HM Revenue and Customs (HMRC) customers have been put on high alert and warned against incurring a steep £100 penalty. Time is quickly running out for millions of people to file their tax returns before the deadline on January 31.

According to the latest data, some 3.4 million individuals have still not filed in the necessary information. The deadline affects anyone self-employed or part of a business partnership with last year’s pre-tax earnings exceeding £1,000, specifically for the tax year spanning from April 6, 2023, to April 5, 2024.

There are also other scenarios where filing is necessary. These could include having an annual taxable income over £150,000, any need to pay Capital Gains Tax, or accountability for the High Income Child Benefit Charge.

Additionally, if you have specific types of untaxed revenue, like funds from foreign shores or unpaid gains from savings, dividends, investments, tips and commissions, or property lettings, you’ll be expected to complete a self-assessment. In a notice regarding the issue, Myrtle Lloyd, HMRCs Director General for Customer Services, said: “The countdown to the Self Assessment deadline has begun, but there is still time to thoroughly prepare and file an accurate tax return by 31 January.”

For those who must tackle the filing process, Lloyd stresses the use of available online help, stating: “You can access online help and support to help you file. Search ‘help with Self Assessment’ on GOV.UK to find out more.”

Be mindful of the £100 fines that will be imposed for any late submissions. An estimated 12 million individuals are expected to submit their tax returns for the 2023 to 2024 tax year and pay any outstanding taxes by the deadline of 31 January 2025.

For those unfamiliar with the Self Assessment process, it’s recommended to register well ahead of time to obtain your Unique Taxpayer Reference, which will allow you to file for the 2023 to 2024 tax year. You can register for a self-assessment on GOV.UK here.

Once officially registered, you can use your online account to submit a Self Assessment return. Simply log into GOV.UK with your Unique Taxpayer Reference (UTR) number and follow the instructions provided on-screen.

Detailed information about who needs to file a self-assessment and who doesn’t can be found here.