Corporation Tax Penalties & Interest Charges

Corporation Tax Penalties & Interest Charges: What Every Director Needs to Know

Getting a penalty notice from HMRC is never pleasant. But if you're a UK limited company director, understanding exactly how corporation tax penalties and interest charges work can save you thousands — and in many cases, you can appeal successfully if you have a reasonable excuse.

This guide covers everything: the penalty structure for late filing and late payment, how HMRC calculates interest, what triggers an enquiry, and step-by-step instructions for making an appeal.

Late Filing Penalties: The CT600 Return

Your company must file its CT600 corporation tax return within 12 months of the end of its accounting period. Miss that deadline, and HMRC's automatic penalty system kicks in immediately.

The CT600 Late Filing Penalty Structure

So if your company owes £10,000 in corporation tax and you file 12 months late, the penalties alone could be:

• £100 + £100 + £1,000 + £1,000 = £2,200

Even if your company owes zero tax, you still face the flat £100 + £100 = £200 in penalties.

The Three-Year Repeat Offender Rule

If your company has filed its CT600 late for three consecutive periods, the flat-rate penalties escalate from £100 to £500 each. That means:

• 1 day late: £500 (not £100)
• 3 months late: another £500 (not £100)

This catches directors who habitually file late, and the jump from £200 to £1,000 in fixed penalties is substantial.

Key Point: Filing and Payment Are Separate

A common misconception is that paying your corporation tax on time means you don't need to worry about the return. Wrong. Filing the CT600 and paying the tax are completely separate obligations with separate deadlines and separate penalties.

• Filing deadline: 12 months after the end of your accounting period
• Payment deadline: 9 months and 1 day after the end of your accounting period

You can pay on time but still get a filing penalty (and vice versa).

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Late Payment Penalties and Interest

Unlike late filing (which triggers flat penalties), late payment of corporation tax primarily incurs interest charges rather than fixed penalties. However, there are scenarios where penalties apply too.

How Late Payment Interest Works

HMRC charges interest on corporation tax paid late from the day after the payment deadline (9 months and 1 day after your accounting period end) until the date you pay.

The late payment interest rate is set by HMRC and tracks the Bank of England base rate plus 2.5%. As of early 2026, this rate is 7.25% per annum — significantly higher than most commercial borrowing rates.

Interest Calculation Example

Suppose your company owes £15,000 in corporation tax with a payment deadline of 1 January 2026, and you pay on 1 April 2026 — 90 days late.

Interest = £15,000 × 7.25% × (90 ÷ 365) = £268.15

HMRC calculates this automatically and will send you a notice showing the interest due. Interest continues to accrue until you pay in full, including interest on the original interest if left long enough.

When Do Actual Payment Penalties Apply?

For most small and medium companies, late payment results in interest charges only. However, HMRC can impose tax-geared penalties in cases of:

• Deliberate underpayment — where you knowingly understated your tax liability
• Failure to notify chargeability — if your company was liable but didn't register for or notify HMRC of its corporation tax liability
• Inaccurate returns — if errors on your CT600 led to underpayment

These penalties are calculated as a percentage of the potential lost revenue (PLR) — the additional tax due:

The range exists because HMRC considers the quality of your disclosure — how much you helped them identify and quantify the error.

Repayment Interest: When HMRC Owes You

If you've overpaid corporation tax, HMRC will pay you repayment interest. However, the repayment interest rate is much lower than the late payment rate — typically the Bank of England base rate minus 1%, with a minimum of 0.5%.

As of 2026, the repayment interest rate is around 3.75%. This asymmetry means it's always better to pay the right amount on time rather than overpay and wait for a refund.

You can learn more about claiming a corporation tax refund in our dedicated guide.

How to Appeal a Corporation Tax Penalty

You have the right to appeal any penalty imposed by HMRC, and a significant percentage of appeals succeed — particularly for first-time offences with genuine reasonable excuses.

What Counts as a Reasonable Excuse?

HMRC defines a reasonable excuse as an unexpected or unusual event that was beyond your control and prevented you from meeting your obligation on time.

