If you miss the 31 January deadline for filing your Self Assessment tax return, HMRC charges an automatic £100 penalty. That is the starting point, not the full picture. The penalties escalate quickly the longer you delay, and they can reach thousands of pounds for returns filed more than 12 months late.
This guide covers the complete HMRC penalties self assessment structure for the 2025/26 tax year, including the new penalty system that applies from the 2024/25 return onwards. We explain the exact amounts, when interest kicks in, and how to appeal if you have a reasonable excuse.
The Three-Day Grace Period
The filing deadline for online Self Assessment returns is midnight on 31 January following the end of the tax year. For the 2024/25 tax year (ending 5 April 2025), the deadline is 31 January 2026.
HMRC does not issue a penalty immediately on 1 February. You get a three-day grace period. If you file on 1, 2, or 3 February, there is no penalty. The automatic £100 penalty only applies to returns filed on or after 4 February.
This is a long-standing administrative concession. It is not written into law, but HMRC applies it consistently. Do not rely on it. File before 31 January.
Standard Late Filing Penalties (Returns Due After 2022/23)
For returns covering the 2024/25 tax year and later, HMRC uses a two-tier penalty system. The first tier is fixed penalties. The second tier is tax-geared penalties for longer delays.
Here is the fixed penalty structure:
- 1 day late (4 February): £100 fixed penalty
- 3 months late (1 May): £10 per day for up to 90 days (£900 maximum)
- 6 months late (1 August): £300 or 5% of the tax due (whichever is higher)
- 12 months late (1 February): £300 or 5% of the tax due (whichever is higher)
The daily penalties run from the day after the three-month point. That means from 1 May 2026, you incur £10 per day until you file or reach 90 days. The maximum daily penalty is £900.
At six months late, you face an additional penalty of £300 or 5% of the tax due. HMRC charges whichever is higher. If your tax bill is £10,000, the 5% penalty is £500, so you pay £500 instead of £300.
At twelve months late, the same calculation applies again. A further £300 or 5% of the tax due.
So the maximum fixed penalties for a return filed more than 12 months late are £1,600 (£100 + £900 + £300 + £300), plus any tax-geared penalties that apply.
Tax-Geared Penalties at 12 Months
If you file more than 12 months late, HMRC can also charge a tax-geared penalty based on the amount of tax you owe. This applies where HMRC believes you deliberately withheld information or concealed income.
The tax-geared penalty ranges from 30% to 100% of the tax due, depending on whether the late filing was careless or deliberate. Most straightforward late filings do not attract these penalties, but they exist for serious non-compliance.
Late Payment Penalties
Filing late and paying late are separate issues. You can file on time but pay late, and vice versa.
If you pay your tax bill after the 31 January deadline, HMRC charges interest on the outstanding amount. The late payment interest rate for 2025/26 is 7.25% (it changes quarterly based on the Bank of England base rate).
In addition to interest, HMRC charges a late payment penalty if you have not paid after 30 days. The structure is:
- 30 days late: 5% of the unpaid tax
- 6 months late: 5% of the unpaid tax (additional)
- 12 months late: 5% of the unpaid tax (additional)
So the maximum late payment penalty is 15% of the unpaid tax, plus interest. These penalties apply on top of any late filing penalties.
Penalties for Inaccurate Returns
If you file on time but submit an inaccurate return, HMRC can charge penalties based on the amount of tax underpaid. The penalty percentage depends on whether the inaccuracy was:
- Careless (not enough care taken): 0% to 30% of the tax underpaid
- Deliberate but not concealed: 20% to 70%
- Deliberate and concealed: 30% to 100%
If you voluntarily tell HMRC about the inaccuracy before they find it, the penalty is reduced. This is called "unprompted disclosure". If HMRC discovers the error first, the reduction is smaller ("prompted disclosure").
How to Appeal a Late Filing Penalty
You can appeal a late filing penalty if you have a reasonable excuse. HMRC defines a reasonable excuse as something that stopped you filing on time that was outside your control.
