Corporation tax late filing
The fixed penalties doubled in April 2026, and the filing date, not the accounting period, decides which side of the line a return sits. The percentages did not move: 10% of the unpaid tax at six months, another 10% at twelve. A nil return still collects the fixed amounts, and a third late year in a row raises them fivefold.
The four steps
already charged at this lateness still ahead
Fixed amounts doubled for filing dates on or after 1 April 2026, Autumn Budget 2025 amendments to Sch 18 FA 1998; verified against gov.uk (page updated 24 April 2026), checked 18 July 2026.
The filing date is the dividing line: returns with a filing date on or after 1 April 2026 sit in the new regime even where the accounting period ended before it. The filing date is twelve months after the end of the accounting period, or the Companies House date where an extension pushes it later. A penalty notice can arrive months after the lateness began; the liability arises on the day, not on the notice. The statutory clocks run in calendar months; the slider counts days, so a boundary can sit a day or two either side of the real one.
At six months HMRC estimates the bill, a tax determination: there is no appeal against it, only displacement by filing the actual return, and the 10% steps are calculated on the tax still unpaid. Where the return stays out, the second 10% lands at twelve months on the same basis.
Corporation tax itself has no late payment penalty: the tax was due nine months and one day after the period end, before the return, and paying late costs interest at a rate tied to the Bank of England base rate, but no percentage charge. The percentages on this page hang off the missing return. The Companies House clock on the accounts runs separately. Whether an excuse is reasonable is HMRC’s judgment and then the tribunal’s, and none of it is arithmetic. How we check these numbers.