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Corporation TaxUpdated 2026-10-19

When is Corporation Tax due?

Quick Answer

Corporation Tax is due 9 months and 1 day after your company's accounting period ends. Your CT600 return must be filed within 12 months of the accounting period end.

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Detailed Explanation

Corporation Tax has two key deadlines:

Payment deadline

9 months and 1 day after your accounting period ends - Example: If your year ends 31 March 2025, payment is due by 1 January 2026

Filing deadline (CT600)

12 months after your accounting period ends - Example: If your year ends 31 March 2025, your return is due by 31 March 2026

Large companies

If your taxable profits exceed £1.5 million, you must pay in quarterly instalments starting in month 7 of your accounting period.

Late payment interest

HMRC charges interest from the day after the payment deadline. Currently around 7.75%.

Late filing penalties

- 1 day late: £200 - 3 months late: Another £200 - 6 months late: 10% of unpaid tax - 12 months late: Another 10% of unpaid tax

Source: HMRC Corporation Tax Deadlines

Real-World Examples

Missed Deadline Penalty

Your company's accounting period ends on 30 June 2025. The Corporation Tax payment is due on 1 April 2026, but you forget and pay on 5 April 2026. HMRC will charge penalties and interest on the late payment.

Planning for Future Tax

You anticipate a substantial profit in your accounting period ending 31 December 2024. To avoid a large tax bill on 1 October 2025 (9 months and 1 day after year end), you start setting aside funds each month, treating Corporation Tax as a regular expense.

Correcting Errors Before Deadline

While preparing your CT600 for the year ending 31 March 2025, you discover an error in your initial calculation. You still have time to correct the error and ensure accurate filing and payment before the respective deadlines of 31 March 2026 (filing) and 1 January 2026 (payment).

Common Mistakes to Avoid

  • Forgetting to factor in bank holidays or weekends when calculating the payment deadline, as this doesn't extend the due date.
  • Assuming the accounting period always aligns with the calendar year; it can be any 12-month period you choose initially.
  • Failing to update your accounting software or spreadsheet with the correct Corporation Tax rate for the relevant financial year.
  • Not keeping adequate records to support the figures declared in your CT600 return, leading to potential issues during an HMRC enquiry.

What happens if I pay my Corporation Tax early?

Paying early is perfectly acceptable! HMRC will simply credit your account. Just ensure the payment is correctly allocated to the right accounting period.

If my company is dormant, do I still need to file a CT600?

Yes, even dormant companies must file a CT600 unless they qualify for an exemption. You'll declare no trading activity for the relevant period.

Can I change my company's accounting period end?

Yes, you can change your accounting period end, but there are rules. You must notify Companies House and HMRC, and the period cannot generally exceed 18 months from the previous period end. Changing it too frequently may raise scrutiny from HMRC.

Where do I find my company's Corporation Tax Unique Taxpayer Reference (UTR)?

Your UTR is a 10-digit number and can be found on previous correspondence from HMRC regarding Corporation Tax, such as the 'Notice to deliver a Company Tax Return' (CT410) form. You'll need this to pay your Corporation Tax.

Practical Tips

  • Set up a reminder in your calendar well in advance of both the payment and filing deadlines to avoid late penalties.
  • Use accounting software that automatically calculates your Corporation Tax liability based on your financial data.
  • Reconcile your bank statements and other financial records regularly to ensure accurate financial reporting and tax calculations.
  • If you're unsure about any aspect of Corporation Tax, seek professional advice from a qualified accountant or tax advisor.

Related Questions

What is the Corporation Tax rate in 2025?

The main Corporation Tax rate is 25% for profits over £250,000. Small profits rate is 19% for profits under £50,000. Marginal relief applies between £50,000 and £250,000.

How do I file a CT600 Corporation Tax return?

File your CT600 online through HMRC's Company Tax Return service or commercial software. You need your company UTR, accounts, and tax computations. The deadline is 12 months after your accounting period ends.

What expenses reduce Corporation Tax?

Most genuine business expenses reduce your Corporation Tax bill, including salaries, rent, utilities, professional fees, travel, equipment, and pension contributions. The expense must be 'wholly and exclusively' for business purposes.

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