If your accounts cover a period of more than 12 months, you'll need to complete the CT600 for two periods, as follows:
- Prepare the accounts for the full period and generate an XBRL version or PDF-with explanation (if required).
- Apportion the profit/loss into a 12-month period and the remaining days – using days meets the HMRC guidelines.
- Create the first (12-month) period return in TaxCalc (see instructions below).
- Create the second (short) period return in TaxCalc (see instructions below).
- Contact Support to resolve the filing restriction message.
How to create the first period return
- Open TaxCalc 2026.
- Click on Create a New CT600 Corporation.
- Click on SimpleStep.
- Go to CT600 Full/Short or Core > Return Period.
- Enter the 12-month period.
- Go to Accounts and Computations.
- Under I am attaching Accounts..., tick Relating to a different period.
- Enter the apportioned figures into Computations.
- Complete the rest of the return.
- Attach the XBRL accounts (for the full period).
How to create the second period return
- Open TaxCalc 2026.
- Click on Import Returns from TaxCalc 2025.
- Browse and select the 12-month period you just created.
- Open the return.
- Click on Simple Step.
- Go to CT600 Full/Short or Core> Return Period.
- Enter the remaining period.
- Go to Accounts and Computations.
- Under I am attaching Accounts..., untick both Relating to this period and Relating to a different period.
- Select Submitted with accompanying return from the drop-down menu – you don't need to send the accounts again.
- Enter the apportioned figures into Computations.
- Complete the rest of the return.
Cookie Settings