To appeal a Self Assessment penalty, you normally have 30 days from the date on the penalty notice. You can appeal online or on form SA370, and you must show a reasonable excuse, such as a serious illness, a bereavement or an HMRC system failure, and that you filed or paid as soon as the problem ended. If HMRC refuses, you can ask for an independent review or appeal to the tax tribunal.

For the 2025/26 tax year, the online return and payment are due by 31 January 2027, and a late return triggers an automatic £100 penalty even if you owe no tax. This guide sets out the late penalties that apply, what HMRC accepts as a reasonable excuse, how to appeal step by step and a worked example.

Self Assessment Late Penalties for 2025/26

If you are not yet in Making Tax Digital, the existing penalty rules apply to your 2025/26 return.

How late	Late filing penalty
1 day	£100 fixed penalty
3 months	£10 a day for up to 90 days (maximum £900)
6 months	5% of the tax due or £300, whichever is higher
12 months	A further 5% of the tax due or £300, whichever is higher (more if information was deliberately withheld)

How late	Late payment penalty
30 days	5% of the tax unpaid
6 months	A further 5% of the tax still unpaid
12 months	A further 5% of the tax still unpaid

HMRC also charges late payment interest from the due date until you pay. Landlords and sole traders who are in Making Tax Digital from 2026/27 move to a points-based system, so check which rules apply to you.

What Counts as a Reasonable Excuse?

Before you appeal a Self Assessment penalty, check your reason fits HMRC’s test. A reasonable excuse is something that stopped you meeting the deadline that you could not reasonably have foreseen or avoided. HMRC’s own examples include:

• Your partner or another close relative died shortly before the deadline
• An unexpected stay in hospital
• A serious or life-threatening illness, or delays related to a disability or mental illness
• Your computer or software failed while you were preparing your online return
• Problems with HMRC online services
• A fire, flood or theft that stopped you completing your return
• Postal delays you could not have predicted

HMRC does not accept these as reasonable excuses:

• You did not receive a reminder from HMRC
• You found HMRC online services too difficult to use
• You made mistakes on your tax return
• A payment failed because there was not enough money in your account

Whatever the excuse, you must file or pay as soon as you are able once the problem has passed. A delay of several weeks after you recovered is likely to make HMRC reject the appeal.

How to Appeal a Self Assessment Penalty Step by Step

1. Check the penalty notice. Note the date it was issued, the penalty amount and the tax year. You usually have 30 days from that date to appeal.
2. File the return and pay the tax if you have not already. This stops further daily and percentage penalties building up.
3. Gather evidence of your excuse with dates, such as hospital letters, a death certificate or screenshots of error messages from HMRC online services.
4. Submit the appeal online through your HMRC account, or on form SA370 (SA371 for partnerships). Without a form, you can write a signed letter with your name, UTR, the reason and the dates.
5. Consider paying the penalty while you wait. If the appeal succeeds, HMRC repays it with interest.
6. If HMRC refuses, ask for an independent review by another HMRC officer, or appeal to the First-tier Tribunal (Tax).

Most people only need to appeal a Self Assessment penalty once. Our guide to the Self Assessment deadline for 31 January 2027 explains how to avoid needing an appeal in the first place.

Worked Example: Penalties on a Late 2025/26 Return

This is an illustrative example, not a real client. A self-employed taxpayer who is not in Making Tax Digital owes £4,000 for 2025/26. The return and payment were due on 31 January 2027, but both are made on 15 August 2027.

Penalty	Calculation	Amount
Initial late filing penalty	Fixed	£100
Daily penalties from 1 May 2027	£10 × 90 days	£900
6-month late filing penalty	5% of £4,000 = £200, minimum £300	£300
30-day late payment penalty	5% of £4,000	£200
6-month late payment penalty	5% of £4,000	£200
Total penalties		£1,700 plus interest

Now suppose the taxpayer was in hospital from mid-January to the end of March 2027, but then waited until August to file. HMRC may accept the hospital stay as a reasonable excuse for missing the January deadline, but is unlikely to accept it for the four and a half months after recovery. Filing promptly in early April would have given a much stronger appeal and avoided most of the penalties.

What If You Cannot Pay?

When you appeal a Self Assessment penalty, the appeal does not cover the tax itself. If you cannot pay in full, file on time anyway to avoid the filing penalties, and contact HMRC about a Time to Pay arrangement. See what to do if you cannot pay your tax bill and how to avoid late payment penalties. If you have already missed the deadline, our missed deadline rescue plan sets out the first steps.

Frequently Asked Questions

How long do I have to appeal a Self Assessment penalty?

Usually 30 days from the date on the penalty notice. If you miss that, you can still ask HMRC to accept a late appeal, but you must explain why you could not appeal in time.

What counts as a reasonable excuse for a late tax return?

Examples HMRC accepts include the death of a partner or close relative shortly before the deadline, an unexpected hospital stay, serious illness, HMRC online service problems, fire, flood or theft, and unforeseeable postal delays. You must then file as soon as you are able.

Is not getting a reminder from HMRC a reasonable excuse?

No. HMRC does not accept not receiving a reminder, finding the online system too difficult or mistakes on your return as reasonable excuses.

Should I pay the penalty while I appeal?

HMRC suggests considering it. If your appeal fails you will owe interest from the due date, and if it succeeds HMRC repays the penalty with interest, provided you have no other tax outstanding.

Can I appeal if I did not need to file a tax return?

You can ask HMRC to cancel the penalty if you no longer need to be in Self Assessment, for example because your income is now all taxed through PAYE.

Get Help to Appeal a Self Assessment Penalty

If you need to appeal a Self Assessment penalty, a clear, well-evidenced appeal has the best chance of success. We can file overdue returns, prepare your appeal and deal with HMRC on your behalf through our Self Assessment service and tax return service, for a fixed fee agreed upfront. Call 01204 859315, email [email protected] or book a call.

Official guidance: appeal a penalty, reasonable excuses, check when to appeal a Self Assessment penalty and Self Assessment penalties (GOV.UK).