HMRC corporation tax deadlines – meaning of “within 18 months” and “period of six months”

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?

Hi ,

Tax Related Penalites  If a company fails to deliver a company tax return for an accounting period: • within 18 months after the end of the accounting period, or • if the filing date is later than 18 months after the end of the accounting period, by the filing date,it is liable to a tax-related penalty. When a notice to deliver is given late, or there is a short accounting period at the beginning of a long period of account, the filing date may fall after the 18-month point. In this case, the company incurs no tax-related penalty provided it delivers its return by the filing date. The unpaid tax is the amount of the tax payable by the company for the accounting period that remains unpaid on the date that the company first incurs a tax-related penalty. This is the later of: • 18 months plus one day after the end of the accounting period, and • the filing date. R&D A claim to R&D can only be made in a Company Tax return or an amended company tax return. For accounting periods which commenced before 1 April 2023, a claim to R&D can be made within the normal time limit of 12 months following the filing date. For a standard 12-month accounting period this will be 2 years from the last day of that accounting period. For accounting periods which commence on or after 1 April 2023, a claim to R&D can be made: within 2 years beginning with the last day of the period of account, in a case where the period of account to which the claim relates is not longer than 18 months, or 42 months beginning with the first day of the period of account, in any other case. Thank you .

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.

Hi Daniel Nazarian
If the guidance/legislation states months, we use months as a whole unit despite the amount of days in the individual months.
So, for example if your accounting period ended on the 28/02/2023, you have until 28/02/2024 to file. 
Flat rate penalties will become due 01/03/2024 and 01/06/2023.
This means that the 18 months would take this company to the 31/08/2024, which means tax related penalties will be charged from the 01/09/2024.
Thank you