Over one million taxpayers filed their 2023–24 returns late this year. While HMRC announced an extension for some traders grappling with the transitional rules for basis period reform, many will receive an automatic penalty.

The penalties for late filing of self assessment tax returns are designed to encourage timely compliance with tax obligations and vary depending on the length of the delay in filing the return. In summary, if a self-assessment tax return is filed late, an initial fixed penalty of £100 is imposed, regardless of whether any tax is due or has been paid on time. This penalty applies immediately after the filing deadline has passed.

Note that there was an extension where those affected by basis period reform had sought an overlap relief figure prior to 31 January, but a response had not been received until later.