Corporation tax penalties come in two families that are often confused. Late filing penalties are for the return, the CT600, and are charged even where there is no tax to pay: fixed amounts on the first day and at three months, then a percentage of the unpaid tax at six and twelve months, per gov.uk. Late payment is handled differently: HMRC charges interest on the unpaid tax from the due date, and penalties for late payment of corporation tax itself arise mainly through the instalment regime and tax determinations. This page sets out both, with the figures as gov.uk publishes them, how an appeal works and what counts as a reasonable excuse, and the dates that avoid all of it, which the free tools on this site keep against the company.
Corporation tax late filing penalties
Per gov.uk: £200 if the return is one day late, another £200 at three months, then at six months HMRC estimates the corporation tax and adds a penalty of 10 percent of the unpaid tax, and at twelve months another 10 percent of any tax still unpaid. If the return is late three times in a row, the £200 fixed penalties rise to £1,000 each. The penalties attach to the return, so a company with no tax to pay that files late still owes the fixed amounts, and a company that files on time but pays late owes none of them.
Late payment: interest, and the determination
Corporation tax paid after the due date, nine months and one day after the period end, carries late payment interest at 7.75 percent from 9 January 2026, per gov.uk's published rates, running daily from the due date to the date paid. Interest is not a penalty and cannot be appealed on its own. Where a return is six months late HMRC issues a tax determination, its own estimate of the tax, which cannot be appealed; the company must pay it and file the return, after which HMRC recalculates the tax, the interest and the penalties on the real figures.
The appeal, and what a reasonable excuse is
A late filing penalty can be appealed online if the company has a reasonable excuse, but only after the return has been filed, per gov.uk. The appeal needs the UTR, the date and amount on the penalty notice and the period end, and it is completed in one sitting and posted. A reasonable excuse is something outside the company's control that stopped it filing, such as a serious illness or a failure of HMRC's own service; relying on an accountant who did not file, or not having the money, is not one. An appeal that arrives before the return does is refused.
The calendar that avoids all of it
Two dates per accounting period: the payment date at nine months and one day, and the filing date at twelve months. A company that pays on the earlier date and files on the later one owes no penalty and no interest, and a company that files early does not bring the payment date forward. The free UK corporation tax calculator on this site works the amount; Dividvo Pro keeps both dates against the year and reminds you before each, which is worth more than any page about penalties.
Questions people ask about corporation tax penalties
Is there a penalty for paying corporation tax late?
For a small company outside the instalment regime the cost of paying late is interest at 7.75 percent from the due date, per gov.uk, rather than a fixed penalty. Penalties attach to the return, and to instalment failures and determinations for larger companies.
Can I appeal the interest?
No. Interest is compensation for the late payment rather than a penalty and there is no appeal against it. What can be appealed is the penalty, and only with a reasonable excuse.
Do the penalties apply to a dormant company?
Only if HMRC has issued a notice to deliver a return. A company that HMRC has agreed is dormant does not receive the notice and has no return to file late. A company that is dormant but has not told HMRC still receives the notice and is penalised for ignoring it.