Corporation Tax deadline calculator

When do you have to pay Corporation Tax?

GOV.UK says you must pay your Corporation Tax 9 months and 1 day after the end of your accounting period. For a year ending 31 March 2026, that is 1 January 2027. You pay HMRC directly, and the payment date comes before the filing deadline. GOV.UK: Pay your Corporation Tax bill.

Large companies pay earlier, by instalments. If your taxable profits are between £1.5 million and £20 million you usually pay in quarterly instalments, and companies with profits over £20 million follow separate rules for very large companies. The £1.5 million threshold is divided by the number of associated companies plus your company, and a company whose profits are no more than £10 million may not have to pay by instalments in the first year it is large. This calculator does not work out instalment dates — see GOV.UK: Corporation Tax paying in instalments.

When is the CT600 filing deadline?

The deadline for your Company Tax Return is 12 months after the end of the accounting period it covers — 31 March 2027 for a year ending 31 March 2026. You must file a return if HMRC sends the company a "notice to deliver a Company Tax Return", and HMRC charges a penalty if you file late. GOV.UK: Company Tax Returns · GOV.UK: Penalties for late filing. Our guide explains what happens if you file your CT600 late.

When are accounts due at Companies House?

Unless they are its first accounts, a private company has 9 months from its accounting reference date to deliver its accounts to Companies House — 31 December 2026 for an accounting reference date of 31 March 2026. The period ends on the matching date 9 months later, except that when the accounting reference date is the last day of a month it runs to the last day of the month: an accounting reference date of 30 April gives until 31 January, not 30 January.

First accounts that cover more than 12 months must be delivered within 21 months of the date of incorporation, or 3 months from the accounting reference date if that is longer. Companies House's example: a private company incorporated on 1 January 2025 with an accounting reference date of 31 January has until 1 October 2026. The deadlines apply even when they fall on a weekend or bank holiday. Companies House: Life of a company – accounts.

What if your accounts cover more than 12 months?

A Corporation Tax accounting period cannot be longer than 12 months, so accounts covering a longer period need two Company Tax Returns: one for the first 12 months and one for the rest. Each period has its own payment date, and GOV.UK's example of a lengthened year files all the returns by 12 months after the end of the accounts period. A year end can be extended to a maximum of 18 months (longer only for a company in administration). GOV.UK: Accounting periods for Corporation Tax · GOV.UK: Change your company's year end.

GOV.UK's first-accounts example is a company set up on 11 May 2024 whose first accounts run to 31 May 2025:

Corporation Tax accounting period	Pay by	File by
11 May 2024 to 10 May 2025	11 February 2026	31 May 2026
11 May 2025 to 31 May 2025	1 March 2026	31 May 2026

If your company started doing business after it was set up, its first accounting period starts when business started, and HMRC writes to tell you the dates. GOV.UK: Your company's first accounts and Company Tax Return. Our guide explains why first accounts may need two CT600s.

How does this calculator work out the dates?

• Payment: the day after the date 9 months after the accounting period ends, for each accounting period when the accounts cover more than 12 months. A period ending on the last day of a month counts to the last day of the ninth month, and a date that doesn't exist (such as 30 February) becomes the last day of that month, as in HMRC's Company Taxation Manual (CTM01800).
• CT600 filing: 12 months after the end of the accounts period, using the same month-end rule: a period ending 28 February 2027 is due on 29 February 2028, and one ending 29 February is due on 28 February the next year (CTM93040).
• Companies House: 9 months after the period end, which we treat as your accounting reference date, using the month-end rule above. If Companies House holds a different accounting reference date for your company, count from that date instead.
• First accounts at Companies House: when the accounts cover more than 12 months we can't tell whether they are the company's first, so we show two dates — the first-accounts deadline (21 months after the start date you entered, taken as the date of incorporation, or 3 months after the period end if that is later) and the 9-month deadline for an extended later period.
• It assumes a private limited company that is not paying by instalments.

Deadlines are only half the job. Taxley prepares the CT600, tax computation and iXBRL accounts and files the return to HMRC — take the 30-second check to see if it suits your company, or read the Corporation Tax glossary if a term here is new.

Frequently asked questions

Do I pay Corporation Tax before I file the CT600?

Usually, yes. For a company that doesn't pay by instalments, Corporation Tax is due 9 months and 1 day after the end of the accounting period, but the CT600 isn't due until 12 months after it. So the payment deadline comes about three months before the filing deadline.

Does a weekend or bank holiday move the Companies House deadline?

No. Companies House says its accounts deadlines apply even when they fall on a weekend or a bank holiday, so plan to file before the date rather than on it.

What happens if I miss the CT600 filing deadline?

HMRC charges a penalty for filing late, which grows the later the return is. After 6 months HMRC can also estimate the tax it thinks you owe (a tax determination). Paying late is separate: HMRC may charge interest if you don't pay by the payment deadline.

Are the deadlines different for my first accounts?

Often. First accounts usually cover more than 12 months, which means two Corporation Tax periods, two CT600 returns and two payment dates. The Companies House deadline for first accounts covering more than 12 months is 21 months after incorporation, or 3 months after the accounting reference date if that is later.