by 5 October 2026?

You must register if, during the 2025/26 tax year (6 April 2025 to 5 April 2026), you need to complete a Self Assessment return and are not already registered.

Situation	Registration Required?
Self-employed sole trader earning more than £1,000 gross	Yes
Partner in a business partnership	Yes
Sold or disposed of an asset and owe Capital Gains Tax	Yes
Liable for the High Income Child Benefit Charge and not paying it through PAYE	Yes
Off-payroll worker repaying a student or postgraduate loan	Yes
Rental income from property or land	Depends on the amount and circumstances
Tips, commission or other untaxed income	May be required
Taxable foreign income as a UK resident	Usually, although exceptions apply

Property income needs particular care. The first £1,000 of qualifying property income may be covered by the property allowance. If your annual rental income is above £1,000 but no more than £2,500, HMRC says you should contact them. You will generally need to report property income through Self Assessment if it exceeds the relevant HMRC thresholds.

If you are unsure whether you need to send a return, use HMRC’s online Self Assessment checker.

If you earned £1,000 or less from self-employment, you will usually not need to register solely because of that income. However, there are exceptions. For example, you may choose to file voluntarily to prove self-employment for certain benefits or to pay voluntary Class 2 National Insurance contributions.

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How do you register for Self Assessment?

You can register for Self Assessment through GOV.UK. The process depends on your circumstances.

Sole traders will generally need details including:

• Your National Insurance number
• Your business start date
• Your business name, or your own name if trading as yourself
• The nature of your business

Partners may also need details of the partnership, including its UTR where one has already been issued.

If you are not self-employed but need to complete Self Assessment because of another source of income or tax liability, you should use the relevant non-self-employed registration route.

Once registered, HMRC issues you a 10-digit UTR number. Under HMRC’s new individual online registration service, this can appear in your online account within 72 hours, allowing you to start preparing your return.

What happens if you miss the 5 October registration deadline?

If you register after 5 October 2026 and do not pay all the tax you owe by 31 January 2027, you may face a “failure to notify” penalty. The penalty is based on the amount of tax left unpaid as a result of the failure to notify.

It is not a fixed fine. The percentage depends on the circumstances, including whether the failure was deliberate and whether you disclosed the issue voluntarily or after HMRC contacted you.

You could also face standard late filing penalties if you miss the filing deadline that applies to you:

Stage	Late Filing Penalty
1 day late	Initial £100
3 months late	£10 per day, up to £900
6 months late	5% of tax due or £300, whichever is greater
12 months late	Further 5% of tax due or £300, whichever is greater

For the 2025/26 Self Assessment return, late payment penalties are generally 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest on the outstanding amount. You can check the current Self Assessment penalty rules on GOV.UK.

The practical risk of registering late is that it delays your ability to complete your return while the payment deadline remains fixed. Even if HMRC gives you a later filing deadline after late registration, any tax due must still generally be paid by 31 January 2027.

What are the full Self Assessment deadlines for 2025/26?

The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. Here is the main deadline schedule:

Deadline	What’s Due
5 October 2026	Register for Self Assessment if required and you have not filed before, or did not need to file for 2024/25
31 October 2026	Paper tax return must reach HMRC
30 December 2026	Online return deadline if you want eligible tax collected through your PAYE tax code
31 January 2027	Online tax return deadline and payment deadline
31 July 2027	Second payment on account, if applicable

One important detail is that if you register after 5 October 2026, HMRC will send you a letter or email with a different filing deadline. This will normally be 3 months from the date of that letter or email. However, you must still pay any tax you owe by 31 January 2027.

If you are eligible and want your Self Assessment bill collected through your PAYE tax code rather than paying it separately, you need to submit your online return by 30 December 2026.

How does the £1,000 trading allowance affect registration?

The £1,000 trading allowance means that if your annual gross trading income is £1,000 or less, you will usually not need to tell HMRC about that income. This is the gross figure before deducting expenses.

There are exceptions, including situations where you choose to complete a return to claim certain reliefs, pay voluntary National Insurance contributions or demonstrate self-employment for qualifying purposes.

