HM Revenue & Customs (HMRC) is set to issue fewer penalties for late tax returns this year.
Around 850,000 people are set to receive letters detailing the £100 fines over the coming two weeks, 550,000 fewer than a year ago.
A new fine structure is in place this year, with those who fail to get their returns in within three months of the deadline eligible for a £10 daily fine and risking a maximum fine of £1,600.
"We want the returns, not the penalties. So anyone who still has not sent theirs should do so as soon as possible," said Stephen Banyard of HMRC.
"People who receive a penalty notice should act now to avoid further penalties. They should send in their return, appeal if they think they have a reasonable excuse, or contact us if they think they should not have been in self assessment."
The deadline for filing tax returns online was delayed this year due to a strike by public sector union, the PCS. Traditionally, the deadline is 31st but those who completed the form online on 1st or 2nd February will not be issued with fines.
Appeals against the fines need to be submitted by 31st March.