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Self Assessment

Appeal an HMRC late filing penalty: online, on form SA370 or by letter

There are three ways to appeal a late filing penalty: online, by post on form SA370 (HM Revenue and Customs’ paper appeal form), or by letter. Which one GOV.UK offers depends on your answers, and the 30-day clock runs from when the notice was issued, not the day it arrives. Here is how to choose, what to send and what to check first.

Independent guide, not governmentReviewed by Liam Humphreys on Last updated Last checked 10 sources11 min readHow this guide was made, including our use of AI

Contents

Status at 27 October 2026: the 2025 to 2026 return is due 31 January 2027

GOV.UK says the online return and the tax are due by 11:59pm on 31 January 2027. HM Revenue and Customs (HMRC) issues late filing penalties after that date, from February. We walked through GOV.UK’s “check how to appeal” tool on 27 October 2026, as an individual, and describe what it said. It can change, so check it before you rely on this.

The short version

  • Three routes. Make the appeal online, send form SA370 by post (SA371 for a partnership), or send a signed letter.
  • GOV.UK’s tool decides which you are offered. When we tried it as an individual with a 2025 to 2026 penalty, it offered an online appeal for each of the seven penalty types (the £100, the 3, 6 and 12-month filing penalties and the three late payment penalties), once we said we had filed. The tool did not limit online appeals to the £100 penalty.
  • You usually have 30 days. HMRC’s manual says the clock runs from the date HMRC posts the notice, not the date you get it, and form SA370 says to count from the date shown on the front of the notice. A late appeal can still be accepted if you had a reasonable excuse for the delay.
  • File your return first. GOV.UK’s tool warns that HMRC may not be able to progress your appeal until you have.
  • Appeal each penalty. Form SA370 has a separate box for each one, and in the Berry case below the tribunal could not hear a penalty that was issued after the appeal reached it.
A man with glasses reads a letter at a rain-streaked kitchen window table, an opened envelope beside him.
Illustration. AI-generated image. About our images

Before you start

GOV.UK says to have these ready:

  • the date the penalty was issued, from the top of the penalty notice;
  • the date you filed your return, if you have;
  • the date you paid your tax, if you have; and
  • the details of your reasonable excuse, with dates.

On paper you will also need your Unique Taxpayer Reference (UTR) and, if you know it, your National Insurance number. Our guide to reasonable excuse examples shows what HMRC’s manual accepts.

Online, SA370 or letter: how to choose

The three ways to appeal an HMRC Self Assessment late filing penalty
RouteHow it worksWorth knowing
OnlineFrom the GOV.UK tool you sign in with your HMRC details (the tool says that if you do not have sign-in details you will be able to create them). The tool says HMRC “will get the appeal straight away”.In our walk-through, an individual was offered this for every penalty type for 2025 to 2026. The tool says you cannot appeal online for tax years earlier than 2021 to 2022.
Form SA370 by postPrint it, fill it in and post it to Self Assessment, HM Revenue and Customs, BX9 1AS, within 30 days of the date shown on the front of your penalty notice, which is what the form itself says.It has a box for each penalty (£100, 3, 6 and 12-month filing, and 30-day, 6-month and 12-month payment), the notice date and amount, a tick list of reasons and a free-text box. There is a space to say you sign as an agent or executor.
Form SA371 by postThe partnership version of the form.The tool asks whether you are the nominated partner.
Signed letterGOV.UK says that if you have no appeal form you can send a signed letter to the HMRC office for your return.Give your name, your UTR and why the return or payment was late, with dates.

SA370’s tick list covers ill health, postal issues, fire, flood or other natural disasters, did not receive the return, theft or crime, bereavement, information technology difficulties and “other acceptable excuse”. For “other” it asks for as much information as you can give, including dates and, where possible, evidence.

Two other points on the route.

