Do You Need to Register for Self Assessment by 5 October?

October brings an important tax deadline that is easy to overlook.

If you need to complete a Self Assessment tax return for the 2025/26 tax year and you are new to Self Assessment, you generally need to tell HMRC by:

5 October 2026

The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. HMRC says the 5 October deadline also applies in certain cases where you were registered previously but did not need to send a return for 2024/25. GOV.UK

This is not the deadline for submitting your online tax return or paying your tax.

It is the deadline for telling HMRC that you need to enter Self Assessment in the first place.

So, do you actually need to register?

What is Self Assessment?

Self Assessment is HMRC’s system for collecting Income Tax that has not necessarily been collected automatically.

For many employees, Income Tax is deducted through PAYE before their salary reaches their bank account.

But PAYE cannot deal automatically with every type of income.

You may therefore need to tell HMRC about income from sources such as:

• Self-employment
• Property
• Investments
• Foreign income
• Other untaxed income

You report the relevant information through a Self Assessment tax return.

HMRC then uses the information provided to calculate your tax position. GOV.UK

Who needs to register by 5 October 2026?

The deadline is particularly important if you need to file for 2025/26 and:

• You have never sent a Self Assessment tax return before
• You were registered previously but did not need to send a return for 2024/25

If you fall into one of these categories, HMRC says you must tell them by 5 October 2026. GOV.UK

If you have previously used Self Assessment but did not file last year, you may need to reactivate your existing account rather than creating an entirely new registration. GOV.UK

Do sole traders need to register?

This is one of the most common reasons someone becomes responsible for Self Assessment.

HMRC says you must send a tax return if you were self-employed as a sole trader and earned more than £1,000 before deducting expenses during the tax year. GOV.UK

For example, suppose you started freelancing during 2025/26 and received:

£8,000 from customers

with:

£2,000 of business expenses.

Your profit might be £6,000, but your gross trading income was £8,000.

You should therefore check your Self Assessment obligations.

What about a small side hustle?

A side hustle can count too.

It does not need to be your main job.

For example, you might earn additional money through:

• Freelancing
• Photography
• Tutoring
• Consulting
• Gardening
• Content creation
• Online services
• Selling goods as a business

If your gross trading income exceeded £1,000 during 2025/26, you may need to complete a tax return. GOV.UK

This can apply even if you already have a full-time PAYE job.

Your employer dealing with your salary tax does not automatically deal with separate self-employed income.

Does selling things online mean you need Self Assessment?

Not automatically.

There is an important difference between occasionally selling your own unwanted possessions and trading.

For example, selling your old clothes or furniture does not automatically mean you have started a business.

But regularly buying or producing items with the intention of selling them for profit can create a different position.

If you have generated income through platforms or marketplaces during 2025/26, establish what the activity actually represents rather than assuming all online sales are taxable — or that none of them are.

HMRC specifically advises people with additional income from activities such as selling online to check whether they need to tell HMRC. GOV.UK

What if you receive rental income?

Property income is another common reason for needing Self Assessment.

HMRC lists money from renting out property or land as one form of untaxed income that may require a tax return. GOV.UK

This could potentially include income from:

• Buy-to-let property
• A second property
• Holiday accommodation
• Renting land
• Certain short-term letting arrangements

Allowances and specific property rules can affect whether tax is actually due.

But do not assume that because no tax has been deducted automatically, HMRC already knows everything it needs to know.

What if you receive dividends or savings interest?

Some people may need a tax return because of untaxed investment income.

HMRC identifies:

• Savings interest
• Dividends

among the types of untaxed income that can create a requirement to send a return depending on the circumstances. GOV.UK

Whether Self Assessment is actually required depends on the amounts involved and your wider tax position.

This is particularly worth checking if your investment income increased substantially during 2025/26.

What about foreign income?

Foreign income can also create UK reporting requirements.

Examples might include:

• Overseas savings interest
• Foreign dividends
• Overseas rental income
• Certain foreign pensions
• Other overseas income

HMRC lists foreign income as another potential reason for needing a Self Assessment return. GOV.UK

International tax can become significantly more complicated because your residence position, source of income and foreign taxes paid may all matter.

If substantial overseas income is involved, it is sensible to establish the position before the deadline rather than guessing.

What about Capital Gains Tax?

Selling an asset for more than you paid for it can sometimes create a taxable capital gain.

HMRC says a Self Assessment return is required where you had to pay Capital Gains Tax when you sold or disposed of something that increased in value. GOV.UK

Potential examples include gains involving:

• Shares
• Investment funds
• Cryptocurrency
• Second properties
• Other chargeable assets

Capital Gains Tax also has separate reporting rules in some circumstances, so do not assume Self Assessment is always the only deadline that matters.

What about Child Benefit?

The High Income Child Benefit Charge can also create a tax obligation.

HMRC currently lists people who need to pay the High Income Child Benefit Charge and are not paying it through PAYE among those who must send a Self Assessment return. GOV.UK

The interaction between PAYE and Self Assessment has changed over time, so check how the charge is being dealt with in your particular case rather than automatically assuming a tax return is required.

Do company directors automatically need Self Assessment?

No.

Being a limited-company director does not by itself automatically mean you need to submit a Self Assessment return.

However, directors often have other circumstances that can create a requirement.

For example:

• Untaxed income
• Significant investment income
• Capital gains
• Property income
• Foreign income
• Self-employed income outside the company

The relevant question is not simply:

“Am I a director?”

