HM Revenue and Customs (HMRC) will begin sending tax letters to UK households from Tuesday, October 6, targeting those who have missed a key registration deadline. Under HMRC rules, anyone who needs to complete a tax return but has not yet registered for Self Assessment must do so by today, October 5.
Once registered, taxpayers have until 11.59pm on January 31, 2027, to submit their tax return and pay any tax owed for the previous tax year. However, missing the October 5 deadline means HMRC will start sending letters after this date with a new deadline for sending the tax return, and a "failure to notify" penalty may also be handed out.
Penalties and payment deadlines
Missing the October 5 deadline not only risks a fine, but it also does not provide extra time to pay the tax bill. Taxpayers must still pay the tax they owe by 11.59pm on January 31, 2027.
HMRC said: "You must tell HMRC by 5 October if you need to complete a tax return for the previous year and you have either: not sent a tax return before; registered before but did not need to send a tax return for the tax year 2024 to 2025."
HMRC added: "You could be fined if you do not tell HMRC by 5 October."
Who must send a tax return
A tax return must be sent to HMRC if, in the last tax year from April 6 to April 5, any of the following applied: being self-employed as a 'sole trader' and earning more than £1,000 (before taking off anything claimable as tax relief); being a partner in a business partnership; having to pay Capital Gains Tax when selling or "disposing of" something that increased in value; having to pay the High Income Child Benefit Charge and not paying it through PAYE; or being an off-payroll worker who is repaying a student or postgraduate loan.
A tax return may also be needed if there is any untaxed income, such as money from renting out property, tips and commission, savings interest, dividends or foreign income.
Late registration and penalties
If registering for Self Assessment after October 5, a letter or email from HMRC will arrive with a different deadline to send the tax return by, which will be three months from the date on the letter. The tax owed must still be paid by January 31, 2027.
HMRC said: "If you register after 5 October and do not pay all of your tax bill by 31 January, you may get a 'failure to notify' penalty. This penalty is based on the amount still left to pay and you'll receive it within 12 months after HMRC receives your Self Assessment tax return."
The letter from HMRC will state the penalty amount and how it has been calculated. If there is anything not agreed with, or information that has not been considered, HMRC must be told "straight away".
HMRC added: "After taking account of anything you've told us, we'll then either: send you a penalty assessment notice; invite you to enter into a contract with us to pay the penalty, together with the tax and interest. In certain circumstances you may also have to pay interest on the penalty if you don't pay it on time."
