New to Self Assessment? Find out who must register by 5 October 2026, which income may trigger a tax return, what happens after registration and the deadlines for filing and payment.
The deadline can apply to newly self-employed people, landlords, new business partners and people with other untaxed income. It may also apply if you registered previously but did not need to send a return for 2024–25 and now need to reactivate your account.
This guide explains who should check their position, how registration works and what to do if the deadline has been missed.
In this guide
• What the 5 October deadline means
• Who may need to register
• The £1,000 trading-income rule
• Registration, reactivation and filing
• Important Self Assessment deadlines
• What happens if you register late
• How Number One Accounting can help
What does the 5 October deadline mean?
The 5 October deadline is for telling HMRC that you need to complete a tax return for the previous tax year. For income received between 6 April 2025 and 5 April 2026, the notification deadline is 5 October 2026.
You normally need to register by this date if you have not submitted a Self Assessment tax return before. You may also need to reactivate your account if you were registered in the past but did not need to submit a return for 2024–25.
Registration is not the tax return
Registering tells HMRC that you need to use Self Assessment. You must still prepare and submit the tax return separately by the relevant filing deadline.
Who may need to register for Self Assessment?
You should check whether you need to register if any of the following applied during 2025–26.
You started working as a sole trader
You must normally send a tax return if your gross self-employment income was more than £1,000 before deducting expenses. This can include income from freelancing, contracting, delivery work, driving, online selling or another trade carried on personally.
You became a partner in a business partnership
A new business partner normally needs to register individually for Self Assessment. The partnership may also have separate registration and tax-return responsibilities.
You received income from property or land
Landlords and other property owners may need to report rental income that was not fully taxed. This can include income from residential property, commercial property, land, jointly owned property or overseas property.
The property allowance and other tax rules may affect whether a return is required, so the gross income, ownership share and expenses should be reviewed before deciding.
You received other untaxed income
You may need a tax return if you received untaxed income such as:
• Tips or commission
• Savings interest
• Dividends or investment income
• Foreign income
• Taxable UK income received while non-UK resident
• Other income that has not been taxed through PAYE
HMRC’s September 2026 registration announcement specifically encouraged people with more than £2,500 of untaxed income to check their Self Assessment position. However, the correct treatment depends on the type and amount of income, tax already deducted and the person’s wider circumstances.
You had Capital Gains Tax to pay
You may need to submit a tax return if you disposed of an asset that increased in value and Capital Gains Tax is due. Separate reporting deadlines can apply to disposals of UK residential property, so do not wait for the Self Assessment deadline before checking the position.
You need to pay the High Income Child Benefit Charge
You may need a tax return if you are liable for the High Income Child Benefit Charge and it is not being collected through PAYE. Some taxpayers may now be able to pay the charge through HMRC’s PAYE service instead, so check which route applies before registering.
HMRC has asked you to submit a return
If HMRC has issued a notice requiring a tax return, do not ignore it. You should submit the return unless HMRC formally agrees that it can be withdrawn. A return can still be required even if you believe no tax is due.
How does the £1,000 trading-income rule work?
The £1,000 test is based on gross trading income before expenses, not profit. If your total gross trading income was more than £1,000, you will normally need to register and report it.
Example
A person earned £1,600 from weekend delivery work and spent £450 on allowable business costs. Their profit before considering any allowance is £1,150, but the registration test starts with the £1,600 gross income. As this is more than £1,000, they should check whether they need to register.
Someone earning £1,000 or less may still choose to complete a return, for example to pay voluntary Class 2 National Insurance contributions where eligible or to support a claim for certain benefits. Individual advice may be needed before making that decision.
Do existing Self Assessment taxpayers need to register again?
If you already submit a tax return every year and your Self Assessment record remains active, you would not normally register again. Use your existing Unique Taxpayer Reference and online account.
If you registered previously but did not have to send a return for 2024–25, you may need to reactivate your account for 2025–26. Reactivation is different from creating a second Self Assessment record, and you should not apply for another UTR unnecessarily.
How do you register for Self Assessment?
Individuals can check and register through the official GOV.UK Self Assessment registration service. HMRC’s improved online service allows eligible individuals to register through their Personal Tax Account using Government Gateway or GOV.UK One Login details.
