HM Revenue and Customs (HMRC) is urging high-income Child Benefit parents who have not yet submitted their tax return to take action now, or face penalties.
Parents with incomes above £50,000 who continued to receive Child Benefit after January 7, 2013 have to pay a tax charge.
This is based on their incomes and how much Child Benefit they received in the 2012-13 tax year.
Those who have already registered must now file a return before January 31.
Those who have neither registered nor opted out must register for Self Assessment Online now, to enable them to send an online return by the January 31 deadline.
This is because online registration can take up to seven working days to complete, as HMRC has to send an Activation Code in the post. The deadline for paying any tax owed for 2012-13 also falls on January 31.