Did You Miss Your Self Assessment Deadline? Late Penalties & Payment Options Explained

If you missed the 31 January Self Assessment deadline, you are not alone. This year, an estimated 1 million people have missed the deadline and are now facing an immediate £100 late filing penalty. That figure is slightly lower than last year, when approximately 1.1 million taxpayers were subject to the same fine.

So, what will happen now? Below is a breakdown of what happens when someone misses the deadline, what penalties apply and what steps taxpayers can take to reduce further damage.

What Are the Penalties If You Miss the Self Assessment Deadline?

Unless you have a reasonable excuse or have made an arrangement with HMRC, penalties for filing late begin immediately and increase over time.

The charges are as follows:

In addition to filing penalties, there are also fines for paying late. These are charged at 5% of the unpaid tax after 30 days, 6 months and 12 months.

Interest is also added to any unpaid balance from the first day the payment becomes overdue. HMRC’s current interest rate is 7.75%, which is calculated as the Bank of England base rate plus 4%.

What If You Cannot Pay You Tax Bill?

If you cannot afford to pay your tax bill right now, contact HMRC immediately. Leaving your taxes unattended can lead to further penalties and enforcement action.

HMRC may allow taxpayers to apply for a Time to Pay arrangement, which spreads the cost over multiple instalments. While this can ease immediate financial pressure, it is important to note that interest continues to be charged on the outstanding balance.

Taxpayers may be able to set up a Time to Pay arrangement without speaking to HMRC directly if:

•  Their bill is under £30,000
• The arrangement is set up within 60 days of the 31 January deadline
• There are no other outstanding HMRC debts

In cases other than these, taxpayers will need to contact the Payment Support Service on 0300 200 3835. HMRC considers these cases individually rather than applying a standard repayment timeframe.

Can You Appeal Mistakenly Applied Penalties?

If you believe a penalty is incorrect, or you have a valid reason for filing late, it is possible to submit a formal appeal to HMRC.

HMRC accepts appeals where taxpayers can demonstrate a reasonable excuse, such as:

• Bereavement, such as the death of a close relative or partner shortly before the deadline
• Serious illness, including an unexpected hospital stay or major health issue
• Mental health difficulties, where a condition affected the ability to meet obligations
• System failures, such as HMRC online services being unavailable or rejecting submissions
• Software issues, such as tax software or a computer failure during preparation
• Registration delays, including applying for a PIN, User ID or password in time but receiving it too late
• Lost records, due to theft, fire, flooding or similar events
• Postal disruption, including unexpected delays caused by incidents such as fire, flood or prolonged industrial action, provided the return was posted in good time

Recent HMRC data shows that between 31 March and 30 September 2025, the tax authority received 32,258 appeals against late-filing and late-payment penalties. Taxpayers won 20,076 of those cases, showing appeals can succeed where the excuse is supported by clear evidence.

How to Appeal an HMRC Penalty

Generally, taxpayers have 30 days from the date of the penalty notice to submit an appeal. If the appeal is submitted late, HMRC will expect an explanation for the delay.

1. File Your Return First

HMRC will not consider an appeal until the outstanding tax return has been submitted. Even if payment is not possible yet, filing the return immediately is essential because it stops further late-filing penalties from building up.

2. Gather Your Evidence

To successfully appeal, you will need to show evidence that supports your reason for missing the deadline. This could include medical letters, hospital records, a death certificate, police reports or screenshots of HMRC website errors.

HMRC largely bases appeal decisions on the strength of the supporting evidence, so it is important to collect as much relevant documentation as possible.

3. Submit Your Appeal

The easiest way to appeal is through your Government Gateway account. When submitting the appeal, you will normally need to include:

• The date the penalty was issued
• The date you filed your Self Assessment Tax Return
• Details of your reasonable excuse

After submitting the appeal online, you should remain on the page until you see a confirmation message. This confirms the appeal has been received and will also indicate when HMRC expects to respond.

Taxpayers can also appeal by post. If the penalty arrives by letter, HMRC usually includes an appeal form. Alternatively, taxpayers can download the SA370 appeal form, complete it and send it to HMRC along with a supporting letter.

If no form is available, a signed letter explaining the situation is also acceptable.

Conclusion

Missing the Self Assessment deadline is an unfortunate thing but it is not the end of the road. While penalties begin immediately and escalate over time, there are clear steps taxpayers can take to limit the financial impact. Filing the return as soon as possible, even if payment cannot be made straight away, is the single most important action to stop further late-filing penalties.

The key is not to ignore the problem. Acting quickly, engaging with HMRC early and keeping clear records can significantly reduce stress, costs and the risk of enforcement action. If you are unsure of your position or need help dealing with HMRC, seeking professional advice early can make a meaningful difference.