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Getting Your Head Around Tax Self Assessment UK

Navigating the tax self-assessment process in the UK can initially seem daunting, especially for those new to the system. However, understanding the steps and requirements can make the process more manageable and ensure compliance with HM Revenue and Customs (HMRC) regulations. Here’s a comprehensive guide to getting your head around tax self-assessment in the UK.

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What is Tax Self-Assessment?

Tax self-assessment is a system used by HMRC to collect Income Tax. Unlike the PAYE system, where tax is deducted at source by employers, self-assessment requires individuals to calculate and report their own tax liability. This process is typically required for self-employed individuals, those with additional income, landlords, company directors, and others with complex tax situations. The system is complicated, so many people seek help from Chartered Accountants to ensure they get it right.

Who Needs to File a Self-Assessment Tax Return?

You have to file a self-assessment tax return if:

  • You are self-employed, or a partner in a business.
  • You have rental income or other untaxed income.
  • You are a company director.
  • You have received income from investments or savings.
  • You have earned more than £100,000.
  • You need to claim certain tax reliefs or allowances.

Registering for Self-Assessment

To begin, you must register for self-assessment with HMRC. If you’re self-employed, you should register as soon as you start your business. For others, registration is required by 5 October following the end of the tax year for which you need to file. Registration can be done online on the HMRC website. Once registered, you’ll receive a Unique Taxpayer Reference (UTR) number and be able to set up your online account.

Key Deadlines

Understanding the deadlines is fundamental to avoid penalties:

  • Register for self-assessment: By October 5th following the end of the tax year.
  • Paper tax return: By October 31st following the end of the tax year.
  • Online tax return: By January 31st following the end of the tax year.
  • Pay the tax you owe: By 31 January following the end of the tax year (and a second payment by 31 July if you make advance payments).

Completing Your Tax Return

1. Gather Your Information: Collect all relevant financial records, including income from employment, self-employment, rental properties, dividends, savings, and any other sources. Also, gather records of allowable expenses and reliefs you can claim.

2. Log in to Your Online Account: Use your UTR and password to log into the HMRC online service. Ensure your contact details are up-to-date.

3. Fill in the Tax Return: Complete the sections relevant to your income and expenses. HMRC’s online system will guide you through the process, providing prompts and explanations.

4. Calculate Your Tax: The online system will calculate your tax liability based on the information provided. It’s advisable to double-check these calculations or consult with a tax advisor if your situation is complex.

5. Submit and Pay: Submit your completed tax return online. Ensure you pay any tax due by 31 January to avoid interest and penalties.

Common Allowable Expenses

For self-employed individuals, understanding allowable expenses can reduce your tax bill. Common expenses include:

  • Office costs (e.g., stationery, phone bills).
  • Travel expenses (e.g., fuel, parking, train fares).
  • Clothing expenses (uniforms or protective clothing).
  • Staff costs (e.g., salaries, subcontractor costs).
  • Financial costs (e.g., insurance, bank charges).
  • Costs of goods bought for resale.
  • Advertising or marketing costs.

Keeping Records

Keeping accurate records is essential for a smooth self-assessment process. HMRC requires records to be kept for at least five years after the January 31st submission deadline of the relevant tax year. This includes:

  • Bank statements and receipts.
  • Sales and purchase invoices.
  • Payroll records (if applicable).
  • Any other documentation that supports your income and expenses.

Dealing with Penalties

Failing to meet deadlines or providing incorrect information can result in penalties. These can range from late filing penalties to inaccuracies in your return. It’s essential to file on time and ensure your return is accurate. After submission, you can amend your return if you realise you’ve made a mistake.


Getting your head around tax self-assessment in the UK involves understanding who needs to file, meeting key deadlines, accurately completing the tax return, and keeping meticulous records. By following these steps and possibly seeking professional advice, you can confidently navigate the self-assessment process and ensure compliance with HMRC regulations.