Start with completed accounts
The return normally draws on the statutory accounts and a Corporation Tax computation. Unreconciled bookkeeping or unresolved balance-sheet items can therefore hold up the CT600.
Prepare the tax information
Bring together the transactions and claims that may differ between accounting and tax treatment.
- Fixed assets and capital allowances
- Director loans and related-party balances
- Interest and financing costs
- Losses and reliefs
- Donations, grants and unusual income
- Tax already paid and the correct payment reference
Confirm the return period
Check the accounting period shown by HMRC. A long first period or a changed year end can mean that more than one return is required.
Use compatible filing software
HMRC requires online filing in the normal course. From 1 April 2026, companies should use commercial software for annual accounts and Company Tax Returns, subject to the limited paper-filing exceptions in HMRC guidance.
Official guidance
Reviewed against the following official sources. Always check the current guidance for your company and accounting period.
- Completing your Company Tax ReturnHM Revenue & Customs / GOV.UK
- Filing company accounts and tax returns after the joint service closureHM Revenue & Customs / GOV.UK
- Company Tax Return obligationsHM Revenue & Customs / GOV.UK
This guide is general information, not tax, legal or financial advice for your circumstances. Filing requirements and deadlines should be checked for the relevant person, company and period.