Daniel Nazarian

Thank you for the response above, but I don’t think it directly addresses my query. I’m seeking clarification of the meaning on terms such “within 18 months” specifically as applied to an accounting period ending on the last day of a calendar months with only 30 days.
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In the example above, in normal circumstances, Paragraph 18(1) Schedule 18 FA 1998 would trigger a liability for a tax-related penalty if a return is not filed “within 18 months after the end of the accounting period”.
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But if the end of the accounting period falls at the end of a calendar month with 30 days – e.g. 30 April 2023, it is not clear whether the period of “18 months” runs up to *30th* October 2024 (i.e. the 30th day of the calendar month that is 18 months later) or *31st* October 2024 (i.e. the end of the corresponding calendar month). Put another way, in this example, the question is would a filing made on 31 October 2024 be “within 18 months”.
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I have searched for HMRC’s manual for guidance on this specific point, but I have not located an answer.

Under Paragraph 18 of Schedule 18 FA 1998, a company can be liable to a tax-related penalty if it fails to file its corporation tax return within 18 months after the end of the accounting period. I am trying to determine how this 18-month rule works in practice when the relevant accounting period ends at the end of a calendar month with fewer than 31 days. // For example, for a corporation tax customer with an accounting period ended 30th April 2023, my question is does the 18 month period run up to 30th October 2024, or does it run to 31st October 2024 instead? // On a similar note, in certain circumstances section 104AA CTA 2009 can restrict the ability for a company to make a claim for R&D expenditure credit (‘RDEC’) if it fails to make a claim notification within the ‘claim notification period’. Per section 1142A CTA 2009, the ‘claim notification period’ ends with “the last day of the period of six months beginning with the first day after” the period of account. For a corporation tax customer with a period of account ended 30th June 2024, does the claim notification period run up to 30th December 2024 or 31st December 2024?