HMRC has already received almost 950,000 online 2020/21 self assessment returns, the tax authority has confirmed.
Over 63,500 taxpayers completed their returns on 6 April, the first day of the new tax year.
HMRC says this is part of a growing trend in early filers. In the last five tax years, the number of taxpayers choosing to file on the first day of the new tax year has almost trebled from 22,885 in 2017 to 63,521 in 2021.
The numbers show that more taxpayers are realising they can file at a time that suits them and avoid any last-minute rush to meet the deadline on 31 January, the tax authority adds.
Myrtle Lloyd, HMRC's Director General for Customer Services, said: 'There are many advantages to completing your self assessment tax return sooner rather than later, not least that if you're due tax refund you'll get the money within a few days.
'Our new online guide helps answer many of the questions customers have about self assessment.'
HMRC has also issued a warning to taxpayers to be aware of copycat HMRC websites and phishing scams.
HMRC's self assessment guide can be accessed here.