Corporation tax self assessment (CTSA) requirements

Produced by Tolley

The following Corporation Tax guidance note Produced by Tolley provides comprehensive and up to date tax information covering:

  • Corporation tax self assessment (CTSA) requirements
  • Corporation tax returns
  • Duty to notify chargeability
  • Notice to file a corporation tax return (CT603)
  • Due date for filing a corporation tax return
  • Long periods of account
  • Mandatory online filing for corporation tax returns
  • Amendments to corporation tax returns
  • Register of people with significant control (PSC)

Corporation tax self assessment (CTSA) requirements

The corporation tax self assessment (CTSA) regime applies to companies and deals with the administration and payment of corporation tax. The key administrative points are set out below.

For details on the payment of corporation tax, see the How to pay corporation tax guidance note.

For information on UK tax filing requirements as they apply to overseas companies, see the UK filing requirements guidance note.

Corporation tax returns

Corporation tax returns (CT600) must be submitted to HMRC for the accounting period in question and must include information, accounts statements and reports relevant to the tax liability of the company. It must also contain a declaration that the return is correct and complete to the best of the knowledge of the person submitting it (an authorised signatory of the company).

In practice, the CT600 is accompanied by:

  1. a set of signed financial statements for the accounting period, which includes the signed directors’ report

  2. detailed analysis necessary to show that the return is correct and complete, which is usually the corporation tax computation


The company must ensure that:

  1. tax on loans to participators is included in the total amount of tax payable

  2. all other necessary adjustments are made in arriving at TTP, such as transfer pricing adjustments for example

Duty to notify chargeability

Companies have an obligation to notify HMRC when their first chargeable accounting period begins or when they come back within the charge to corporation tax after a period of dormancy. Certain prescribed information must be provided.

The company must give written notice within 3 months of the start of the accounting period.

The notice must state when the chargeable accounting period began.

The rules do not apply to unincorporated associations or partnerships.

The detailed information to be given in the notice is as follows:

  1. the company’s name and registration number

  2. the address of the company’s registered office

  3. the address of the company’s principal place of business

  4. the nature of the business being carried on by the company

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