Free tool · 2026/27 rates
Late filing penalty estimator: Self Assessment, Corporation Tax and Companies House
Filing penalties in the UK are automatic and escalate with time, and most people underestimate them because the headline £100 is only the first step. This estimator takes the type of filing, the statutory deadline, the date you expect to file and, where relevant, the tax owed, and shows the penalties that would apply at each stage. It covers the three filings small businesses are most often late with: the Self Assessment return, the company tax return (CT600) and the statutory accounts due at Companies House. It does not include interest on late-paid tax or the separate late-payment penalties, which are charged on the tax itself regardless of when the return goes in.
Self Assessment penalties
A return filed after 31 January attracts £100 immediately, whether or not tax is due. From three months late, daily penalties of £10 run for up to 90 days, adding up to £900. At six months a further penalty of the greater of £300 or 5% of the tax due applies, and at twelve months another of the same amount, rising to up to 100% of the tax where the failure is deliberate. Separately, tax paid late attracts interest from the due date and late-payment penalties of 5% at 30 days, six months and twelve months.
Corporation Tax return penalties
A CT600 filed late attracts £100, rising to £200 after three months. These fixed penalties increase to £500 and £1,000 for a company that has been late three times in a row. At six months HMRC charges 10% of the unpaid tax, and at twelve months a further 10%. Corporation Tax itself is due nine months and one day after the year end, with interest from that date.
Companies House penalties
Private company accounts filed up to one month late cost £150, up to three months £375, up to six months £750, and more than six months £1,500. Where the previous year's accounts were also filed late, the penalty is doubled. These are civil penalties that Companies House rarely waives, and persistent failure leads to compulsory strike-off and can lead to director disqualification. Confirmation statements carry no fixed penalty but late filing is an offence and triggers strike-off proceedings.
Appeals
HMRC accepts a reasonable excuse, such as serious illness, bereavement or a failure of HMRC's own systems, provided the return was filed as soon as the excuse ended. Being too busy, not knowing the rules, or relying on someone else who let you down are generally not accepted, though reliance on a competent adviser can be. Companies House accepts appeals only in exceptional circumstances. The estimates here use the 2026/27 penalty rules and are not advice; see the advice disclaimer.
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