HMRC CT600 filing is the Corporation Tax return workflow. UK companies should prepare the CT600, tax computations and iXBRL-tagged accounts where required, then validate the filing pack and retain HMRC submission evidence.
This guide is source-linked to official HMRC, Companies House and FRC material where available. Check current official guidance before treating the filing route, deadline or taxonomy choice as final.
What the HMRC pack covers
The HMRC Company Tax Return pack centres on the CT600, Corporation Tax calculation, tax computations and supporting accounts. iXBRL tagging is part of making the relevant accounts or computations digitally readable where required by the filing workflow.
- Prepare CT600 from the final tax position.
- Align accounts and computations before tagging.
- Validate the iXBRL file before submission.
Why Companies House is still separate
Companies House filing may use the same statutory accounts, but it is not the HMRC tax return. Treat the Companies House confirmation as accounts filing evidence and the HMRC confirmation as Company Tax Return evidence.
- Do not rely on a Companies House receipt as HMRC filing evidence.
- Do not rely on an HMRC receipt as Companies House accounts evidence.
- Record both when both obligations apply.
Review controls
The final review should reconcile accounts, CT600 figures, tax computations, iXBRL tags and validation messages before the filing is released.
- Check profit, tax charge and key disclosures.
- Review validation warnings, not only blocking errors.
- Save final submission files and acknowledgements.
Common risks
Common risks include treating HMRC and Companies House as one combined filing, using an old taxonomy assumption, copying prior-year tags without review, ignoring validation warnings, missing separate deadlines and losing evidence of approval.
- Do not rely only on prior-year files.
- Do not treat validation as a substitute for accounting or tax review.
- Escalate unusual balances, late filings or regulator-specific issues early.
Evidence to retain
The filing record should show the source accounts used, the HMRC or Companies House route decision, mapping or tagging review, validation results, corrections, approvals and final filing confirmation.
- Save signed or approved accounts and version details.
- Save validation and correction evidence for iXBRL files.
- Save HMRC, Companies House, upload or adviser handoff confirmation.
Before you rely on this route
- CT600 reviewed.
- Tax computations reviewed.
- Accounts version locked.
- iXBRL validation evidence saved.
- HMRC acknowledgement retained.
Official sources
Use these official references as the current regulatory baseline before making filing decisions.
FAQs
What is the short answer?
HMRC CT600 filing is the Corporation Tax return workflow. UK companies should prepare the CT600, tax computations and iXBRL-tagged accounts where required, then validate the filing pack and retain HMRC submission evidence.
Are HMRC and Companies House filings the same?
No. Companies House accounts filing and HMRC Company Tax Return filing are separate UK obligations, even where the same statutory accounts support both workflows.
Can prior-year iXBRL files be reused?
Prior-year files can be a reference, but the current company facts, accounts, taxonomy, validation rules and official filing route should be checked again.
When should professional review be used?
Use professional review when the route is unclear, the filing is late, source documents changed, CT600 or tax computations changed, or the entity has unusual disclosures.
This article is general UK iXBRL filing information, not legal, tax, accounting or regulatory advice. Check current HMRC, Companies House and FRC guidance, and seek professional advice before making filing decisions.