Corporation tax has the unusual property that the money is due before the return that calculates it. GOV.UK sets the rule out directly: you must pay your Corporation Tax 9 months and 1 day after the end of your accounting period. The return itself is not due until twelve months after that date, which means most companies pay an estimate first and file the arithmetic afterwards.
Nine months and one day, for most companies
For taxable profits of up to £1.5 million, the deadline is nine months and one day after the end of the accounting period. A company with a 31 March year end pays on 1 January. A company with a 31 December year end pays on 1 October. The accounting period is usually the company's financial year, but in the year a company is set up there are often two accounting periods, because a period for corporation tax cannot exceed twelve months while the first set of accounts frequently covers longer. Each of those periods carries its own deadline and its own payment reference.
Above £1.5 million the rule changes entirely
A company with taxable profits of more than £1.5 million does not get the nine months and one day. It pays in instalments, and the first of those falls due during the accounting period rather than after it. There are two instalment regimes, one for profits between £1.5 million and £20 million and a different and earlier one above £20 million. The £1.5 million threshold is itself divided by the number of associated companies, which is how a group of modestly sized companies can find itself in the instalment regime without any single company looking large.
The payment deadline is not the filing deadline
These are two different dates with two different penalty regimes and they are three months apart. The company tax return is due twelve months after the end of the accounting period; the tax is due nine months and one day after it. Late filing brings fixed penalties that escalate with time. Late payment brings interest, which runs from the day after the due date. A company that files early gets no payment extension, and a company that pays on time but files late is still penalised.
Questions people ask about when do you pay corporation tax
When is corporation tax due?
Nine months and one day after the end of the accounting period, for companies with taxable profits up to £1.5 million. Above that, corporation tax is paid in instalments starting during the accounting period.
Do I pay before or after I file the return?
Before, for most companies. The payment falls due at nine months and one day; the return is not due until twelve months after the period end, so the payment is usually made on a computed figure ahead of filing.
Why do I have two accounting periods in my first year?
Because a corporation tax accounting period cannot be longer than twelve months, while a first set of accounts often covers more. The longer period is split, and each part has its own deadline and payment reference.