# Corporation Tax Deadlines Calculator

> Enter your company's accounting period to see when Corporation Tax is due, when the CT600 must be filed and when accounts are due at Companies House.

Enter your accounting period to see the payment and filing dates, including the two returns needed for a period longer than 12 months.

Use the calculator: https://www.taxoptimiser.co.uk/calculators/corporation-tax-deadlines

Example: For the year from 1 April 2025 to 31 March 2026, Corporation Tax is due by 1 January 2027, the Company Tax Return by 31 March 2027 and the accounts at Companies House by 31 December 2026.

## When Corporation Tax is due

Corporation Tax is due nine months and one day after the end of the accounting period, so before the return itself is due. Companies with taxable profits above £1.5 million pay in instalments instead.

## When the CT600 is due

The Company Tax Return is due 12 months after the end of the period the accounts cover.

## Accounts longer than 12 months

A corporation tax accounting period cannot be longer than 12 months. If your accounts cover a longer period, such as a first period, you file two returns: one for the first 12 months and one for the rest. Each has its own payment date, but both returns are due 12 months after the end of the accounts.

## When accounts are due at Companies House

A private company must file its accounts at Companies House within nine months of the end of its financial year. First accounts that cover more than 12 months are due 21 months after the date of incorporation, or three months after the end of the financial year if that is later. Both dates are earlier than the Company Tax Return deadline, so the accounts are normally finished first.

## Frequently asked questions

### When are company accounts due at Companies House?

Nine months after the end of the financial year for a private company. First accounts covering more than 12 months are due 21 months after incorporation, or three months after the end of the financial year if later.

### When is Corporation Tax due?

Nine months and one day after the end of the accounting period. Companies with taxable profits above £1.5 million pay in instalments instead.

### When must the CT600 be filed?

The Company Tax Return is due 12 months after the end of the period the accounts cover, so the tax is due before the return.

### What if my accounts cover more than 12 months?

You file two Company Tax Returns: one for the first 12 months and one for the rest. Each has its own payment date, but both returns are due 12 months after the end of the accounts.

## Related calculators

- [Late Filing Penalty Calculator](https://www.taxoptimiser.co.uk/calculators/late-filing-penalties.md): Companies House and HMRC penalties for late accounts and a late CT600.
- [Corporation Tax Calculator](https://www.taxoptimiser.co.uk/calculators/corporation-tax.md): Estimate Corporation Tax for a UK limited company with marginal relief.
- [Company Accounts Type Checker](https://www.taxoptimiser.co.uk/calculators/accounts-type-checker.md): Micro-entity, small or dormant accounts, and whether the free Companies House service is still open.
- [Director's Loan (S455) Calculator](https://www.taxoptimiser.co.uk/calculators/directors-loan-s455.md): Section 455 tax on an overdrawn director's loan, with due and refund dates.

## Sources

- [Pay your Corporation Tax bill](https://www.gov.uk/pay-corporation-tax) (GOV.UK)
- [Company Tax Returns](https://www.gov.uk/company-tax-returns) (GOV.UK)
- [Accounts and tax returns for private limited companies](https://www.gov.uk/annual-accounts) (GOV.UK)
- [Your limited company's first accounts and Company Tax Return](https://www.gov.uk/first-company-accounts-and-return) (GOV.UK)

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Last updated 11 October 2026. Guidance only: a general estimate, not tax advice. Published by Tax Optimiser, UK tax filing software (https://www.taxoptimiser.co.uk).