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Corporation Tax Return (CT600) Deadline

CT600 return filing deadline - 12 months after your accounting period ends

12 months after accounting period end
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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