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Corporation Tax deadline calculator

Corporation Tax has two dates that people mix up: when you pay, and when you file the return. Enter the day your accounting period ends and you get both, counted from that day.

The last day of the year your accounts cover, as DD/MM/YYYY. It is on your Companies House filing or your accounts.

A worked example

A company’s accounting period ends on 31 Mar 2026.

  • Payment: 9 months after 31 Mar 2026 is 31 December 2026, and the deadline is the day after: 1 Jan 2027.
  • CT600 return: 12 months after the period end: 31 Mar 2027.

Where the month you land in is shorter than the day you started from (a period ending 31 May, say, which lands in February), the date is the last day of that month, and the payment date adds one day to it.

What this does not cover

Large companies, with taxable profits over £1.5 million, pay in quarterly instalments instead. Those dates depend on the period start and are out of scope here; see the gov.uk instalment rules. Nor does it cover accounting periods longer than 12 months, which HMRC splits into two. It is a date calculator and not tax advice.

Questions people ask

When is Corporation Tax due?

Normally 9 months and 1 day after the end of your accounting period. For a period ending 31 March 2026, that is 1 January 2027.

When is the CT600 Company Tax Return due?

Within 12 months of the end of the accounting period it covers. For a period ending 31 March 2026, that is 31 March 2027. It is a separate deadline from the payment.

Do I have to file a CT600 if there is no tax to pay?

Yes. HMRC charges late filing penalties if you do not file your Company Tax Return on time, even if there is no tax to pay.

What if the deadline falls on a weekend?

For the payment, gov.uk says to make sure it reaches HMRC on the last working day before the deadline, unless you pay by Faster Payments using online or telephone banking. This tool shows the exact calendar date and does not move it.

Does this work for large companies?

No. Companies with taxable profits over £1.5 million pay Corporation Tax in quarterly instalments with different dates. That is outside this tool; gov.uk has the rules for each band.

Sources

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