More than three million people still need to file their tax returns, with around a week to go before the deadline.
Some 8.6 million people have already filed their return for the 2024-25 tax year, HM Revenue and Customs (HMRC) said.
It is urging taxpayers and agents who are yet to file to act now or risk missing the January 31 deadline and face an automatic £100 penalty.
The revenue body said 3.3 million customers still need to file.
People can find help and support at gov.uk.
Myrtle Lloyd, HMRC’s chief customer officer, said: “Don’t leave it until deadline day. Filing now will give you peace of mind that your tax return is completed and if you have tax to pay, you have a week to arrange payment.
“If you’re worried about paying your tax bill, you may be able to set up a payment plan online – search ‘difficulties paying HMRC’ on gov.uk.”
This year’s deadline falls on a Saturday. HMRC’s phone lines are open Monday to Friday from 8am to 6pm.
Phone lines will close on Friday January 30 and reopen on Monday February 2 – after the deadline. HMRC said it will offer webchat support on Saturday January 31 through its online services helpdesk.
Earlier in January, HMRC apologised after its helplines were down for part of a day due to a short-lived technical issue.
HMRC will consider customers’ reasons for missing the deadline. Those with a reasonable excuse may avoid a penalty.
People should also watch out for scams, with criminals purporting to be from HMRC.
