This guide gives easy-to-understand advice for individuals in the United Kingdom who are confused about whether they need to complete a Self-Assessment tax return. It details the circumstances that necessitate a tax return, for instance being self-employed, a partner in a business, or having untaxed income. The article also demystifies the higher rates of income tax, detailing the thresholds at which the 40% and 45% rates apply. Additionally, it highlights the critical £100,000 income level where the personal allowance starts to be withdrawn, creating an effective 60% tax rate for some earners, and proposes ways to lessening this.