Corporation Tax UK-wide

Corporation Tax annual compliance checklist

Year-end checklist to verify your Corporation Tax compliance is complete.

Guide summary

Pay your Corporation Tax within 9 months and 1 day of your accounting period ending. File your Company Tax Return (CT600) within 12 months. Follow this checklist at the end of each accounting period to avoid penalties and lost tax relief.

  • Pay Corporation Tax by 9 months + 1 day after period end
  • File CT600 return within 12 months of period end
  • Finalise accounts using UK GAAP or IFRS
  • Claim capital allowances in the correct order
  • Check loss relief options before filing deadline
  • Review director loan accounts – Section 455 tax at 33.75%
  • Prepare and file accounts in iXBRL format
  • File accounts at Companies House within 9 months
  • Keep all Corporation Tax records for at least 6 years
  • Late filing penalty starts at £200 automatically
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Annual Corporation Tax checklist

Use this checklist to verify your Corporation Tax compliance at the end of each accounting period. Missing any of these steps can result in penalties, interest, or lost tax relief.

  1. 1

    Finalise your accounts

    Ensure your company accounts are complete and accurate. Accounts must comply with UK Generally Accepted Accounting Practice (UK GAAP) or IFRS. These form the basis of your CT600 return.

  2. 2

    Review capital allowances

    Identify all qualifying capital expenditure during the accounting period. Claim AIA, full expensing, and writing down allowances in the correct order to maximise relief.

  3. 3

    Check loss relief options

    If your company made a trading loss, consider whether to carry it back (12-month standard, 36-month terminal), carry it forward, or surrender it as group relief. Elections must be made within the CT600 filing deadline.

  4. 4

    Review director's loan accounts

    Check whether any director or shareholder owes the company money at the year end. Outstanding loans trigger Section 455 tax at 33.75% on amounts over the threshold.

  5. 5

    Consider R&D tax relief

    If your company undertook qualifying R&D, gather documentation and submit the Additional Information Form to HMRC before including the claim on your CT600.

  6. 6

    Check associated companies

    Count your associated companies to determine the correct CT rate thresholds and whether quarterly instalment payments are required.

  7. 7

    Prepare iXBRL accounts

    Your accounts must be filed in iXBRL (inline eXtensible Business Reporting Language) format with your CT600. Most commercial software handles this automatically.

  8. 8

    File your CT600 on time

    Submit your Company Tax Return within 12 months of the end of the accounting period. Late filing incurs automatic penalties starting at £200.

  9. 9

    Pay Corporation Tax on time

    Pay within 9 months and 1 day of the accounting period end (or in quarterly instalments if applicable). Interest runs from the day after the deadline.

  10. 10

    File accounts with Companies House

    Private companies must file accounts at Companies House within 9 months of the accounting reference date. This is a separate obligation from HMRC filing.

  11. 11

    Retain records

    Keep all Corporation Tax records for at least 6 years from the end of the accounting period. This includes accounts, receipts, bank statements, and correspondence with HMRC.

Key deadlines summary

For an accounting period ending 31 March 2025:

  • Pay Corporation Tax: 1 January 2026 (9 months + 1 day)
  • File accounts at Companies House: 31 December 2025 (9 months)
  • File CT600 with HMRC: 31 March 2026 (12 months)

Remember: the payment deadline comes before the filing deadline. Do not wait until you file the CT600 to pay.

Penalty risk

Late filing penalties

Penalty: 20% of unpaid tax plus £2,000 in flat penalties
<p>CT600 late filing penalties are automatic:</p>
<ul>
<li><strong>1 day late:</strong> £200</li>
<li><strong>3 months late:</strong> Another £200</li>
<li><strong>6 months late:</strong> HMRC estimates your tax and adds 10% of the unpaid amount</li>
<li><strong>12 months late:</strong> Another 10% of unpaid tax</li>
</ul>
<p>If your CT600 is late 3 times in a row, the £200 penalties increase to £1,000 each.</p>

Enforced by: HMRC

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