For those unfamiliar with Self-Assessment or uncertain about the need to file a return, this article provides guidance. Common reasons include self-employment, income over £100,000, and income from untaxed sources. Inform HMRC by October 5, 2023, for the 2022/23 tax year. The article recommends using HMRC's online tool for clarification and outlines various scenarios that necessitate submission. Seek professional advice if you're uncertain.