If your gross trading income exceeds £1,000, you generally need to register for Self Assessment even if your eventual taxable profit is below the Personal Allowance and no Income Tax is ultimately due.

Worked example: Sarah started selling handmade goods on Etsy in August 2025. By 5 April 2026, her gross trading income was £2,400. Even though her profit after materials and fees might be minimal, she generally needs to register for Self Assessment by 5 October 2026 because her gross trading income exceeds £1,000.

Worked example: James did odd jobs for neighbours and earned £750 between June 2025 and March 2026. His trading income is below the £1,000 allowance, so he will usually not need to register solely because of that income. He may still choose to file voluntarily in certain circumstances.

You can read HMRC’s detailed guidance on the trading and property allowances.

What should you do after registering for Self Assessment?

Once you have your UTR number, the next steps are straightforward:

1. Make sure you can access your HMRC online account and Self Assessment service
2. Gather your records, including income statements, expense receipts, P60 or P45 documents if you also had employment income, interest records, dividend information and rental income details where relevant
3. File your return early. You can submit your 2025/26 return any time after 6 April 2026 and do not have to wait until January
4. Pay your tax bill by 31 January 2027. If you are eligible to have the bill collected through your PAYE tax code, submit your online return by 30 December 2026

Filing early has real advantages. You know your tax bill sooner, which gives you more time to budget for the payment, and you avoid the January rush.

It is also worth checking the top mistakes to avoid on your Self Assessment tax return before submitting.

Frequently Asked Questions

How long does HMRC take to send a UTR number after registration?

HMRC’s improved individual registration service launched in September 2026 allows customers using the new online service to receive their UTR in their online account within 72 hours. Other registration methods, including some agent or postal processes, may take longer.

Can I still file online if I register after 5 October?

Yes. If you register after 5 October 2026, HMRC will normally give you a revised filing deadline of 3 months from the date of its letter or email.

However, the tax payment deadline does not move with it. You must still pay the tax you owe by 31 January 2027 to avoid late payment consequences.

Do I need to register if I only had a small amount of untaxed income?

It depends on the type and amount of income.

If your gross trading income from self-employment is £1,000 or less, you will usually not need to register solely because of that income, although exceptions apply.

Different rules apply to property income, savings, dividends, foreign income and other untaxed income. HMRC’s Self Assessment checker is the safest way to confirm whether you need to file.

How much does an accountant charge for a Self Assessment tax return?

Accountancy fees vary depending on the complexity of the return, the number and type of income sources, and whether additional calculations or tax advice are required.

At Apex Accountants, we provide a fixed-fee quote upfront based on your specific circumstances, so you know the cost before the work begins.

What if I was self-employed for only part of the 2025/26 tax year?

You still generally need to register by 5 October 2026 if your gross self-employment income for the period exceeded £1,000.

Your tax return covers the full tax year from 6 April 2025 to 5 April 2026, but you report the income and expenses relating to the period during which you were trading. Trading for only part of the year does not change the registration deadline.

Do landlords need to register for Self Assessment separately from Making Tax Digital?

Making Tax Digital for Income Tax and Self Assessment registration are related but separate requirements.

The first £1,000 of qualifying property income may be covered by the property allowance. If your rental income exceeds that amount, whether you need to register for Self Assessment depends on your level of income and circumstances. HMRC advises people with property income above £1,000 but up to £2,500 to contact them, while higher amounts may need to be reported through Self Assessment.

Making Tax Digital for Income Tax began applying from 6 April 2026 to qualifying individuals with self-employment and/or property income who meet HMRC’s conditions, including the relevant qualifying-income threshold. MTD changes how qualifying taxpayers keep records and submit information to HMRC, but it does not remove the requirement to submit the relevant annual tax return.

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Call Anytime 0203 883 4777

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How Apex Accountants Can Help

If you are unsure whether you need to register, or you want help getting your Self Assessment right the first time, that is exactly what we do. Our tax services cover support with tax registration, returns, compliance and payment planning.

We can check whether you need to register, handle the process for you, prepare your return and make sure relevant allowances and reliefs are considered so you do not pay more tax than necessary.

Book a consultation and we will talk through your situation and explain what needs to happen and by when.