Taxpayers who fail to file a tax return online by 31 January risk not just a £100 fine from but will also pay interest on any late tax due.

Despite the risk of a fine, a survey has found that nearly half of self-employed individuals plan to complete their tax returns with just a month or less to spare. This equates to approximately 2.1 million people in the UK who are still to tackle the task.

A quarter of respondents said that they plan to start their submissions with less than three weeks to go until the deadline, while 15% admitted they would leave the task until a week or less before files are due.

Tax software firm GoSimpleTax carried out the survey. It also found around 87,000 people, or 2% of self-employed individuals, are expected to attempt to file their tax return only on the deadline day itself 31 January.

One in four self-employed people report spending an entire working day or longer on their submissions, leading to concerns about the time it takes to complete a self-assessment tax return.

Mike Parkes, technical director at GoSimpleTax, said: "Submitting your tax return as early as possible is not just about avoiding the stress of a last-minute task. It's about protecting yourself from potential financial shocks and serious penalties. Our research shows that many people spend well over a day completing their tax eturns, which means that leaving it too late can risk missing the 31st January deadline entirely.

"If that happens, will issue an immediate £100 fine. On top of that, every additional day for up to three months incurs an additional £10 fine, adding up to £900. After that, additional fines can push the total to £1,600 if you file a year late."

Chances are you may need to fill in a tax return if:

• You are self-employed as a sole trader and have earned more than £1,000

• You are a partner in a business partnership

• You earn over £100,000 even if you pay tax via PAYE

• If have sent you a notice to complete one unless you contact them and they agree to cancel the notice

• You have any untaxed income from

• Renting out a property

• Tips and/or commissions received cash in hand rather than via payroll

• Interest on your savings or investments

• Dividends

• Foreign income (including foreign pensions)

will consider the following excuses as reasonable cause for not filing your return on time:

• A partner or close relative died shortly before the tax return or payment deadline
• You had an unexpected stay in the hospital
• You had a serious or life-threatening illness
• Your computer or software failed while you were preparing your online return
• You had issues with HM Revenue and Customs online services
• A fire, flood or theft stopped you from filing your tax return on time
• There were unpredicted delays in the post
• You were delayed by disability or mental illness
• You were unaware of or misunderstood your legal obligation
• You relied on someone else to send your return, and they did not.