Status: preview. You can prepare the return and preview its boxes here. It runs on our simulator and HMRC's test service only, so nothing you send reaches HMRC.
Which company?
Company Tax Return
Company (). Change company.
Review
Check your answers. These are the figures HMRC will receive. Nothing has been sent to HMRC yet.
The Company Tax Return guide explains each box. The form itself is the CT600 (2026) Version 3.
Your answers
CT600 boxes
| Box | Meaning | Value (amounts in £) | Change |
|---|
Computations
| Line | £ | Change |
|---|
Send to HMRC
How we protect your filing data is in the security statement.
6 to 8 characters, from Companies House. It is sent once with the accounts and never stored.
Companies House prints this in the revised accounts, under the statement that they replace the accounts it holds.
Sign in with the Government Gateway user ID and password for the company's Corporation Tax enrolment. They are sent once with this return and never stored.
Return result
Companies House
HMRC
Amend this filing
Amend the return when a tax answer was wrong. Amend the accounts and the return when a figure in the accounts was wrong: Companies House gets revised accounts, then HMRC gets an amended return. Your receipts show the amendments under this filing.
The loss claimed in return 2 changes return 1. Amend return 1 so HMRC holds the figures you sent with return 2.
Where to get help
- A problem with the live HMRC service, or with the Government Gateway: the HMRC Online Services Helpdesk.
- A problem with this software: DIY Accounting at support@diyaccounting.co.uk, or the Help page.