Examples that HMRC typically accepts:
- Serious illness or hospitalisation close to the deadline
- Death of a close family member
- Fire, flood, or theft destroying your records
- Computer or software failure that could not be prevented
- Postal delays that were unexpected and unavoidable
Examples that HMRC typically rejects:
- Being too busy with work
- Not knowing about the deadline
- Relying on someone else who let you down (agent or accountant)
- Not having the money to pay the tax
- Problems with HMRC's online system (unless you have evidence)
You can appeal online through your HMRC account or by writing to HMRC. You must appeal within 30 days of receiving the penalty notice. If HMRC rejects your appeal, you can take it to the Tax Tribunal.
What Happens If You Do Not File at All
If you never file a return and HMRC has to estimate your tax liability, they issue a "determination". A determination is HMRC's best guess of what you owe, and it is legally enforceable. You cannot appeal a determination. The only way to replace it is to file the actual return, even if it is years late.
If you owe tax and do not file, HMRC can take enforcement action including:
- County Court Judgments (CCJs)
- Bailiff action
- Bankruptcy proceedings
- Charges against your property
For the most serious cases, HMRC can prosecute for failure to notify chargeability to tax. This is rare but carries a potential prison sentence.
Practical Steps If You Have Missed the Deadline
If you missed the 31 January deadline, do the following in order:
- File your return as soon as possible. Every day counts for the daily penalties.
- Pay the tax you owe, or set up a Time to Pay arrangement with HMRC if you cannot pay in full.
- Check whether you have a reasonable excuse to appeal the penalty.
- If you do, submit your appeal within 30 days of the penalty notice.
Time to Pay arrangements are available online for debts up to £30,000. You can set one up through your HMRC account without speaking to anyone. For larger debts, you need to call HMRC's Payment Support Service on 0300 200 3835.
How We Help
As ICAEW qualified accountants, we deal with HMRC penalty appeals regularly. If you have a reasonable excuse, we can help you prepare the evidence and submit the appeal. If you are simply late, we can help you file and pay quickly to minimise the penalties.
If you are a limited company director filing a Self Assessment return alongside your company accounts, the deadlines are the same. The penalty structure applies identically to individuals and company directors.
For sole traders and partnerships, the Self Assessment return includes your business income pages (SA103 for sole traders, SA800 for partnerships). The same penalty rules apply to the whole return.
If your turnover is approaching the VAT registration threshold (£90,000), or if you are already VAT registered, late filing of your Self Assessment is separate from any VAT penalties. They are different obligations with different penalty systems.
The 2025/26 Filing Season
The 2024/25 tax year ends on 5 April 2025. The filing deadline for online returns is 31 January 2026. Paper returns must be filed by 31 October 2025.
If you use accounting software like Xero, FreeAgent, or QuickBooks, most of them integrate with HMRC's systems for Making Tax Digital for Income Tax (MTD for ITSA). From April 2026, MTD for ITSA becomes mandatory for sole traders and landlords with qualifying income over £50,000. From April 2027, it drops to £30,000. From April 2028, it drops to £20,000.
MTD for ITSA requires you to file quarterly updates to HMRC, not just an annual return. The penalty system for MTD is different. Late quarterly submissions attract points-based penalties rather than the fixed £100 starting point. But the annual final declaration still uses the standard late filing penalties.
Summary of Key Numbers for 2025/26
- Filing deadline: 31 January 2026
- First penalty: £100 from 4 February 2026
- Daily penalties: £10 per day from 1 May 2026 (max £900)
- 6-month penalty: £300 or 5% of tax due
- 12-month penalty: £300 or 5% of tax due
- Late payment interest: 7.25% (subject to change)
- Late payment penalties: 5% at 30 days, 5% at 6 months, 5% at 12 months
If you need help with a late return, a penalty appeal, or setting up a Time to Pay arrangement, contact us. We work with clients across the UK, from sole traders in Bristol to limited companies in Manchester and everything in between.
For more on Self Assessment basics, see our fundamentals guide. For specific guidance on filing as a sole trader, see our sole trader and self employment blog.