Beta This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Company Taxation Manual

Corporation Tax self-assessment (CTSA): Assessments: General

CTSA accounting periods

CTSA is a major change to CT assessing procedures.

Normally, rather than the Revenue, the company makes its assessment as part of the making of its return. The Revenue has specific powers to amend returns and an SA and retains a power to make discovery assessments.

The SA contained in a company tax return creates a legal charge to tax. Subject to the right to make a discovery assessment (see CTM95030 onwards) or discovery determination (see CTM95500 onwards) the return is final once made, unless within the relevant time limits.

  • the company amends it (see CTM93300 and the On-line Company Tax Manual (COM) in the “Returns” business area),
  • the Inspector decides to enquire into it,
  • the conclusions stated at the end of an enquiry into a return for a different period require a consequential amendment to it (FA98/SCH18/PARA34 (1)(b)).

There is a new statutory framework for enquiries into company tax returns. The rules mirror those for IT SA and apply for accounting periods ending on or after 1 July 1999.

See the Enquiry Manual for guidance on opening and conducting enquiries.

CTPF accounting periods

CTPF is not a full “SA” system.


  • companies have to pay tax by the due date, whether or not an assessment has been made to avoid interest charges, and
  • the tax liability shown in a return is collectible as if it were tax due and payable under an assessment,

the system is one of “Revenue Assessment”. You have to make an assessment in accordance with the return, if you are satisfied with it, and can make an estimated assessment if:

  • you are not satisfied with the return, or
  • the company does not make a return.

CTPF did not alter the legislation on assessments, appeals and postponement applications. One of the main aims of CTPF though, was to reduce the need to make estimated assessments.