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Corporation Tax Computations Must Follow A Format HMRC Has Not Finished

ended 05. August 2026

Every company required to file its Company Tax Return online must prepare its Corporation Tax computations in a format HMRC publishes, down to the layout, the content and the machine-readable tagging. There was no Budget, no new statutory instrument, no press release. HMRC's Company Taxation Manual page CTM93210 was updated on 3 August 2026, and the change note reads, in full, “Addition of new rules from 31 July 2026”. By then, that date had passed.

The manual says: “From 31 July 2026, companies required to file their Company Tax Return online must prepare their computations in the format published by HMRC.” Behind it sit Commissioners' Directions under the Income and Corporation Taxes (Electronic Communications) Regulations 2003. Paragraph 6 requires computations to “conform to the format prescribed by HMRC”, and paragraph 11 states “These directions have effect from 31 July 2025.” The Direction sends companies to HMRC's Corporation Tax technical specifications page, where the document that sets out the format, “CT Computations Format” version 1.1, carries a change log that struck out its own start dates and says “for the moment there is no implementation date for the prescription”. Three documents, three answers.

The regulations let HMRC treat a return that misses its published standards of accuracy and completeness as never delivered. HMRC has not said it will. Its guidance on the Corporation Tax online service says “In most cases, no action is needed. Your software provider should implement these changes automatically”. That holds only if the software has already been built to a specification HMRC has not finished. Two sections are published, with more to follow, and HMRC's consultation on modernising company tax returns closed on 2 June 2026 with no response published. The exposure is not with large groups already filing fully tagged accounts. It is with small owner-managed businesses and their accountants, who lost HMRC's own online filing service on 31 March 2026 and picked up a stricter specification in July.

  1. Should an obligation that applies to every company required to file online be introduced through an update to an internal HMRC manual, or does a change of this reach have to be announced?
  2. Who does this actually hit hardest, and is it fair to expect the same small companies pushed onto paid software in March to meet a prescribed computation format now?
  3. What should HMRC do to clear this up, and what should companies and their accountants be doing before their next filing? Do you have a client whose plans this would change? If so, please give as much colour and detail as possible.

3 responses from the Newspage community

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Editor
Harvey Dhillon
Founder & CEO at Zmartly
Does a rule for every company required to file online have to be announced? Yes, and HMRC has just deleted the reference in its manual, not the rule it pointed to. It added that reference on 3 August 2026 and removed it a day later. A separate HMRC direction still imposes the rule. It has effect from 31 July 2025, but HMRC only spelled the format out on 8 July 2026. The big group with a tax team will absorb it. The one-director company and its accountant will not. HMRC closed its own filing service on 31 March 2026 and sent them to commercial software. Is that fair? No. HMRC should set one date and respond to the consultation it closed on 2 June 2026. HMRC's guidance says your software provider should do this for you. The duty is on your company, not your software. I will not put a client's plans in print. So ask whoever files for you what format your computations follow. HMRC says there is no start date for the format yet. Plan for the day it names one.
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Editor
Tony Redondo
Founder at Cosmos Currency Exchange
In a digital world, it sometimes pays to still be analogue. An Accountant friend advised me she calculates the CT on a spreadsheet using the CT rates. Then puts the figures into the software, and it calculates the figures again. If they match, Bingo! If they don’t match, she double checks to find and sort out the discrepancy. The bottom line. The software companies need to have software that works the way HMRC says it should work, otherwise the software company will lose its licence to provide the software.
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Editor
David Stirling
Independent Financial Adviser at Mint Wealth
As usual, the people hit hardest by all this are the small owner-managed businesses, those who lost HMRC's free filing service in March, that were pushed onto paid software and have now quietly inherited a stricter specification mid-year. HMRC's reassurance that "no action is needed" holds only if your software has been built to a standard HMRC has not finished writing. You should check with your provider now as this deadline does not share HMRC's relaxed attitude to dates.