Self Assessment is how you report income that PAYE cannot handle: self-employment, rental income, significant dividends or savings interest, HICBC, and capital gains. The tax year runs to 5 April; the paper return deadline is 31 October and the online deadline is 31 January, which is also when any balance owed is due.
Missing the deadline costs £100 immediately, with escalating penalties and late payment interest after that. If your bill is over £1,000 you will usually also make payments on account towards the following year. Estimate what you owe with the Self Assessment Tax Calculator and track every date on the tax deadlines calendar.
You start freelancing in May 2026. That income falls in the 2026/27 tax year, so you must register for Self Assessment by 5 October 2027 and file and pay by 31 January 2028. People are often surprised by the gap: nearly two years can pass between first invoice and first tax bill. The standard advice, setting aside 25% to 30% as you earn, exists to absorb that shock.