Excuses HMRC typically accepts:

• Serious illness or hospitalisation of the person responsible for filing
• Death of a close relative or business partner close to the deadline
• Fire, flood, or natural disaster affecting your business premises or records
• HMRC's own systems being unavailable (with evidence)
• Postal delays (for paper returns, though electronic filing is now standard)
• Reliance on a third party (e.g., accountant) who let you down — but only if you took reasonable steps to monitor them

Excuses HMRC typically rejects:

• "I didn't know I had to file" — ignorance of the law is not an excuse
• "My accountant was too busy"
• "I couldn't afford to pay an accountant"
• "I was abroad" (unless it was an emergency preventing any access)
• "The company isn't trading" — dormant companies must still file a CT600
• "I forgot"

Step-by-Step: How to Appeal

1. Check the deadline You must appeal within 30 days of the penalty notice. You can appeal after 30 days, but you'll need to explain the delay.

2. Decide your route

• Online: Through your HMRC Business Tax Account
• By post: Write to the address on the penalty notice
• By phone: Call the Corporation Tax helpline (0300 200 3410)

3. Gather your evidence Whatever your reasonable excuse, you need supporting evidence. Medical certificates, letters from your accountant, screenshots of HMRC service outages, insurance claims for flood/fire — anything that corroborates your story.

4. Write a clear appeal letter Your appeal should include:

• Your company name and UTR (Unique Taxpayer Reference)
• The penalty reference number
• The period the penalty relates to
• Your reasonable excuse, clearly explained
• Supporting evidence
• The date you filed (or will file) the return

5. Wait for HMRC's decision HMRC typically responds within 30–45 days. They'll either:

• Accept your appeal and cancel the penalty
• Reject your appeal, in which case you can request a review or appeal to the First-tier Tribunal

Appealing to the First-tier Tribunal

If HMRC rejects your appeal and their internal review doesn't change the outcome, you can take your case to the First-tier Tribunal (Tax Chamber). This is an independent body — not part of HMRC.

You must appeal to the Tribunal within 30 days of HMRC's review decision. There's no cost for making a Tribunal appeal, and many directors represent themselves successfully.

For more detail on the appeals process, see our guide on how to appeal a CT600 late filing penalty.

How to Avoid Penalties and Interest

Prevention is obviously better than cure. Here are the practical steps every director should take:

1. Know Your Deadlines

For a company with a 31 March year end:

• Payment deadline: 1 January the following year (9 months + 1 day)
• Filing deadline: 31 March the following year (12 months)

Use our corporation tax deadlines calendar to find your exact dates.

2. File Early

There's no benefit to filing on the last day. File as soon as your accounts are ready. Many companies file months before the deadline — it reduces stress and gives time to fix any issues.

3. Pay on Time (Or Set Up a Payment Plan)

If you can't pay the full amount by the deadline, contact HMRC before the deadline to arrange a Time to Pay (TTP) arrangement. HMRC is far more accommodating when you approach them proactively rather than after the debt has built up.

Interest still accrues during a TTP arrangement, but you'll avoid the stress of enforcement action.

4. Use Software That Files Directly with HMRC

Manual processes increase the risk of missed deadlines. CT600 filing software like Taxpipe calculates your tax, validates your return, and files directly with HMRC — removing the guesswork and delay.

Don't risk penalties. File your CT600 online with Taxpipe — from £59. Direct HMRC submission, automatic calculations, and deadline reminders. Get started →

5. Set Up Calendar Reminders

It sounds simple, but a calendar reminder 60 days before each deadline gives you enough time to prepare without panic. Set two: one for the payment deadline and one for the filing deadline.

HMRC Enquiries and Compliance Checks

Beyond standard penalties, HMRC can open a compliance check (enquiry) into your corporation tax return. This isn't a penalty itself, but it can lead to:

• Additional tax being assessed
• Penalties for inaccuracies (as per the table above)
• Interest on any additional tax from the original due date

What Triggers an Enquiry?

