Who actually has to file a self assessment tax return?
Anyone whose income is not fully taxed at source or whose circumstances fall into defined categories — and the obligation is yours to identify, which is the part that catches people out. Nobody necessarily tells you that you need to file.
The main triggers:
Self-employment above a small trading threshold.
A partner in a partnership.
Untaxed income — rental income, investment income above allowances, foreign income, tips and commission not taxed through payroll.
Capital gains above the annual exempt amount, or where disposal proceeds exceed a reporting threshold — and property disposals have their own separate, much shorter reporting deadline, which is a common and expensive miss.
High income child benefit charge, where income exceeds the threshold and you or a partner claim child benefit.
Higher rate taxpayers claiming pension relief on personal contributions, since the additional relief above basic rate is not given automatically.
Company directors in some circumstances.
Income above a defined level, which triggers the requirement regardless of source.
Claiming certain reliefs and expenses.
The deadlines:
Register by 5 October following the end of the tax year in which the liability arose.
Paper returns by 31 October, online by 31 January.
Payment by 31 January, plus a payment on account — an advance instalment toward the following year, which surprises first-time filers who expected one bill and receive one and a half.
A second payment on account by 31 July.
Penalties are automatic — a fixed penalty for missing the deadline even if no tax is due, then escalating daily and percentage-based penalties, plus interest.
What actually makes it manageable: keeping records as you go rather than reconstructing them; registering early, since the process takes time; and using the digital account to check what has been reported.
Making Tax Digital is progressively changing this for the self-employed and landlords, introducing quarterly reporting.
General information, not tax advice.