There are several reasons why you might need to file a self-assessment tax return. This could apply if you are self-employed, a company director, have an annual income over £150,000, or receive income from savings, investments 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 below £150,000, other factors (such as rental income or capital gains) may still mean you need 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:
    o Rental income from property
    o Tips or commission
    o Savings and investment income (including dividends)
    o Foreign income

If you are filing a self-assessment return for the first time, you must notify HMRC by 5 October following the end of the tax year. For the 2025–26 tax year (ending 5 April 2026), this means the registration deadline is 5 October 2026.

HMRC provides a helpful online tool to check whether you need to submit a self-assessment return: 

Source:HM Revenue & Customs | 15-02-2026
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Aitch
I'm Aitch, the Founder and CEO of CIGMA Accounting Ltd. As a Chartered Management Accountant and as a CIMA member, I've spent more than 16 years helping businesses, entrepreneurs, landlords, and individuals with tax planning, accounting, and HMRC compliance. As a chartered accountant in London, I'm passionate about making complex tax matters easier to understand and helping clients make confident financial decisions. Over the years, I've advised start-ups, SMEs, established companies, and high-net-worth individuals across a wide range of tax and accounting matters. My expertise includes Corporation Tax, Self-Assessment, Capital Gains Tax, Inheritance Tax planning, R&D tax relief, capital allowances, international tax, and resolving complex HMRC compliance issues. Whether clients need a business accountant, tax accountant, or strategic tax advisor, my focus is always on delivering practical advice that creates long-term value. One of my specialist areas is Making Tax Digital (MTD). I've worked extensively with businesses preparing HMRC's digital reporting requirements, helping them move to cloud accounting, improve financial processes, and adopt technology that makes compliance more efficient. I regularly speak at Making Tax Digital roadshows, industry events, and educational sessions in collaboration with Zoho Books, sharing practical insights into digital accounting, tax legislation, and the future of the profession. Many business owners looking for the best accounting firm in London are not simply searching for an accountant they're looking for trusted advice, responsive support, and long-term value. That's the approach I've taken in building CIGMA Accounting. My team and I work closely with businesses across London and the UK, providing accounting services, tax advisory, bookkeeping, payroll, VAT, company accounts, and strategic tax planning tailored to each client's goals. Through this website, I share practical guidance on UK taxation, Making Tax Digital, HMRC updates, Corporation Tax, Self-Assessment, and business finance. My aim is to provide reliable, straightforward information that helps business owners understand changing regulations, reduce compliance risks, and make informed financial decisions with confidence.
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