From self-employment to rental income, there are many reasons you may need to file a Self-Assessment return. Know the triggers and register with HMRC by 5 October if this is your first time.

There are a number of reasons why you might need to complete a self-assessment return. This includes if you are self-employed, a company director, have an annual income over £150,000 and / or have income from savings, investment or property.

You must file a self-assessment tax return if any of the following apply to you during the tax year:

• You were self-employed as a sole trader and earned more than £1,000 (before expenses).
• You were a partner in a business partnership.
• Your total taxable income exceeded £150,000 in the 2025–26 tax year. However, even if your income is under £150,000, other factors (such as rental income or capital gains) may still require you to file a self-assessment return.
• You had to pay Capital Gains Tax on the sale or disposal of assets.
• You were liable for the High Income Child Benefit Charge.
• You had other sources of untaxed income, such as:
  • Rental income from property
  • Tips or commission
  • Savings and investment income (including dividends)
  • Foreign income

If you need to file a self-assessment return for the first time, you must inform HMRC by 5 October following the end of the tax year. For the 2025–26 tax year (which ends on 5 April 2026), the deadline to register is 5 October 2026.

HMRC has an online tool www.gov.uk/check-if-you-need-tax-return/ that can help you check if you are required to submit a self-assessment return.