A Self Assessment Tax Return is a system used by HM Revenue and Customs (HMRC) to collect Income Tax from individuals and businesses whose income isn't taxed at source. You need to file one if you are: Self-employed or a sole trader A company director Receiving rental income from property Earning income from overseas sources A high-income earner over £100,000 per annum Receiving income from savings, investments, or dividends exceeding certain thresholds Making capital gains over the tax-free allowance A partner in a business partnership