Martin Lewis urges Brits to ‘act now’ before January deadline or risk £100 fine | Personal Finance | Finance
Martin Lewis is reminding Brits of one key deadline (Image: ITV)
Martin Lewis has urged millions of Britons to “act now” ahead of the looming Self Assessment deadline, warning that even a short delay could result in an immediate £100 fine and mounting interest charges.
With just days to go until the January 31 deadline, the money expert said anyone who has been told by HMRC to file a tax return should not put it off. In a video shared on his official TikTok account, Mr Lewis stressed that time is running out and that leaving it until the last minute can be costly.
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The Self Assessment deadline is looming (Image: Getty)
HMRC figures show the scale of the issue. As of January 5, 2026, around 5.65 million people still needed to submit their Self Assessment tax return for the 2024 to 2025 tax year. The deadline for online submissions is 11:59pm on 31 January.
Search data suggests many people only start thinking about Self Assessment in the final weeks of January. Analysis by SEO firm Four Pillars SEO shows online searches surge as the deadline approaches, indicating a rush for last-minute help. Mr Lewis warned this approach often backfires.
In his message, he said: “Do you need to do a tax return? If you do, it’s urgent.”
He added: “If you miss the deadline there’s a hundred quid fine.” That penalty applies even if you owe no tax or are only a day late.
Mr Lewis also highlighted another often overlooked cost. Late payment of tax attracts interest, currently set at 7.75%. “More painfully, there’s also 7.75% interest on unpaid tax,” he said.
For those struggling to complete the return on time, he suggested making an estimated payment anyway to reduce the interest bill.
“If you can’t do the form in time, have a rough guess of what you owe and pay that,” he said.
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Mr Lewis reminded viewers that anyone HMRC has told to complete a return must do so, even if they believe they do not owe anything.
Groups commonly required to file include the self-employed earning more than £1,000 in the tax year from April 6, 2024, to April 5, 2025, as well as some people claiming Child Benefit who may be affected by the High Income Child Benefit Charge.
Missing the deadline can quickly become expensive. After the initial £100 fine, daily penalties of £10 can be added after three months, up to £900.
Further penalties of £300 or 5% of the tax owed can follow at six and 12 months. Separate late payment penalties of 5% can also apply at 30 days, six months and 12 months, on top of interest.
Mr Lewis warned that delaying only adds stress. HMRC phone lines become busier, accountants are stretched, and resolving problems becomes harder. “Doing it early will relieve some of that pain,” he said.
