Self assessment taxpayers must file and pay their self assessment tax return before the 31 January 2025 deadline.
The tax authority says more than 12 million people need to file a tax return for the 2023/24 tax year and pay any tax owed by the deadline.
Over 3.5 million taxpayers have already beaten the clock and submitted their returns, it adds.
HMRC is reminding others that starting their self assessment early means they are more likely to complete an accurate tax return, avoid any last-minute panic plus they will know what they owe sooner and can budget.
Myrtle Lloyd, HMRC’s Director General for Customer Services, said:
‘The countdown to the self assessment deadline has begun but there is still time to thoroughly prepare and file an accurate tax return by 31 January. You can access online help and support to help you file.’