How to Appeal a CT600 Late Filing Penalty from HMRC

How to Appeal a CT600 Late Filing Penalty from HMRC

Got a penalty notice from HMRC for filing your CT600 late? You might be able to get it cancelled. HMRC accepts appeals based on reasonable excuse, and more succeed than you might think.

The CT600 Penalty Structure

Before appealing, understand what you've been charged:

These are per return and can stack. A CT600 that's 12+ months late incurs at least £1,200 in penalties — even if the company owes zero tax.

Important: The 3-year rule

If your CT600 is filed more than 3 consecutive periods late, the first two penalties increase from £100 to £500 each.

What Counts as a Reasonable Excuse?

HMRC defines a reasonable excuse as "an unexpected or unusual event, either unforeseeable or beyond your control, that prevented you from filing on time."

Excuses HMRC typically ACCEPTS ✅

• Serious illness or hospitalisation — you or a close family member
• Bereavement — death of a close relative near the deadline
• Fire, flood, or natural disaster — affecting your records or premises
• HMRC system failure — if HMRC's own service was down when you tried to file
• Postal delay — if you posted a paper return in good time (rare for CT600)
• Threat of violence — circumstances preventing compliance
• Mental health crisis — documented mental health conditions

Excuses HMRC typically REJECTS ❌

• "I didn't know I had to file" — ignorance is not a reasonable excuse
• "My accountant didn't file on time" — you're responsible, not your accountant
• "The company was dormant" — dormant companies still need to file nil returns
• "I was busy / travelling" — predictable absences aren't unexpected
• "I couldn't find my UTR" — you should have requested it in advance
• "I didn't receive a reminder" — HMRC is not obliged to remind you

The grey area

Some excuses depend on circumstances:

• Software failure: If your filing software genuinely failed near the deadline and you can prove it, this may succeed
• COVID-related issues: HMRC was lenient during 2020-2021 but this is no longer automatic
• Reliance on a third party: If someone else (not an accountant) was supposed to handle it and let you down, it depends on whether you took reasonable steps to check

How to Appeal: Step by Step

Step 1: Check your penalty notice

The penalty notice (SA371 or similar) tells you:

• What the penalty is for
• The amount
• The deadline to appeal (30 days from the date of the notice)
• How to appeal

Step 2: Decide: appeal or pay

If you have a genuine reasonable excuse, appeal. If you were simply late with no good reason, it's usually better to pay — unsuccessful appeals waste time and the penalty remains.

Step 3: Appeal online or by post

Online (fastest):

1. Log into your HMRC business tax account
2. Go to Corporation Tax
3. Find the penalty
4. Select "Appeal"
5. Enter your reason and any supporting evidence dates

By post: Write to:

Corporation Tax Services HM Revenue and Customs BX9 1AX

Include:

• Company name and UTR
• The penalty reference number
• Your reason for the appeal
• Any supporting evidence
• Your contact details

Step 4: Provide evidence

Support your appeal with evidence:

• Medical: Doctor's letter, hospital discharge summary
• Bereavement: Death certificate date
• Disaster: Insurance claim, photos, news reports
• Software: Error screenshots, support tickets
• HMRC system: Screenshots of error messages with timestamps

Step 5: Wait for HMRC's decision

HMRC typically responds within 30-60 days. They'll either:

• Accept your appeal — penalty cancelled
• Reject your appeal — penalty stands, with reasons

What If Your Appeal Is Rejected?

Internal review

You can ask for an internal review by a different HMRC officer who wasn't involved in the original decision. Request this within 30 days of the rejection.

Tribunal

If the internal review also rejects your appeal, you can appeal to the First-tier Tax Tribunal within 30 days. The tribunal is independent of HMRC.

Tribunal costs:

• No fee to apply
• You represent yourself (or hire a representative)
• Usually decided on paper (no hearing needed for simple penalty appeals)
• HMRC must prove the penalty is correct; you must prove you have a reasonable excuse

Success rates

Many penalty appeals succeed at tribunal — especially where HMRC has been rigid about genuine hardship cases. Tribunals take a broader view of "reasonable excuse" than HMRC's initial assessors.

Time Limits

Late appeals

You can appeal after 30 days if you have a good reason for the delay. HMRC and the tribunal can accept late appeals — but the longer you wait, the harder it is to justify.

Tips for a Successful Appeal

1. Be specific

Don't write "I was ill." Write "I was hospitalised from 14 to 28 February 2026 with pneumonia (Dr. Smith, Royal London Hospital, discharge letter attached)."

2. Show the timeline

Demonstrate that:

• Before the event, you intended to file on time
• The event prevented you from filing
• Once the event passed, you filed as soon as reasonably possible

3. File now

If you haven't filed the CT600 yet, file it immediately before appealing. HMRC looks more favourably on appeals where the return has been submitted.

4. Pay any tax owed

If corporation tax is due, pay it. This stops interest accruing and shows good faith. You can still appeal the penalty while paying the tax.

5. Don't admit fault

If you have a reasonable excuse, state it clearly. Don't undermine your appeal by saying "I know I should have filed earlier." Stick to the facts.

Multiple Penalties

If you've received penalties for multiple periods, you can appeal each one. However, if the same excuse applies to all periods, submit one appeal covering all penalties.

Example appeal letter:

Dear Corporation Tax Services,

I am writing to appeal late filing penalties for [Company Name], UTR [number], for the accounting periods ending [dates].

The penalties are: [list reference numbers and amounts]

Reasonable excuse: [Clear, specific description of what happened, when it started, when it ended, and when you filed]

Supporting evidence: [List attached documents]

I filed the outstanding return(s) on [date] and any tax due has been paid.

I request that these penalties be cancelled.

Yours faithfully, [Name, position]

Preventing Future Penalties

1. File early

Don't wait until the deadline. File as soon as your accounts are ready — even months before the deadline.

2. Use filing software

Software like Taxpipe makes filing quick and catches errors before submission. At £59 per return, it's far cheaper than a single penalty.

3. Set calendar reminders

• 6 months before deadline: Start preparing accounts
• 3 months before: Have figures ready
• 1 month before: File the CT600
• Payment date: 9 months + 1 day after year-end (earlier than filing deadline)

4. Register for HMRC email reminders

HMRC can send deadline reminders if you opt in through your business tax account.

Frequently Asked Questions

Can I appeal a penalty if I've already paid it?

Yes. Payment doesn't waive your right to appeal. If the appeal succeeds, HMRC refunds the penalty.

Do I need an accountant to appeal?

No. Most penalty appeals are straightforward and you can handle them yourself. Write a clear letter with evidence.

What if the penalty is for a dormant company?

You can still appeal if you have a reasonable excuse. But "I didn't know dormant companies needed to file" is not a reasonable excuse — you should have been aware of your obligations.

Will appealing delay HMRC enforcement?

While your appeal is being considered, HMRC generally won't take enforcement action on the penalty amount. But you should still pay any corporation tax owed.

How do I avoid this happening again?

File your CT600 with Taxpipe as soon as your accounts are ready. Our guided wizard takes about 15 minutes, and at £59 per return, it costs less than a single late filing penalty.

Don't risk another penalty. File your CT600 now with Taxpipe — 15 minutes, £59, direct HMRC submission.

Related Articles

• CT600 Nil Return: How to File When Your Company Has No Trading Activity
• HMRC Penalties for Late Corporation Tax Filing — Every Tier Explained