Corporation Tax returns explained: CT600 filing requirements for UK companies
A company’s CT600 is closely linked to its accounts, tax computations, iXBRL tagging and payment timetable.
A Corporation Tax return normally includes the CT600, statutory accounts and tax computations. GOV.UK explains that companies must file a Company Tax Return when HMRC sends a notice to deliver one. HMRC Company Tax Return guidance.
Corporation Tax return deadlines
For private limited companies, GOV.UK states that annual accounts are normally due at Companies House 9 months after the financial year end, Corporation Tax payment is due 9 months and 1 day after the accounting period ends, and the Company Tax Return is due 12 months after the accounting period ends. GOV.UK accounts and tax return deadlines.
Software filing from April 2026
HMRC states that the joint online service to file accounts and Company Tax Returns closed on 31 March 2026, and from 1 April 2026 companies should use commercial software to file annual accounts and Company Tax Returns with HMRC. HMRC service closure guidance.
Common CT600 issues
- Reconciling accounting profit to taxable profit.
- Capital allowances and fixed asset additions.
- Related party balances and loan relationships.
- Disallowable expenses and entertaining.
- iXBRL tagging errors.
Frequently asked questions
Clear answers to common questions on this topic.
What is a CT600?
A CT600 is the Company Tax Return form submitted to HMRC with supporting accounts and computations.
When is Corporation Tax due?
GOV.UK states that Corporation Tax is normally payable 9 months and 1 day after the accounting period ends.
When is the Company Tax Return due?
GOV.UK states that the Company Tax Return is normally due 12 months after the accounting period ends.
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