What Happens If You Miss the Self-Assessment Deadline?
The Self-Assessment deadline is creeping closer, and every year thousands of people across the UK get caught out by leaving it too late.
Even if you owe no tax, missing the filing deadline can still land you with penalties that stack up quickly. HMRC’s system is strict, and once the fines start, they keep adding up until your return is filed.
Here’s exactly what happens if you miss the deadline and why it’s so important to file on time.
The Self-Assessment Deadline
The official deadline to submit your online tax return for the 2024 to 2025 tax year is 31 January 2026.
That date might sound far away, but it comes around faster than you think. Leaving it to the last minute often leads to errors, delays, or technical issues on the HMRC portal. File early, and you’ll avoid all of that stress (and the fines that follow).
The Penalties for Late Filing
If you miss the deadline, HMRC will issue fines that increase the longer your return is outstanding. Here’s what you can expect:
✅ £100 fixed penalty – This applies the day after the deadline, even if you owe nothing.
✅ £10 per day – After three months, daily penalties begin and can run for up to 90 days, adding another £900 in total.
✅ 5% of unpaid tax – At 30 days, 6 months, and 12 months after the deadline, HMRC can charge further penalties based on the amount of tax owed.
✅ Total fines can exceed £1,600 – And that’s before interest on late payments is added.
Even if your return is just one day late, you’ll still get the £100 fine. There are very few excuses that HMRC will accept, so the best approach is always to file well before the deadline.
“But I Don’t Owe Any Tax… Do I Still Get Fined?”
Yes. The penalty applies whether or not you owe any tax. HMRC expects every registered individual to file their return if required, regardless of their income level or tax bill.
Failing to file doesn’t just cost money, it also increases your risk of future investigations and additional compliance checks.
Fines Don’t Go Away
If you’re self-employed, the penalties are your personal liability, even if you stop trading later on. That means you’re still responsible for paying them. They don’t disappear when your business closes.
This can also affect your credit record and your ability to register a new business in the future, so it’s worth keeping on top of your filings every year.
How to Avoid the Stress
Getting your Self-Assessment filed on time doesn’t have to be difficult. The key is preparation.
Here are a few tips to stay ahead of the deadline:
Gather your records early, including invoices, receipts, and expense details.
Make sure your bookkeeping is up to date so you’re not scrambling in January.
Use accounting software to keep your figures organised throughout the year.
Set reminders for key tax dates.
Ask your accountant for help well before the deadline.
At Rhombus Accounting, we help business owners and self-employed individuals stay compliant and stress-free during tax season. Whether you need help filing your return or understanding what you can claim, our team can take care of it for you.
The Bottom Line
Missing the Self-Assessment deadline is expensive and easily avoided.
HMRC’s penalty system adds up fast, and the fines don’t go away, even if you no longer trade. Save yourself the stress and money by getting your return sorted now.
File before 31 January 2026, and keep your hard-earned money in your pocket where it belongs.
Meet Lewis
Lewis is a professional accountant and founder of Rhombus Accounting. He regularly shares his knowledge and best advice here on his blog and on other channels such as LinkedIn.
Book a call today to learn more about what Lewis and Rhombus Accounting can do for you.
