Overdue accounts
The company tax return is due twelve months after the end of the accounting period, but the tax itself was due three months before that. A late return usually means interest is already running, and if HMRC has issued a determination, a figure has been set without you.
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QuickBooks PartnerCertified ProAdvisor100+ yearsCombined team experienceFully insuredUp to £2m indemnityFile the outstanding CT600 with the accounts and computations as soon as possible. Penalties start at £100 and reach 10% of the unpaid tax at six months and a further 10% at twelve. An HMRC determination can only be displaced by filing the actual return, and normally within three years of the filing deadline.
Do this first. Check whether HMRC has issued a determination of tax for the period. If it has, the clock on replacing it is limited, and filing the real return is the only way to do it.
Corporation tax is payable nine months and one day after the end of the accounting period. The return telling HMRC how much that was is due three months later, twelve months after the period end. Paying late and filing late are charged separately: interest on the tax, penalties on the return.
Large companies paying by quarterly instalments have a different payment pattern, but the return deadline is the same.
Where no return arrives, HMRC can determine the tax itself. The determination is legally enforceable and cannot be appealed; the only way to displace it is to file the actual return. There is a time limit on doing so, generally three years from the statutory filing date, after which the determined figure stands even if it is far too high.
Determinations are usually estimated on the high side, so this is the situation where filing quickly has the most direct financial effect.
A CT600 cannot be prepared properly without the statutory accounts for the same period, because the computation starts from the accounting profit and adjusts it. Where both are outstanding we prepare the accounts, file them at Companies House, and submit the return with the accounts and computations attached in iXBRL as HMRC requires.
File the return anyway. The tax-geared penalties are calculated on unpaid tax at six and twelve months, and a time to pay arrangement is far easier to agree once HMRC has a real figure in front of it rather than an estimate. Interest continues to run under an arrangement, but enforcement action normally stops.
Rates, penalties and thresholds quoted on this page are those in force for the 2026/27 tax year and for accounting periods filed under the current Companies Act and Finance Act rules. They are general information about how the filing regime works, not advice on your company's position. Penalties and interest depend on the dates on your own filing record, so send us the details before acting.
Questions
HMRC's own filing service only covers the current and two previous accounting periods, and needs the accounts tagged in iXBRL. Older periods generally need commercial software, which is one of the practical reasons old returns get left.
Yes. The fixed £100 penalties apply regardless of whether tax is due, and a loss you never reported cannot be carried forward against future profits until the return establishing it is filed.
HMRC will cancel a penalty where there is a reasonable excuse: serious illness, bereavement, a genuine service failure. It must be evidenced and the return must be filed without unreasonable delay once the excuse ends.
Not automatically, but a late return extends the window in which HMRC can open one, and a determination replaced at the last minute attracts more attention than a return filed promptly.
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