The £100 penalty for missing the 31st January midnight self-assessment deadline is negligible. That is, compared to what HMRC will charge you in interest.
The more pressing financial danger facing millions of self-employed workers is HMRC’s 7.75% interest rate on unpaid tax – a charge that kicks in from 1st February and can rapidly cost you hundreds of pounds more than the initial fine.
With just days remaining until the Self Assessment deadline, tax compliance experts are warning that late payment interest, not the headline penalty, poses the greatest threat to freelancers’ finances.
The £100 penalty is just the start
More than 11.5 million people need to file their Self-Assessment tax return for the 2024/25 tax year, and based on previous years’ patterns, approximately 1.1 million are expected to miss the deadline. The immediate consequence is a £100 penalty, regardless of whether any tax is actually owed.
But according to Qdos, a UK contractor tax insurance and compliance firm, this initial fine pales in comparison to the escalating interest charges that follow.
HMRC interest rates
From 9 January 2026, HMRC’s late payment interest rate stands at 7.75%, applied to anyone who has filed their return but failed to pay what they owe by the deadline. This rate kicks in from 1st February 2026 and continues accruing until the bill is settled in full.
Seb Maley, CEO of Qdos, issued a warning to self-employed workers: “Being hit with a £100 penalty isn’t ideal at the best of times, but the interest charged by HMRC to those who don’t pay their tax on time is the real kicker – and can cost a lot more than £100 if you’re not careful.”
He continued: “Currently set at 7.75% of the amount owed from the 1st February, this can mount up quickly – to the point where, before you know it, not paying on time has cost you hundreds. This is the case even if you’ve set up a Time to Pay arrangement with HMRC, which allows you to spread the cost of your tax bill over several months.”
Unfair repayment rate gap
Adding insult to injury, HMRC pays just 2.75% interest on money it owes to taxpayers who have overpaid their tax – less than half the rate it charges for late payments.
“And if you’ve paid too much tax and you’re due a refund?” Maley asked. “HMRC will only pay 2.75% interest on money it owes to you – less than half of what it charges to those who are late paying their tax bill.”
This disparity reflects HMRC’s policy of setting late payment interest at the Bank of England base rate plus 4%, while repayment interest is calculated at the base rate minus 1%, subject to a minimum floor of 0.5%.
Beyond penalties: Compliance check risk
Perhaps most concerning for freelancers and contractors is the increased scrutiny that comes with late filing or payment. As Maley pointed out: “There’s also the reality that filing or paying late puts you firmly on HMRC’s radar. So, penalties and interests aside, you run the risk of HMRC carrying out a compliance check – something that can cost tens of thousands of pounds to shut down.”
Last year, more than 732,000 people filed their returns on deadline day itself, with the peak filing hour occurring between 4pm and 5pm when over 58,000 returns were submitted. Another 31,000-plus left it until the final hour before midnight.
How penalties can quickly escalate
For those who miss the 31st January deadline, the penalties quickly multiply:
- Day 1 after deadline: Automatic £100 fine
- Three months late: Daily penalties of £10 per day, up to a maximum of 90 days (£900 total)
- Six months late: The higher of £300 or 5% of the total tax due
- Twelve months late: Additional penalties based on a percentage of unpaid tax
Meanwhile, interest continues accruing on any outstanding balance from 1st February at the 7.75% rate, compounding the financial impact.
Time to pay arrangements still incur interest
Even taxpayers who arrange a payment plan with HMRC aren’t exempt from interest charges. Time to Pay arrangements allow you to spread tax payments over several months if you owe £30,000 or less and are within 60 days of the payment deadline, but the 7.75% interest rate continues to apply to the outstanding balance.
To qualify for a Time to Pay arrangement, you must:
- Be up to date on your Self Assessment filing
- Have a tax liability of £30,000 or less
- Be within 60 days of the payment deadline
- Have no other outstanding payment plans or debts with HMRC
What to do next year
More than 3.5 million people had already filed their returns by October 2025, giving themselves peace of mind and time to prepare for payment. Filing early offers several advantages:
- Know your bill in advance: Understanding what you owe allows for better financial planning
- Avoid technical issues: HMRC’s systems experience high traffic in late January, potentially causing submission problems
- Time to organise payment: If you can’t pay immediately, you have time to set up a payment plan before the deadline
- Reduce stress: Eliminate the last-minute panic that affects hundreds of thousands each year
Unable to pay?
For freelancers who find themselves unable to pay their full tax bill by the deadline, contacting HMRC to arrange a Time to Pay agreement before 31st January is essential. While interest will still apply, it prevents additional penalties and demonstrates good faith compliance – potentially keeping you off HMRC’s radar for more intensive scrutiny.
As Maley warns in the world of Self Assessment, the visible penalty is just the tip of the iceberg. The real cost lies beneath the surface, accruing silently at 7.75% until the debt is finally cleared.
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