What counts as late filing under CT600 rules
All UK limited companies must file a Company Tax Return (CT600) for each accounting period. HMRC’s rules are clear: if the return arrives late — even if no tax is due — penalties start straight away. GOV.UK+1
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1 day late: £100 fine
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3 months late: another £100
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6 months late: HMRC may issue a “tax determination” — assessing what you owe — plus a 10% surcharge on any unpaid tax
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12 months late: further surcharges apply
Late payment of any due tax compounds the problem with interest and additional charges.
Why late filing often hits small businesses hardest
For many small companies, income and profits can fluctuate — particularly where contracts, invoicing or cash flow are unpredictable. Without consistent bookkeeping, it’s easy to miss filing or payment deadlines.
Furthermore, absent robust records, estimating what you owe becomes guesswork — increasing the risk of under-payment or surprise bills.
How organised bookkeeping avoids CT600 penalties
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Maintain up-to-date books throughout the year so you always know profit and likely tax liability
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Set reminders ahead of the filing deadline (typically 12 months after your accounting period end)
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Estimate the tax early; if funds are tight, consider scheduling part-payment or a Time-to-Pay request rather than leaving deadlines to the last minute
Staying ahead gives you financial control, avoids surprise bills and keeps your company compliant — crucial for long-term stability and growth.
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