Do you have extra income? Register for Self Assessment by 5 October

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Do you earn extra income as a freelancer, rent out a room, or sell online through platforms like Amazon or eBay? If your income from these sources exceeds £1,000 per year, you must register for Self Assessment, which is the UK system of self-assessment tax. This usually applies to people with income outside of PAYE (Pay As You Earn) who exceed certain income thresholds outside of their regular employment where tax is deducted automatically.

In this article, we explain who needs to register for Self Assessment, what it is and how to obtain a UTR number, how to set up a Government Gateway account, and what you need to prepare in order to submit your self-employment tax return in the UK on time. Remember: you must register by 5 October and submit your tax return and pay your tax by 31 January.

Who must register for Self Assessment and when?

Not every resident of the United Kingdom is required to complete a Self Assessment, but if you earn income outside of PAYE, this obligation may also apply to you. Registration for Self Assessment is necessary, among other things, if:

  • you have started a business as a sole trader (self-employed),
  • you rent out property,
  • you rent out a room and the income from such rental exceeds £7,500 (Rent-a-Room Scheme),
  • you sell goods online (e.g. via eBay, Amazon, etc.),
  • you are a company director with additional income,
  • you have income from abroad that must be reported in the UK.

If you have income from abroad, in most cases you must declare it in your Self Assessment tax return, even if it is taxed in the country where it was earned. The rules depend on the double taxation agreement between the country in question and the UK.

If you started an additional business during the tax year ending 5 April 2025, you have until 5 October 2025 to register. Your tax return and payment must be submitted by 31 January 2026.

What are the most common mistakes in this area? The most common mistakes are confusing Self Assessment with PAYE, forgetting about income from Poland, or delaying registration until January, which often results in late registration or payment penalties.

UTR number – what is it and how can you get one?

UTR number, or Unique Taxpayer Reference, is an individual taxpayer number assigned by HMRC. Without it, you cannot file a Self Assessment return or add this service to your online account. To obtain a UTR, register for Self Assessment on the GOV.UK website (form ‘Register for Self Assessment and get a tax return’). The form requires you to provide:

  • your National Insurance number,
  • your UK address,
  • the date you started your business or additional income source,
  • a description of your business (e.g. ‘freelance graphic design’).

After submitting your application, HMRC will send a letter with your UTR to your address, usually within 10 working days. Make sure your address details are up to date – an incorrect address may delay the entire process.

How do I set up a Government Gateway account and link it to HMRC?

To manage your online tax return, you need a Government Gateway account – this is the portal through which you log in to the HMRC system. The registration process is simple and consists of a few steps:

  • 1. Go to GOV.UK – GOV.UK – HMRC online services.
  • 2. Select ‘Create sign in details’ and enter your e-mail address.
  • 3. Set a password and save the User ID you receive.
  • 4. Ensure that you register your account as an individual, not as an organisation, if you are self-employed.
  • 5. Verify your identity – you may need your passport, ID card or credit card details.

Adding the Self Assessment service

  1. After logging into your account, select “Add a tax, duty or scheme” → “Self Assessment.” Enter your UTR number and then confirm the activation. A confirmation code may be sent by post within a few days – without it you won’t be able to submit your return.
  2. Tip: Save your login details in a secure place and avoid creating multiple Government Gateway accounts, as it will make communication with HMRC more difficult.

The final step: what do you need to prepare to file your tax return by 31 January?

Once you have your UTR number and an active Government Gateway account, you can prepare to file your tax return. This is the stage where you gather all the necessary documents. For this purpose, you will need:

  • a statement of income and expenses (e.g. invoices, bills),
  • documents from your employer – P60, P45 or P11D,
  • information about income from rentals or online sales,
  • data on income from Poland (if it relates to the UK tax year),
  • the bank account number from which you will pay the tax.

If you are self-employed, prepare a statement of income and expenses for the tax year (from 6 April to 5 April). It is also a good idea to keep copies of invoices, receipts and payment confirmations for 5 years from the date of filing your tax return – HMRC may request them during an audit.

What mistakes should you avoid? First and foremost – don’t wait until the last day! Late submission after 31 January results in an automatic penalty. Another common problem is not including income from Poland. If you prefer, you can have your tax return prepared by an accountant – this will save you time and stress.

Get your Self Assessment done by experienced specialists

If you earn additional income in the UK from freelancing, renting or online sales, remember that you are required to register for Self Assessment. Obtain your UTR number, set up a Government Gateway account and prepare all the necessary documents so that you can file your tax return by 31 January.

Do not risk penalties for late filing – register with the system by 5 October, and if you do not know where to start, contact Essence Accounting. Our team’s support will help you go through the entire process without stress and prepare your self-employment tax return in the UK by the deadline.

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