  • The appeal must be in writing. HMRC’s Appeals, Reviews and Tribunals Guidance says an appeal must be by written notice, and that a caller who tries to appeal by phone should be told to put it in writing. Ringing HMRC is not the same as appealing. An HMRC SA370 leaflet quoted in Berry speaks of contacting HMRC “online or in writing” about an appeal, which fits the online route.
  • You can appoint someone. GOV.UK says you can appoint someone else to deal with HMRC on your behalf.

If you want to use the tool, start from GOV.UK’s Appeal a Self Assessment penalty for late filing or late payment page.

File first, and what happens if you have not

GOV.UK’s tool lets you say you have not filed, but the question it then asks says: “Make sure you have submitted your return as we may not be able to progress your appeal until you have done so. We recommend filing online to avoid further penalties.” Form SA370 says to send your return and pay any tax you owe now to avoid further penalties.

The reason is in the law. A reasonable excuse has to last until you file, or you must have filed without unreasonable delay after it ended (Finance Act 2009, Schedule 55, paragraph 23). In Berry v HMRC [2026] UKFTT 1451 (TC) HMRC’s letters said it could not agree a reasonable excuse while the return was outstanding, and the tribunal repeated that an excuse has to last until the return is filed. The taxpayer in that case filed 537 days after the paper deadline and lost.

The 30 days

  • From when the notice is issued. HMRC’s manual says it is the date HMRC posts the decision notice, not the date the customer receives it, while form SA370 says to count from the date shown on the front of the notice. Notices can take time: in Berry a penalty notice dated 18 February 2025 reached the taxpayer on 10 March 2025.
  • If you are late. The law says HMRC must accept a late appeal if you had a reasonable excuse for not appealing in time and you appealed without unreasonable delay after the excuse ended (Taxes Management Act 1970, section 49), and you must ask in writing. HMRC’s manual gives sickness and exceptional postal delays as examples, and says an agent’s failure and being busy are not reasonable excuses for a late appeal.
  • If HMRC refuses. You can ask the tribunal. HMRC’s manual says the tribunal is not limited by the reasonable excuse conditions and can accept a late appeal if it thinks it is in the interests of justice. The First-tier Tribunal asks how long the delay was, why it happened and then weighs all the circumstances, including prejudice to each side, following Martland v HMRC [2018] UKUT 178 (TCC), as summarised in Monaghan.

Check the penalty is right before you argue an excuse

A reasonable excuse is not your only argument. Before it comes into play, HMRC has to prove the penalty is due.

  • Did HMRC have to send you a notice to file? A late filing penalty depends on HMRC having given you a notice to file a return. In Monaghan v HMRC [2026] UKFTT 1029 (TC), decided on the papers, HMRC produced no notice to file for 2019 to 2020. The tribunal allowed the appeal against penalties of £1,600, even though the appeal to HMRC was very late. It relied on the Upper Tribunal’s statement in Rogers v HMRC [2019] UKUT 406 (TCC) that HMRC must prove a notice was served, and on Marano v HMRC [2024] EWCA Civ 876, where the Court of Appeal recorded that it was common ground that a taxpayer with no notice to file cannot be liable for a late filing penalty.
  • A caution. Section 12D of the Taxes Management Act 1970, inserted retrospectively by Finance Act 2019, says that where you deliver a return without having been given a notice to file and HMRC treats it as made in response to one, a notice is treated as given on the day you delivered it. In Wals v HMRC [2025] UKFTT 1331 (TC) the tribunal said a voluntary return is treated as made in response to a valid notice to file, so HMRC not proving a notice did not cancel the penalties. Not having had a notice may therefore not help if you filed on your own. Monaghan, also a First-tier decision, did not mention section 12D.
  • Did HMRC prove it served the penalty notices? In Walker v HMRC [2023] UKFTT 865 (TC) HMRC said it had served notices electronically because she was signed up to paperless contact. The tribunal was not satisfied HMRC had proved that and allowed the appeal against penalties of £1,300.
  • Did you need to file at all? GOV.UK says you can ask HMRC to cancel a penalty if you do not need to send a Self Assessment return, and links to its page on how to stop. Berry shows the limits: income under the personal allowance did not remove the need to file once HMRC had sent a notice to file.

