What Happens If I File Company Tax Late? (UK Penalties Explained)

Missing your corporation tax filing deadline can be expensive. HMRC and Companies House both impose penalties — and they're separate, so you could face charges from both bodies.

Here's exactly what happens, what it costs, and what you can do about it.

The Two Deadlines You Need to Know

Your UK limited company has two key filing deadlines after each accounting period ends:

Example: If your accounting period ends 31 March 2026:

• Accounts due at Companies House: 31 December 2026
• Corporation tax payment due: 1 January 2027
• CT600 return due at HMRC: 31 March 2027

HMRC Penalties for Late CT600 Filing

HMRC imposes automatic penalties for late CT600 returns. No warnings — the penalty is applied immediately once the deadline passes.

Important Notes:

• The £100 penalties apply even if you owe no tax (e.g., dormant or loss-making companies)
• If you've been late with 3 consecutive returns, the flat penalties increase to £500 each
• These penalties are on top of any interest charged on late tax payments
• The 6-month and 12-month penalties are based on HMRC's estimate of your tax liability — this may be higher than the actual amount

HMRC Interest on Late Payment

If you pay your corporation tax late (after the 9 months + 1 day deadline), HMRC charges interest from the day after the deadline until the date you pay. The current late payment interest rate is regularly updated — check HMRC's website for the latest rate.

Interest is charged automatically and compounds daily. Even a few weeks' delay can add up.

Companies House Penalties for Late Accounts

Companies House penalties for late accounts are separate from HMRC penalties and are not negotiable:

Key Points:

• These penalties double if you were late the previous year
• Penalties are imposed on the company, not the director personally (but directors are responsible for ensuring compliance)
• Unlike HMRC, Companies House does not reduce penalties for companies that owe no tax — the penalty is for late filing regardless

Total Cost of Being Late: An Example

Scenario: Your accounts period ended 31 March 2026. You file everything 4 months late.

For a company that might only owe a few hundred pounds in tax, these penalties can exceed the actual tax liability.

What If You've Already Missed the Deadline?

File as Soon as Possible

The penalties increase over time, so every day counts. File immediately to prevent further penalties from accumulating.

You Can Appeal HMRC Penalties

You may be able to appeal if you have a "reasonable excuse" such as:

• Serious illness or bereavement
• HMRC's online service was unavailable
• Fire, flood, or theft affecting your records
• A partner or close relative died shortly before the deadline

HMRC does not consider the following as reasonable excuses:

• You didn't know about the deadline
• You relied on someone else to file
• You didn't receive a reminder
• You didn't owe any tax

Companies House Appeals

Companies House rarely accepts appeals. Their position is that directors should know their filing deadlines. However, you can apply for an extension before the deadline if you know you'll be late.

How to Avoid Late Filing

1. Know your deadlines — mark them in your calendar as soon as your accounting period ends
2. Don't wait until the last minute — start preparing your accounts at least 2-3 months before the deadline
3. Use software — tools like SimpleCompanyTax can prepare your CT600 and accounts same-day
4. Set reminders — at 6 months, 3 months, and 1 month before each deadline
5. File even if you can't pay — filing your return on time avoids the filing penalties, even if you need more time to pay the tax

Dormant Companies Are Not Exempt

A common misconception: even if your company is dormant and owes no tax, you still need to file:

• Dormant accounts at Companies House
• A CT600 return at HMRC (confirming the company is dormant)

Missing these deadlines still incurs the same penalties. Many directors of dormant companies get caught out by this.

Summary

Late filing is expensive and entirely avoidable. The key deadlines are 9 months (Companies House accounts), 9 months + 1 day (tax payment), and 12 months (CT600 return) after your accounting period ends. Penalties start at £100 from HMRC and £150 from Companies House and escalate rapidly.

The cheapest approach: file on time. The fastest approach: use software that can prepare everything in a single session.