Anyone required to complete a self-assessment tax return for the 2017/18 tax year has only 99 days left to file it before the midnight deadline on 31 January 2019.
Individuals or businesses whose income is not automatically taxed, and those who have earned additional untaxed income, will usually have to complete a tax return every year.
Government statistics show that more than 11 million people completed self-assessment last year, of which 10.7 million filed their return on time.
With 45% of returns submitted in January 2018, and 758,707 left to the final day, HMRC is urging those filing this year to complete their tax returns earlier and avoid the last-minute stress.
Angela MacDonald, director-general for customer services at HMRC, said:
"Time flies once the festive period is under way, yet the niggle to file your tax return remains.
"We want to help people get their tax returns right.
"Starting the process early and giving yourself time to gather all the information you need will help avoid the last minute, stressful rush to complete it on time."
Talk to us about filing self-assessment.