It is:

“Does my overall tax position require a return?”

What if all your income is PAYE?

You may not need Self Assessment.

If you are an employee and all relevant tax has been dealt with correctly through PAYE, there may be no reason to register.

However, you should still check if you also have:

• Rental income
• Self-employed income
• Foreign income
• Capital gains
• Investment income
• Other untaxed income

A PAYE job does not prevent you from needing Self Assessment for something else.

How do you check whether you need a tax return?

HMRC provides an online checker specifically for this.

For October 2026, the checker covers whether you need to send a return for the 2025/26 tax year. GOV.UK

This is a useful first step if your circumstances are straightforward.

If your position involves several income sources, property, a company or significant investments, professional advice may be appropriate.

How do you register?

HMRC launched an improved online Self Assessment registration service in September 2026.

People who are new to Self Assessment can now register through their Personal Tax Account using the updated process. HMRC reported that more than 640,000 customers registered for Self Assessment in the 12 months to 31 March 2026. GOV.UK

Once registered, you will need your Unique Taxpayer Reference (UTR) to submit your return. GOV.UK

Do not leave registration until January when you are trying to file the return itself.

What if you have registered before?

You might not need to start again.

If you were previously registered for Self Assessment but did not submit a return last year, HMRC says you may need to reactivate your Self Assessment account. GOV.UK

Using the correct process matters because HMRC warns that filing without reactivating an existing account can delay the return. GOV.UK

What happens if you miss 5 October?

Do not ignore it.

Register as soon as you realise.

HMRC says that if you register after 5 October 2026, it will send you a letter or email giving you a filing deadline that is three months from the date of that communication.

However, the tax you owe must still be paid by 11:59pm on 31 January 2027. GOV.UK

HMRC also states that if you register after 5 October and do not pay all the tax due by 31 January, you may receive a failure-to-notify penalty. GOV.UK

Missing 5 October therefore does not mean you should wait until next year.

Act as soon as possible.

Is 5 October the tax-return deadline?

No.

There are several Self Assessment dates and they are easy to confuse.

For the 2025/26 tax year:

HMRC confirms these current deadlines for the 2025/26 return. GOV.UK

You do not need to wait until January to file

Once you are registered and have the necessary information, you can submit your return before January.

HMRC allows 2025/26 returns to be submitted any time from 6 April 2026 up to the relevant deadline. GOV.UK

Filing earlier can give you more time to:

• Understand what you owe
• Check the calculation
• Correct missing information
• Plan your cashflow
• Budget for the January payment

HMRC itself encourages earlier filing because it means you know what you owe sooner. GOV.UK

Start gathering your records now

Registration is only the first stage.

Depending on your circumstances, you might need records including:

• P60s and P45s
• Self-employment income
• Business expenses
• Bank statements
• Property income and expenses
• Dividend information
• Savings interest
• Pension contributions
• Gift Aid donations
• Capital gains information
• Foreign income records

HMRC requires taxpayers to keep records such as bank statements and receipts so their returns can be completed accurately. GOV.UK

Starting this in October is considerably easier than trying to find everything at the end of January.

What if you registered but no longer need a return?

Do not simply ignore Self Assessment.

If you believe you no longer need to submit a tax return, HMRC says you should tell them as soon as possible.

Examples could include situations where you:

• Stopped being self-employed
• Stopped receiving property income
• No longer need to deal with the High Income Child Benefit Charge through Self Assessment

HMRC needs to confirm whether the return is still required. GOV.UK

Frequently Asked Questions

When is the Self Assessment registration deadline for 2026?

If you need to complete a return for 2025/26 and the registration requirement applies to you, you must tell HMRC by 5 October 2026. GOV.UK

Is 5 October the deadline for submitting my tax return?

No. The online filing deadline for the 2025/26 return is 31 January 2027. The paper deadline is 31 October 2026. GOV.UK

Do I need Self Assessment if I am self-employed?

If you were a sole trader and had gross trading income of more than £1,000 during the tax year, HMRC says you must send a tax return. GOV.UK

Do I need to register again if I already have a UTR?

Not necessarily. If you were previously registered but did not file last year, you may need to reactivate your account instead. GOV.UK

What happens if I register after 5 October?

Register as soon as possible. HMRC can issue a different filing deadline, but the tax-payment deadline remains 31 January 2027 and penalties can arise in relevant circumstances. GOV.UK

Can I submit my return before January?

Yes. You can file once the relevant tax year has ended and you have the information needed. GOV.UK

Final thoughts

5 October 2026 is an important deadline if you are new to Self Assessment for the 2025/26 tax year.

Do not wait until January to find out whether you should have registered.

Check now if, during 2025/26, you:

• Became self-employed
• Started a side business
• Received property income
• Had significant untaxed income
• Received foreign income
• Made taxable capital gains
• Had another reason to submit a return

If you need Self Assessment, getting registered in October gives you time to organise the return properly rather than dealing with everything immediately before the January deadline.

At Merranti Accounting, we help individuals, sole traders and business owners determine whether they need Self Assessment, prepare their returns and understand the tax they need to pay.

Contact Merranti Accounting if you need help with your 2025/26 Self Assessment.

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Written by Jack Smith MAAT

Senior Client Manager, Merranti Accounting

Jack is an AAT-qualified accountant with more than 12 years of experience supporting individuals, sole traders and owner-managed businesses. His work includes accounts, tax planning, forecasting and practical advice, including helping clients understand and meet their Self Assessment obligations.

Read more about Jack Smith →