HMRC uses a risk-based system called Connect that cross-references data from multiple sources:

• Your CT600 return data
• Companies House filings
• Bank and building society interest reports
• VAT returns
• PAYE/RTI data
• Third-party data (property transactions, overseas transactions)
• Industry benchmarks

Common triggers include:

• Unusually high expenses relative to turnover
• Significant year-on-year changes in profitability
• Discrepancies between your CT600 and Companies House accounts
• Random selection (about 10% of enquiries are random)

How to Respond

If you receive an enquiry notice, don't panic. You can read more in our guide to HMRC enquiries into your CT600. The key principles are:

1. Respond within the deadline given
2. Provide only what's asked for — don't volunteer extra information
3. Keep records organised and accessible
4. Consider professional help for complex enquiries

Quarterly Instalment Payments: Large Companies

If your company's annual profits exceed £1.5 million (or a lower threshold if you have associated companies), you must pay corporation tax in quarterly instalments rather than in one lump sum.

Missing an instalment payment triggers interest charges from the date the instalment was due. The instalments are due in months 7, 10, 13, and 16 of the accounting period (yes, some fall after the period ends).

For detailed guidance, see our quarterly instalment payments guide.

Special Situations

Company Being Dissolved or Struck Off

If your company is being dissolved, you still need to file a final CT600 and pay any corporation tax due. Penalties can be issued even after dissolution — and HMRC can restore a company to the register specifically to pursue unpaid tax and penalties.

Dormant Companies

Dormant companies that have notified HMRC may be exempt from filing CT600 returns. But if HMRC hasn't confirmed dormancy, you must still file. A nil return takes minutes — there's no excuse for incurring penalties on a dormant company.

Company Bought Off the Shelf

If you bought a shelf company, be aware that its accounting period may have started before you acquired it. Check the dates carefully to avoid a penalty surprise.

Frequently Asked Questions

How much is the penalty for paying corporation tax late?

There isn't a flat penalty for late payment — instead, HMRC charges late payment interest at the Bank of England base rate plus 2.5% (currently around 7.25% per annum). Interest accrues daily from the day after the payment deadline until you pay. For a £10,000 tax bill paid 6 months late, you'd owe approximately £362 in interest.

Can I appeal a corporation tax penalty if I changed accountant?

Yes, but simply changing accountant isn't a reasonable excuse on its own. You'd need to show that the changeover caused an unexpected delay despite taking reasonable steps. For example, if your previous accountant refused to hand over records, that could support your appeal — bring evidence like correspondence showing your attempts to obtain the records.

Does HMRC charge penalties on estimated tax?

If you haven't filed your CT600, HMRC will issue a determination — their own estimate of your tax. This determination has the same legal standing as a filed return, and interest accrues on the estimated amount. The only way to displace a determination is to file your actual CT600 return.

What happens if my company can't afford to pay corporation tax?

Contact HMRC's Payment Support Service (0300 200 3835) before the payment deadline to discuss a Time to Pay arrangement. HMRC will typically agree to monthly instalments over 6–12 months. Interest still accrues during the arrangement, but you'll avoid enforcement action like county court judgments or winding-up petitions.

Are corporation tax penalties tax-deductible?

No. HMRC penalties and interest charges are not allowable deductions for corporation tax purposes. They're paid from post-tax profits, making them doubly expensive — you're paying the penalty from money that's already been taxed.

Summary

Corporation tax penalties and interest charges can escalate quickly, but they're entirely avoidable with proper planning. File early, pay on time, keep good records, and if you do receive a penalty, don't automatically pay it — check whether you have grounds for an appeal.

Take the stress out of corporation tax. Taxpipe helps UK limited companies file their CT600 returns accurately and on time — from just £59. Automatic calculations, built-in validation, and direct HMRC submission. Start your CT600 now →

Related Reading

• Corporation Tax Interest: Late Payment Rates, Repayment Interest & How to Avoid Charges
• How to Appeal a CT600 Late Filing Penalty from HMRC
• How to Correct a CT600 Mistake: Amending Your Corporation Tax Return