12 months after accounting period end
Corporation Tax Return (CT600) Deadline
CT600 return filing deadline - 12 months after your accounting period ends
When it's due
12 months after accounting period end
Who This Applies To
- All UK limited companies
What to File
CT600 return with full accounts
How to File
HMRC online services or commercial software
Payment Due
Different deadline - 9 months and 1 day after accounting period end
Penalties for Missing This Deadline
£100 if 1 day late, £200 if 3 months late, 10% of unpaid tax if 6 months late, further 10% if 12 months late
Filing Checklist
- Finalise your profit and loss account for the period
- Add back any disallowable expenses (entertaining, depreciation, fines)
- Calculate capital allowances (AIA, writing down allowances)
- Apply any trading losses brought forward from previous years
- Calculate Corporation Tax at correct rates (19% under £50k, marginal relief, 25% over £250k)
- Prepare tax computation workings showing the calculation
- Ensure your accounts match the figures in your CT600
- Have your company UTR and Government Gateway credentials ready
Documents You'll Need
- Profit and loss account for the accounting period
- Balance sheet as at the period end date
- Tax computation showing the CT calculation
- Capital allowances schedule (if claiming)
- Details of any director's loans
- Bank statements for reconciliation
Common Mistakes to Avoid
- Filing before paying - payment is due 9m1d, filing is 12 months
- Not claiming all eligible capital allowances
- Forgetting to add back disallowable expenses like entertaining
- Using the wrong accounting period dates
- Not including all income (bank interest, grants)
- Miscalculating marginal relief for profits between £50k-£250k
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