Our reading: look for any notice to file or penalty notice you received, and check what is in your online account, before you decide how to put your case. These are separate arguments from a reasonable excuse, and you can raise them together.

What to write

HMRC’s manual says to explain not only what your excuse is but how it stopped you meeting the obligation. Give dates, in order: the deadline and the penalty notice, what happened and when it began and ended, how it stopped you filing, when and how you filed, and what evidence you have. HMRC’s manual says staff must listen to your explanation and, if they do not accept it, tell you and give you a chance to add arguments or evidence before they decide.

Paying while you appeal

GOV.UK says to pay a penalty within 30 days of the notice, but it gives two linked statements for people who appeal. On the page for appealing a penalty it says you “should consider paying the penalty if you appeal”: if your appeal is rejected you pay interest on the penalty from the date it was due, and if it succeeds HMRC repays you with interest (if you have no other outstanding tax). On the page about delaying payment it says that if you have appealed against a penalty you will not have to pay until your appeal is settled. When you pay, GOV.UK says to use your 11-character reference: your UTR followed by the letter K.

After you appeal

  • HMRC looks again. HMRC’s manual says the caseworker will consider the appeal and, if they do not accept it, write with their current view and offer a review. GOV.UK has a tool to check when you can expect a reply.
  • Review or tribunal. If HMRC does not change its decision, GOV.UK says you will be offered a review. You have 30 days from the date of the offer to accept it or appeal to the tribunal. You can also ask for a review at any time after appealing. GOV.UK says reviews usually take 45 days.
  • Tribunal. For direct taxes you must appeal to HMRC first. After a review you can usually appeal to the First-tier Tribunal within 30 days of the review result letter. GOV.UK says you do not have to pay upfront if you are appealing a penalty.
  • One appeal per penalty. Each penalty has its own notice, and SA370 has a box for each. In Berry the taxpayer appealed to the tribunal on 3 February 2026. The 12-month penalty was issued on 17 February 2026, after that appeal, so the tribunal said it had no power over it. HMRC accepted he had a reasonable excuse for thinking he had appealed it and said it would process an appeal.

If you get a later penalty, appeal that one too. Our guide to daily, 6-month and 12-month penalties explains when each is issued.

Our kit

The HMRC Self Assessment Penalty Appeal Pack has a decision checklist, a timeline worksheet with your 30-day dates, letter templates for common excuses, a review letter and a tracker. It does not send anything to HMRC and does not guarantee a result. You can appeal without it.

Frequently asked questions

Can I appeal by phone?

HMRC’s manual says an appeal must be in writing and that someone who phones to appeal should be told that. Use the online service, form SA370 or a letter.

Can I appeal before I have filed my return?

GOV.UK’s tool lets you say you have not filed, but warns that HMRC may not be able to progress the appeal until you do. File first, as soon as you can.

Do I appeal the £100 and the daily penalties separately?

Yes. SA370 has a separate box for each penalty, and each penalty has its own notice. Appeal each when you receive its notice.

The penalty notice says I have 30 days. When does that start?

HMRC’s manual says it runs from the date HMRC posts the notice, not the date you receive it, and form SA370 says to count from the date shown on the front of the notice. Check that date, not the day it arrived.

Can an accountant appeal for me?

GOV.UK says you can appoint someone to deal with HMRC on your behalf, and SA370 has a space to say you sign as an agent or executor. If your excuse is that you relied on an accountant, see our guide on agents and reasonable excuse.

Sources

Last checked 27 October 2026.

Changes to this guide

  • 27 October 2026: Published.

This guide is general information written from the official sources listed above and checked on 27 October 2026. It is not legal, tax or financial advice, and Plainfiles is not endorsed by any government body. Rules change, so check the linked official pages for your own situation. Written and designed by Plainfiles with the help of artificial intelligence (AI) tools, then checked against the official legislation and guidance listed in the sources. How we write and check our guides.