HM Revenue & Customs said around 12 million people are expected to submit a Self Assessment tax return for the 2025 to 2026 tax year, with the online deadline set for 31 January 2027. In a release published on 23 October 2026, the department said 100 days remained at that point and urged customers to file ahead of the January rush.

The department said filing early lets customers learn how much tax they owe before the deadline, budget with more time, receive a refund sooner if they have overpaid, and avoid penalties. Returns can be completed on GOV.UK, and a GOV.UK tool is available for anyone unsure whether they need to file. People new to Self Assessment must first register to receive a Unique Taxpayer Reference. Those with PAYE income can file online before 30 December and have tax owed collected through their tax code, HMRC said.

Separate arrangements include a paper return deadline of 31 October 2026. HMRC also warned that criminals often impersonate the department to steal money or personal information, and advised people to check whether unexpected requests are genuine before sharing details.