SA370: How to Appeal a Self Assessment Late Filing or Late Payment Penalty

This guide follows GOV.UK's Self Assessment penalty appeal guidance, its tax appeals guide and the Self Assessment penalties page, as of October 2026. It's for individuals with a penalty notice in front of them.

SA370, SA371 or online

HMRC's guidance gives you a tool to check how to appeal an individual or partnership Self Assessment penalty. From there you can either make the appeal online or download SA370, or SA371 for a partnership, and appeal by post.

Before you start, gather this

• The date the penalty was issued, from your penalty notice.
• The date you filed your Self Assessment tax return, if you've filed it.
• The date you paid your tax, if you've paid it.
• Details of your reasonable excuse for filing late or paying late.

If you didn't need to send a return at all, you don't need a reasonable excuse. You can ask HMRC to cancel the penalty because you didn't need to file, which is a different request from an appeal.

The 30-day deadline

GOV.UK says you usually have 30 days from the date your penalty was issued to contact HMRC or make an appeal. If you miss that, you'll need to give a reason for the delay as well as your reason for the penalty, and the same reasonable excuse test applies to the missed deadline.

What counts as a reasonable excuse

A reasonable excuse is something that stopped you meeting a tax obligation for a valid reason. HMRC's examples include:

• Your partner or another close relative died shortly before the deadline.
• An unexpected stay in hospital, or a serious or life-threatening illness.
• Your computer or software failed while you were preparing your online return, or HMRC's online services had problems.
• A fire, flood or theft stopped you completing the return.
• Postal delays you couldn't have predicted.
• Delays related to a disability or mental illness you have.
• You were unaware of or misunderstood your legal obligation, or you relied on someone else to send your return and they didn't.

Whatever the excuse, you're expected to send the return or payment as soon as you're able to once it's over.

What won't be accepted

• Your cheque bounced or a payment failed because you didn't have enough funds.
• You found the HMRC online system too difficult to use.
• You didn't get a reminder from HMRC.
• You made a mistake on your tax return.

If computer problems stopped you filing or paying, include the date you tried and the details of any system error message.

Should you pay the penalty while you appeal?

HMRC suggests you consider paying it. If you don't pay and the appeal is rejected, you'll owe interest on the penalty from the date it was due until you pay. If the appeal succeeds, HMRC repays what you've paid with interest from the date you paid, as long as you've no other tax outstanding. The tax appeals guide also says that if you've appealed against a penalty, you won't have to pay it until the appeal's settled.

The penalties you might be appealing

As of October 2026, GOV.UK lists an initial £100 penalty for a late return, then daily penalties of £10 a day after 3 months up to £900, and further charges after 6 and 12 months of 5% of the tax due or £300, whichever is greater. Paying late brings penalties of 5% of the unpaid tax at 30 days, 6 months and 12 months. Our guide to the late tax return penalty walks through how those add up, and the Self Assessment deadlines page shows the dates they run from.

After you appeal

1. HMRC considers the appeal and tells you its decision. GOV.UK has a page on when to expect a reply.
2. If HMRC doesn't change its decision, you'll be offered a review by a different officer who wasn't involved. You can also ask for one at any time after appealing.
3. Reviews usually take 45 days, and the officer will contact you if it'll take longer. They'll uphold, vary or cancel the penalty.
4. If you disagree with the review, you can usually appeal to the tax tribunal within 30 days of the review result letter.

Writing the excuse

Keep it short and dated. Say what happened, when it started, when it ended and when you filed or paid afterwards. If you relied on someone else, such as an accountant, say who and what you'd asked them to do. If it was an illness or a hospital stay, give the dates. HMRC's guidance stresses the timeline, because you're expected to put things right as soon as the problem's over.

If you don't have the appeal form and you're appealing a different direct tax penalty by letter, GOV.UK says to send a signed letter to the HMRC office for your return, explain why it was late with dates, and include your name and your Unique Taxpayer Reference.

The verdict

If you've got a late filing or late payment penalty and a reason that fits HMRC's list, appeal within 30 days, online or on SA370. Give dates, keep the explanation factual, and file the overdue SA100 return as soon as you can, because the later penalties are triggered by how long the return stays outstanding.

Frequently asked questions

What is form SA370?

It's the HMRC form to appeal against a Self Assessment late filing or late payment penalty by post. Partnerships use SA371.

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

GOV.UK says you usually have 30 days from the date the penalty was issued. If you miss it, you'll need to give a reason.

Can I appeal a Self Assessment penalty online?

Yes. HMRC's appeal tool lets you appeal online or download SA370 or SA371 to appeal by post.

Is not getting a reminder a reasonable excuse?

No. GOV.UK says not getting a reminder from HMRC won't be accepted as a reasonable excuse.

What happens if HMRC rejects my SA370 appeal?

You'll be offered a review by another officer, and if you disagree with that, you can usually appeal to the tax tribunal within 30 days.