The Director's Guide to Surviving a Missed CT600 Deadline

You are a company director. The CT600 deadline has passed. You have received a penalty notice from HMRC, or you know one is coming, and you are not sure whether to deal with it yourself or hand it to someone else.

This is the guide for that exact situation. No generic advice — just the decisions you actually need to make, in the order that matters.

First: understand what you're actually dealing with

A missed CT600 deadline is not just an HMRC issue. If your annual accounts are also late at Companies House (which happens when you miss the CT600, because the accounts are prepared from the same underlying financials), you have two regulators pursuing you simultaneously. HMRC for the tax return. Companies House for the accounts. They do not coordinate. Each issues its own penalties on its own schedule.

The CT600 is due 12 months after your accounting period end. The Companies House accounts are due 9 months after period end — three months earlier. So the accounts are typically more overdue than the CT600 even when both are missed at the same time.

The financial exposure — what you're actually facing

HMRC charges: £100 to £200 flat penalty (doubling for consecutive late years), rising to 10% of unpaid corporation tax at six months and another 10% at twelve months. On a corporation tax bill of £40,000, twelve months late means £8,000 in percentage-based penalties alone — on top of the flat charges and interest.

Companies House charges: up to £1,500 for a private company (£3,000 if the previous year was also late). These are fixed regardless of your tax liability — even a company with no turnover faces the same scale.

Director's personal liability — the part nobody mentions

Limited liability protects directors from company debts in most circumstances. Tax debts are not most circumstances. HMRC can pursue directors personally for unpaid corporation tax, PAYE, and VAT where there is evidence of deliberate non-payment or fraudulent preference — prioritising payments to other creditors while leaving HMRC unpaid.

This is not theoretical. HMRC has specific guidance on director liability and uses it. A director who allows a company to accumulate a large HMRC debt while drawing salary, paying other suppliers, or making director loan repayments is in a materially different position from one who simply had a cash flow problem.

The director's action sequence

Step one: file the Companies House accounts immediately. This stops the strike-off clock and stops the Companies House penalty from escalating further. Even draft accounts are better than nothing at this stage.

Step two: file the CT600 using the same underlying figures. Ensure consistency between the two — discrepancies between what is filed with Companies House and what is filed with HMRC create additional problems.

Step three: assess the penalty position. HMRC CT600 penalties can sometimes be appealed on reasonable excuse grounds, particularly for first-time late filings. Companies House penalties are harder to appeal but not impossible in cases of genuine and demonstrable emergency.

Step four: arrange payment or a Time to Pay plan for any outstanding corporation tax before HMRC moves to enforcement. A corporate tax specialist negotiating on your behalf secures better terms than a director negotiating directly — both because of their relationship with HMRC and because they know what information HMRC's Debt Management team needs to see.

When to use a specialist and when to DIY it

If your company is only a few months late, the accounts are straightforward (no complex transactions, no director loans, no property), and you have a clear timeline for getting everything resolved — you can probably manage this directly.

If you are more than six months late, approaching the twelve-month percentage penalty threshold, or if there are complexities in the accounts that make preparation difficult, a specialist will almost certainly save you more in penalties and interest than they cost in fees. That is not a general statement — it is arithmetic specific to your situation.