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How should boxes 326, 327 and 328 be completed on a CT600?

This article will explain how and when boxes 326, 327 and 328 should be populated on a CT600 return with regard to the number of associated companies.

Firstly, you should review HMRC's company tax return guide to confirm if entries are required in these boxes. An extract has been provided below for your convenience:

326 Number of associated companies in this period

You must enter the number of companies associated with your company for any part of the accounting period if either the:

  • company’s profits are chargeable at the small profits rate
  • company is entitled to Marginal Relief

The figure should not include your company.

Note: an associated company is counted even if it is an associated company for only part of an accounting period, therefore box 326 should still be used. The exception to this, is if the CT period straddles two financial years and rates or limits differ between those financial years. Only then should boxes 327 and 328 be completed.

For accounting periods ending on or after 1 April 2023, large and very large companies must complete this box with the number of associated companies at the end of the previous accounting period. The figure should not include your company.

Find out more about associated companies by reading the Company Taxation Manual (CTM03500

For more information about large and very large companies, read regulation 3(7) of the Corporation Tax (Instalment Payments) Regulations 1998.

327 and 328 Number of associated companies in the first and second financial years

Make entries in boxes 327 and 328 instead of box 326 if all of the following apply:

  • accounting period straddles 2 financial years
  • upper or lower limit has changed
  • number of associated companies was different in each of the financial years

The figure should not include your company.

To begin data entry in TaxCalc, please browse to the below locations:

SimpleStep Mode - CT600 Core > Corporation tax chargeable

HMRC Forms Mode - CT600 Core > Core > Page 4

Box 326 - Number of associated companies in this period

This box shall be locked if the period straddles 1st April 2023 as boxes 327 and 328 should be used OR if the accounting period end is prior to 01/04/2023 as these boxes are only to be used when the rate of corporation tax has changed.

Box 327 - Number of associated companies in the first financial year

This box should be used for any periods that straddle 1st April 2023

Box 328 - Number of associated companies in the second financial year 

This box should  be used for any periods that straddle 1st April 2023

If you are receiving an error in regards to boxes 327 and 328 and there are no associated companies, please enter a 0 into both boxes. As per the screenshot below even though both boxes are red, you are still able to make an entry.

Once a 0 has been entered in both boxes, the error you are receiving will be cleared.