The Corporation Tax calendar runs backwards from what most people expect: you pay before you file.

The two deadlines

For a company with an accounting period ending 31 December 2026:

• Payment: 1 October 2027 (9 months and 1 day after the period end)
• Return: 31 December 2027 (12 months after the period end)

New companies, watch out: you can have two accounting periods in your first year, which means two sets of deadlines. HMRC’s online account shows yours. Very large companies pay in quarterly instalments instead, but that does not touch a typical small business.

Late filing penalties

• 1 day late: £200
• 3 months late: another £200
• 6 months late: HMRC estimates your bill and adds 10% of the unpaid tax
• 12 months late: another 10%

File late three times running and the £200 penalties become £1,000 each. At 6 months HMRC issues a “tax determination”, its own estimate of what you owe, and you cannot appeal it: the only way out is to file the real return.

Late payment

Interest runs from the day after the payment deadline until you pay. There is no separate fixed penalty for late payment of the tax itself; the interest is the charge, and it compounds quietly.

The Companies House date, for completeness

Your company accounts go to Companies House separately, normally 9 months after the financial year end for a private company. Different organisation, different deadline, different penalties. It catches people who assume filing with HMRC covers everything.

Sources

All pages checked 20 October 2026.

• Company Tax Returns: https://www.gov.uk/company-tax-returns
• Pay your Corporation Tax bill: https://www.gov.uk/pay-corporation-tax
• Penalties for late filing: https://www.gov.uk/company-tax-returns/penalties-for-late-filing
• File your company’s annual accounts with Companies House: https://www.gov.uk/file-your-company-annual-accounts

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