An estimated one million customers failed to file their Self Assessment returns by the 31 January deadline, according to figures from HM Revenue and Customs.
HMRC said 11,489,825 returns were received by the cut-off for the 2024–25 tax year, out of 12,029,168 expected. Of those submitted, more than 97 per cent were filed online, highlighting the continued shift to digital.
Pressure peaked on deadline day, with 475,722 taxpayers filing on 31 January alone. The busiest hour was 5pm–6pm, when 32,982 returns were submitted, while 27,456 people filed in the final hour before midnight. To cope with demand, HMRC unusually opened helplines on Saturday, handling 10,483 calls and 5,409 webchats.
HMRC is urging anyone who missed the deadline to act quickly to avoid escalating penalties and interest. Late filers face an immediate £100 fixed fine, followed by £10 daily penalties after three months (up to £900), then additional charges at six and 12 months. Separate penalties also apply for late payment, alongside interest.
Myrtle Lloyd, chief customer officer at HMRC, said: “Thank you to the millions of people and agents who filed their Self Assessment tax return and paid any tax owed by 31 January. Anyone who missed the deadline should file their return as soon as possible, as penalties and late payment interest may be charged. HMRC digital channels are always the quickest and easiest way for people to sort their tax affairs.”
Returns can still be submitted and tax paid via GOV.UK, with the HMRC app among the fastest payment options. Time to Pay arrangements are also available for eligible customers who cannot settle their bill in full.
HMRC has also reminded that Making Tax Digital for Income Tax will become mandatory from 6 April 2026 for sole traders and landlords with qualifying income over £50,000, requiring quarterly updates of income and expenses. The tax authority is encouraging affected businesses to sign up early to prepare for the change.
Meanwhile, Self Assessment customers will be able to file returns for the 2025–26 tax year from 6 April 2026.