Information commonly required includes:
• Full name, address and date of birth
• National Insurance number
• Existing UTR, if previously registered
• The date self-employment or another taxable activity began
• Business or partnership details, where relevant
• The reason a tax return is required
HMRC states that people using the improved individual service can receive their UTR in their online account within 72 hours. Agents continue to use the appropriate agent registration processes, including forms such as CWF1 or SA1 where relevant.
Key Self Assessment deadlines for 2025–26
| Deadline | What is due? |
|---|---|
| 5 October 2026 | Tell HMRC if you need to complete a return and are new to Self Assessment, or reactivate where required |
| 31 October 2026 | Paper tax-return filing deadline |
| 30 December 2026 | Online filing deadline if you want HMRC to consider collecting eligible tax through your PAYE code |
| 31 January 2027 | Online tax-return filing deadline and deadline to pay tax due |
Payments on account may also be due on 31 January and 31 July, depending on the taxpayer’s circumstances.
What happens if you miss the 5 October deadline?
Register as soon as possible. Missing 5 October does not mean that you should wait until the next tax year, and it does not automatically create an immediate fixed £100 penalty.
If you register after 5 October 2026, HMRC may give you a separate filing deadline of three months from the date of its letter or email. However, tax for 2025–26 must still normally be paid by 31 January 2027.
A failure-to-notify penalty may apply if HMRC was not told on time and tax remains unpaid after the normal payment deadline. The penalty is linked to the tax unpaid and the circumstances of the failure. Registering promptly, submitting the return and paying the tax by 31 January can therefore materially affect the outcome.
Separate penalties apply if a required tax return is filed late or tax is paid late. Interest may also be charged. Read the official GOV.UK Self Assessment penalty guidance.
What if you no longer need to send a tax return?
Tell HMRC as soon as possible if you believe a tax return is no longer required. Until HMRC confirms that the return has been withdrawn or your Self Assessment record has been updated, continue to meet any filing obligations shown on your account. Simply deciding not to file can lead to an avoidable late-filing penalty.
What records should you start gathering?
Registration is only the first step. To prepare an accurate return, start collecting:
• Sales, invoices and other business-income records
• Receipts and evidence of allowable expenses
• Bank and credit-card statements
• Property rental statements and expense records
• Employment P60 and P45 forms
• Pension, savings, dividend and investment information
• Details of capital disposals or foreign income, where relevant
Preparing early gives you more time to resolve missing information, understand the tax due and plan payment before 31 January.
How Number One Accounting can help
Number One Accounting can help individuals and small-business owners with:
• Checking whether a tax return is required
• Self Assessment registration or reactivation
• Recovering or confirming an existing UTR
• Organising income and expense records
• Preparing the tax calculation and tax return
• Submitting the return to HMRC
• Dealing with late returns and HMRC correspondence
Frequently asked questions
Is 5 October the deadline for submitting the tax return?
No. It is the normal deadline for telling HMRC that you need to complete a return. The online tax-return deadline for 2025–26 is 31 January 2027.
Do I register again if I already have a UTR?
Usually not. If your Self Assessment account is active, use your existing UTR. If it became inactive because no return was required last year, you may need to reactivate it instead.
I started self-employment but earned less than £1,000. Must I register?
Not usually solely because of that trading income, provided the gross amount was £1,000 or less and no exception applies. You may still need a return for another reason or may choose to file for specific purposes.
Does an employee ever need a Self Assessment return?
Yes. Employment does not prevent someone from needing a return. A return may be required because of self-employment, rental income, investment income, foreign income, capital gains or another reason.
Will I automatically receive a £100 penalty if I register after 5 October?
No. The immediate £100 penalty relates to filing a required tax return late. Late registration can lead to a failure-to-notify penalty, but whether one arises depends on factors including the tax unpaid at the payment deadline and the circumstances of the failure.
Can an accountant register and file for me?
Yes. An authorised tax agent can assist with registration, prepare the return and deal with HMRC. You remain responsible for providing complete and accurate information.
Not sure whether you need to register?
Number One Accounting can review your income, confirm the appropriate next step and help you meet your Self Assessment obligations.
Telephone: 020 3026 5008
WhatsApp: +44 7383 685130
This article provides general information only and does not constitute personal tax, accounting or legal advice. Individual circumstances and HMRC requirements may vary. Information reviewed on 30 September 2026.