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HMRC internal manual

Company Taxation Manual

Corporation Tax: accounting periods: cannot exceed 12 months

No accounting period can be longer than twelve months but it may be shorter. For example a company may make up a six month account. There are special rules for certain retail co-operative societies, and the guidance for them is at CTM40555. If a company makes up an account for longer than twelve months, the first twelve months will normally be an accounting period.