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Amend the first CT600 and file the second as new

Last updated: 12 October 2026

Short version. Use these steps when the first CT600 needs correcting, the second has not been filed, and your full accounts period is over 12 and no more than 18 months. Read which accounts to attach and how HMRC handles the returns first.

Go to the steps and entry details

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Enter and review both returns

  1. Choose Amend filing made elsewhere for your company. Use this route even if the first CT600 was filed through this service.
  2. In Company & period, check the company details and choose the full accounts period from the Companies House list, or choose Custom dates. Choose HMRC CT600 under What are you filing?
  3. Under Filing purpose, select Amend the first CT600 and file the second as new. If the full tax span differs from the accounts period, tick My HMRC Corporation Tax period is different from my statutory accounts period and enter both tax dates. Set First CT600 ends to the end of the first CT600 HMRC shows. Check both displayed periods. Follow the date-matching steps.
  4. Enter your full-period figures and any requested allocations between the two CT600 periods.
  5. On review, read HMRC returns to file. The first is an amended return and the second is a new return. Review both CT600s, their computations and the full statutory accounts.
  6. Enter your Reason for amendment, select HMRC and complete the existing approval and filing steps.
  7. Check the HMRC result for each period separately. A rejection applies to that return. Selective automatic retry is not included.

Changing the filing destinations

Selecting Companies House clears this filing purpose. If you also file to HMRC afterwards, both CT600s are amendments. Review the changed package before submitting.