The tax authority said more than 10.2 million returns were filed ahead of the original deadline, leaving 2.3m still to file.
Late-filers had until 28 February 2022 to file their 2020/21 tax returns online before being fined, due to pressures ensuing from the pandemic.
However, interest on outstanding tax bills is accruing at 3% and HMRC’s late-filing penalties regime kicks in as usual from 1 March 2022.
Late-paying taxpayers have until 1 April 2022 to pay their tax bills in full, or set up a time-to-pay arrangement.
These arrangements spread the cost of repaying tax bills of up to £30,000 into manageable monthly instalments, usually over a period of up to 12 months.
A 5% late-payment penalty will be charged if tax is not paid or a payment plan has not been set up by midnight on 1 April 2022.
Myrtle Lloyd, director-general for customer services at HMRC, said: “I’d like to thank the millions of customers and agents who sent us their tax returns and paid in time for January’s deadline.
“Customers can set up a monthly payment plan online if they’re worried about paying their tax bill.”