LONDON, Oct 1 – HM Revenue and Customs (HMRC) has issued an urgent warning that taxpayers could face fines of up to £1,600 if they miss two critical Self Assessment deadlines in October.
Taxpayers required to file must register with HMRC by October 5, 2025, while paper returns for the 2024/25 tax year must arrive by October 31, 2025.
Registration deadline approaches
Andrea L Richards, chief executive of Accounts Navigator, stressed that anyone new to the system must act quickly.
“Anyone needing to submit a tax return for the first time must notify HMRC by October 5, 2025,” she said. “Delaying registration raises the risk of missing deadlines and incurring penalties.”
The requirement applies to self-employed workers earning more than £1,000, business partners, landlords with rental income, and those liable for capital gains tax.
Paper return cut-off
The second key date is October 31, 2025, for paper returns covering the 2024/25 financial year.
Richards cautioned that missing this deadline can still result in fines, even if a taxpayer files online by the January 31, 2026 deadline. “HMRC calculates penalties from the date the first return is received,” she explained.
Growing penalty risks
Penalties escalate sharply for late submissions. Returns filed more than three months late face daily charges of £10, which can add up to £900.
After 12 months, HMRC imposes either a £300 penalty or 5 per cent of the unpaid tax, whichever is higher.
Maximum fines of £1,600
In severe cases, fines for late filing can total £1,600, in addition to the outstanding tax bill. HMRC can also estimate a taxpayer’s liability and demand immediate payment with interest.
“In total, penalties for serious delays can reach £1,600, in addition to any tax owed,” Richards warned.
New rules from 2026
From April 2026, Self Assessment will be replaced by Making Tax Digital for Income Tax, requiring five submissions a year instead of one.
George Holmes, managing director of Aurora Capital, explained: “Under the old rules, a late filing meant an immediate £100 fine. From April 2026, missed deadlines will operate under a points-based system, with a £200 fine after four penalty points.”
Expert warnings
Tax specialists say the changes could be challenging for individuals unfamiliar with digital tax reporting. Payment deadlines will also tighten, with penalties starting after just 15 days, rather than the current 30.
Holmes added: “This shift will demand more discipline from taxpayers. The risk of slipping into penalty territory will be far higher.”
HMRC enforcement powers
In extreme circumstances, HMRC can pursue non-compliant taxpayers in court. Officials stressed that meeting deadlines is the only way to avoid escalating fines and legal risks.
With £42.8 billion in unpaid tax currently outstanding, the government has stepped up enforcement with new staff and digital systems to increase compliance.
Summary
The looming October deadlines highlight the growing importance of tax compliance as HMRC adopts tougher penalties and prepares for digital reporting. With fines of up to £1,600 at stake, taxpayers are urged to act early to avoid costly mistakes.
Major reforms arriving in April 2026 will reshape the Self Assessment system, demanding more frequent filings and reducing grace periods for payment. Tax experts warn that individuals must prepare now to adapt to the new framework.
For ongoing updates on HMRC changes and practical tools to manage your tax obligations, download the Pie app, designed to help you stay one step ahead of shifting deadlines and regulations.
