What are HMRC’s Corporation Tax Penalties?

The letter from HMRC rarely announces itself as urgent. The tone is flat: “Our records show…”, “you may be liable…”, a reference number, a figure. Directors who have not seen one before tend to file it, pay it, or query it in roughly equal proportions. Each of those responses has a different cost six months later.

Corporation Tax penalties compound in a specific way. The fixed penalty for a missed filing is not the story. The behaviour-based penalty for the underlying inaccuracy is the story, and its calculation, which moves with cooperation, disclosure, and whether the error was “careless” or “deliberate”, can take a five-figure bill into six figures without the director noticing.

Below we cover the specific Corporation Tax penalty categories, the statutory basis for each, how behaviour tiers change the amount you owe, and the practical options for reducing or appealing a penalty before it becomes enforced debt.

Why Corporation Tax Penalties Matter More Than Directors Think

Corporation Tax penalties live in two separate regimes that combine on any given case.

• Fixed late-filing penalties under Schedule 18 of the Finance Act 1998: £200 as soon as the return is late, rising to £400 in total once it is more than three months late (for returns due on or after 1 April 2026; it was £100 and £200 before); 10% of the tax unpaid if the return is still missing 18 months after the period ends; 20% in total if it is still missing after two years.
• Behaviour-based inaccuracy penalties under Schedule 24 of the Finance Act 2007: up to 30% of the potential lost revenue for careless errors, up to 70% for deliberate, and up to 100% for deliberate and concealed. These apply to the inaccuracy itself, not to late filing.
• Interest on late payment of Corporation Tax at HMRC’s published rate (currently 7.75% for late payment; rates track Bank of England base rate + 4%).

The combined effect is the bit most directors miss. If your company filed late, paid late, and had a small understatement, you can face a fixed filing penalty, a percentage penalty on unpaid tax, interest on the tax, and a separate behaviour-based penalty on the understatement. Four separate charges stacked on what you originally treated as “a bit of admin we fell behind on”.

If you ignore any of these, the escalation path leads to HMRC enforcement action, enforcement agents taking control of the company’s goods, a statutory demand, and eventually a winding-up petition.

The penalties are not collected through a separate process. They are simply tax your company owes.

The Main Types of Corporation Tax Penalties

The penalty architecture under UK tax law splits into four categories. Each has its own statutory basis, its own trigger, and its own route to mitigation.

Late filing penalties (CT600)

The CT600 corporation tax return is normally due 12 months after the end of the accounting period (it can be later, for example where the period of account is longer than 12 months or HMRC’s notice to file arrived late). Miss that deadline and:

• A £200 fixed penalty applies immediately (£100 for returns due before 1 April 2026).
• A further £200 after three months, making £400 in total (£200 for returns due before 1 April 2026).
• If the return is still not filed 18 months after the end of the accounting period (six months after the usual deadline), HMRC adds a penalty of 10% of the tax unpaid at that point (the “tax-geared” penalty).
• At twelve months, another 10% tax-geared penalty on the unpaid amount.
• If the company was also late with each of its two previous returns, the fixed penalties rise to £1,000 and £2,000 (£500 and £1,000 for returns due before 1 April 2026).

Late payment penalties on Corporation Tax

For most companies, Corporation Tax is due nine months and one day after the accounting period ends, three months before the filing deadline. Large companies pay earlier, in quarterly instalments. Late payment attracts interest at the current HMRC rate and, where the return itself is filed more than six months late, the tax-geared penalties described above.

Inaccuracy penalties under Schedule 24

Where the return contains an error that leads to an understatement of tax, HMRC can impose an inaccuracy penalty scaled to the behaviour behind the error.

• Careless: up to 30% of the potential lost revenue; HMRC can reduce this to as low as 0% for an unprompted disclosure, or 15% for a prompted one.
• Deliberate (not concealed): up to 70% of PLR; reducible to as low as 20% for an unprompted disclosure, or 35% for a prompted one.
• Deliberate and concealed: up to 100% of PLR; reducible to as low as 30% for an unprompted disclosure, or 50% for a prompted one.

“Reasonable care” is the safe harbour. Where your company genuinely tried to get it right and the error was innocent, no penalty arises under Schedule 24, as long as you tell HMRC promptly if you later find the error.

Failure to notify penalties

A new company must tell HMRC within three months that its first accounting period has started, and missing that can bring a separate penalty.

A company that has not received a notice to file a return, and does not tell HMRC it is chargeable to Corporation Tax within 12 months of the end of the accounting period, faces a failure to notify penalty under Schedule 41 of the Finance Act 2008. Its behaviour tiers and disclosure reductions work much like Schedule 24.

How Behaviour Tiers Determine Corporation Tax Penalty Amounts

The word that changes everything in a Schedule 24 enquiry is “careless” versus “deliberate”. The gap between the two is measured in tens of thousands.

HMRC’s test for each:

• Reasonable care, the taxpayer took appropriate steps to get the position right. No penalty, as long as any error found later is reported to HMRC promptly.
• Careless, the taxpayer failed to take reasonable care: what a prudent person in the company’s position would have done. The company’s abilities and circumstances are taken into account, but simply not knowing the rules is rarely enough.
• Deliberate, the taxpayer knew the return was wrong and submitted it anyway.
• Deliberate and concealed, deliberate error plus active steps to hide it (false records, concealment of transactions).

