HM Revenue and Customs (HMRC) has issued a stark warning to millions of workers across the United Kingdom: submit your online Self Assessment tax return by the critical deadline or face substantial financial penalties.
The Critical January Deadline
The vast majority of individuals required to complete a Self Assessment must settle their tax bill and file their return online by 11.59pm on 31 January 2026. This deadline is specifically for the 2024/25 tax year. Those who are new to the system must ensure they have their Unique Taxpayer Reference (UTR) ready to file correctly.
It is crucial to note that this January cut-off applies only to online submissions. The deadline for paper tax returns passed much earlier, on 31 October 2025. Anyone who missed that paper deadline is already subject to a late filing penalty.
How Penalties Escalate Rapidly
HMRC wields significant power to impose financial penalties for late tax returns, and the costs can accumulate alarmingly fast. The process begins with an immediate fixed £100 penalty for missing the 31 January deadline.
The situation deteriorates if the return remains unfiled:
- After three months, daily penalties of £10 per day can be charged, up to a maximum of £900.
- Once six months have passed, a further penalty of 5% of the tax owed or £300 is applied, whichever is greater.
- After 12 months, another 5% or £300 charge (whichever is higher) is added.
Separately, late payment penalties also apply. Taxpayers who do not pay what they owe will incur a 5% charge on the unpaid tax after 30 days, with additional 5% penalties at the six-month and 12-month marks. Interest is also charged on any outstanding tax from the date it was due.
What To Do If You Receive a Penalty
If HMRC issues a penalty for a late return or late payment, you may have grounds to appeal. According to official guidance, you can dispute the penalty if you have a 'reasonable excuse' for missing the deadline.
Typically, you have 30 days from the date the penalty is issued to contact HMRC and formally lodge an appeal. You will need to provide a clear reason for the delay. The process for making an appeal varies depending on your employment status and the type of tax involved.
HMRC stresses that these costly penalties are entirely avoidable by simply submitting your Self Assessment tax return promptly before the January deadline expires.
