Thousands of taxpayers risk falling foul of HMRC’s rules this autumn, with two crucial deadlines approaching in October.
Missing either of them could leave households facing an instant £100 fine, with penalties spiralling to as much as £1,600 for serious delays.
Andrea L Richards, accountant and chief executive of Accounts Navigator, has urged individuals to act swiftly to avoid unnecessary charges, highlighting the 5 October self-assessment registration deadline and the 31 October paper return deadline.
Who needs to file?
A tax return is required in a range of circumstances. This includes the self-employed who earned more than £1,000 in the past tax year, members of business partnerships, individuals liable for Capital Gains Tax, or those paying the High Income Child Benefit Charge outside PAYE.
Others who may be caught by the rules include those receiving untaxed income such as rental earnings, tips, savings interest or income from overseas.
5 October deadline: Registering for self-assessment
Anyone submitting a self-assessment for the first time must notify HMRC by 5 October 2025. Failing to do so can extend the filing timetable, but Richards warns that delaying registration increases the risk of penalties if the final return is not submitted on time.
31 October deadline: Paper tax returns
Taxpayers choosing to file a paper return must ensure it reaches HMRC by 31 October 2025. Missing this deadline triggers an automatic £100 penalty, even if no tax is owed. Additional fines and interest may follow if the delay continues.
Online filing after October
Many believe that switching to online filing by the 31 January 2026 deadline will protect them from penalties if they miss the October cut-off. However, HMRC calculates late filing penalties from the point the first return was due, meaning the £100 charge will already have been applied. Filing online after October can help in some situations, but Richards stresses it is safer to meet the initial paper deadline where possible.
How penalties escalate
Penalties increase rapidly the longer a return is delayed. After three months, HMRC can impose daily charges of £10, capped at £900. Returns more than six months late attract an additional £300 fine or 5% of tax owed, whichever is greater. At 12 months, a further £300 or 5% is added, taking potential penalties to £1,600 — on top of any outstanding tax liability.
Consequences of not filing
Failure to file a return altogether leaves taxpayers exposed to harsher action. HMRC can issue an estimated tax bill, demand immediate payment with interest, and in extreme cases begin court proceedings.
Appeals against penalties
While HMRC does allow appeals against late filing penalties, taxpayers must first complete and submit the outstanding return. Only those with a “reasonable excuse” covering the entire late period will be considered for relief.
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Double HMRC deadlines this October could hit taxpayers with £100 instant fines