The reductions within each tier are driven by three factors: telling (quality of your disclosure), helping (your cooperation with the enquiry), and giving (providing access to records). HMRC reduces the penalty percentage within the statutory range based on scores for each. Our experience is that proactive cooperation moves the needle materially.

Getting your behaviour category right is typically the single biggest commercial point in any enquiry. The difference between “careless” and “deliberate” on a £50,000 error is the difference between a £15,000 penalty and a £35,000 one, before the reductions.

Failure to Notify and Other Corporation Tax Oversights

The category of penalty that catches first-time directors out most often is failure to notify. Your new company must tell HMRC within three months that its first accounting period has started. Missing that is not rare. Most accountants pick it up when the first set of accounts comes round, but the window will already have passed.

Other recurring oversights that attract penalties:

• Close company loans to participators, a refundable section 455 tax charge on director’s loan balances still outstanding nine months after the period end: 35.75% for loans made on or after 6 April 2026 (33.75% for loans made from 6 April 2022 to 5 April 2026). Often missed.
• Group relief errors, incorrect surrender of losses between group companies.
• Transfer pricing adjustments where related-party transactions were not conducted at arm’s length.
• R&D tax credit claims disallowed on HMRC review, with a behaviour-based penalty where the claim was not reasonable.

Each of these has its own complexity, but all run through the same Schedule 24 behaviour framework once an inaccuracy is identified.

Reducing or Appealing Corporation Tax Penalties

Three routes to reduce a penalty, applicable in most cases:

Unprompted disclosure

Disclosure made before you have any reason to think HMRC is about to discover the error. This produces the biggest reduction in penalty bands; careless errors can go to 0%. If your accountant spots an error in last year’s return, filing an amendment voluntarily before any HMRC contact is often cheaper by 20–30 percentage points of penalty.

Prompted disclosure with full cooperation

Disclosure once HMRC has opened an enquiry but before it has found the error on its own. Your reduction is smaller than unprompted but still material, often 15–20 percentage points depending on the quality of your cooperation.

Formal appeal

Within 30 days of the penalty notice, your company can appeal to HMRC on grounds including reasonable excuse, incorrect application of the behaviour tier, or incorrect calculation of the potential lost revenue. If HMRC upholds the penalty, you can take the appeal to the First-tier Tribunal (Tax Chamber).

The most common successful appeal ground is “reasonable excuse”: unexpected illness, bereavement, third-party failure (software, accountant), or other events outside your control. The bar is real. Generic business pressure is not a reasonable excuse in itself.

Corporation Tax Penalty Case: How the Numbers Actually Stack

A worked example: a company with a £40,000 Corporation Tax liability that filed nine months late and understated tax by £12,000 through a careless error in R&D treatment. If you are in this position, the penalties stack:

• £200 fixed late filing + £200 at three months = £400
• £4,000 tax-geared penalty (10% of £40,000 at six months late)
• Interest on late payment, roughly £2,300 at current rates across a year
• Careless inaccuracy penalty of 15% (prompted, moderate cooperation) on £12,000 PLR = £1,800

Total penalty and interest: ~£8,500 on top of the original £40,000 tax. Careful pre-emption on your part (unprompted disclosure on the R&D point, earlier filing even without payment) could have reduced that total by roughly half.

These are not edge cases. They are the standard arithmetic of the UK Corporation Tax penalty regime when applied to a company that did not act promptly.

When Corporation Tax Penalties Signal a Wider Problem

Large accumulated HMRC debt, particularly where it sits alongside other creditor pressure, is one of the clearest external indicators of cash-flow insolvency.

Persistent late filing and repeated penalty notices are pattern evidence in any subsequent insolvency review. An Insolvency Practitioner’s conduct report specifically addresses your compliance history, and we see it used against directors who thought HMRC arrears were a company problem rather than a personal one.

Where your company cannot pay the underlying tax and accumulating penalties, HMRC can refuse a standard Time to Pay arrangement.

At that point your next steps move onto the enforcement track: HMRC enforcement, potentially Personal Liability Notices for NIC, and eventually liquidation action.

A licensed insolvency practitioner involved early can often negotiate a better HMRC outcome than you would reach alone, partly because our presence signals that formal process is on the table, and partly because we can model whether a CVA or administration produces a better result for everyone.

Your Next Step on Corporation Tax Penalties

Three practical calls, in order of urgency:

1. Accountant, on penalty calculation and any possible unprompted disclosure on underlying inaccuracies.
2. Tax specialist, if the behaviour category is contested or the inaccuracy is complex.
3. Licensed insolvency practitioner, if the penalties sit alongside broader HMRC arrears and cash flow is tight.

Our licensed IPs and business rescue specialists can assess the position, handle the HMRC conversation, and implement a formal process where one is the right answer. Call us free on 0800 074 6757 for confidential advice.

FAQs on Corporation Tax Penalties