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HMRC internal manual

COTAX Manual

CT online services: CT online services overview: CT online filing

The requirements

Since 1 April 2011, companies have had to file their company tax returns electronically for all APs ending on or after 1 April 2010 using HMRC CT Online Services. A company or agent must register with CT Online Services before they can file a return.

The accounts and computations elements of such returns must be filed in iXBRL, which is an IT standard designed specifically for business financial reporting.

Since 1 April 2011, CT and CT-related payments have to be made electronically. See COM60050 for more information.

These requirements also apply to overseas companies resident in the UK, and any non-resident company trading in the UK through a permanent establishment.

Any electronic return must include all the following:

  • form CT600
  • all supplementary pages that are required
  • the accounts and computations
  • any required elections.


  • Companies that are run entirely by individuals who are practising members of a religious society or order whose beliefs are incompatible with the use of electronic communications are not required to file online.
  • Insolvent companies within a formal administration or winding up procedure are excluded from the legal requirement to file online. However, solvent companies being wound up under a members’ voluntary liquidation are not excluded from online filing.
  • Unincorporated charities, clubs and societies can choose to file their accounts in either iXBRL or Portable Document Format (PDF) but they must still file their return online and submit any computations in iXBRL format.
  • We accept accounts from smaller charities in PDF format. This is because the accounting principles by which smaller charities prepare accounts mean that the accounts part of the HMRC free service (CATO) may not be available for them. A ‘smaller charity’ for this purpose is one where, together with any wholly owned subsidiaries, that is companies owned by the charity, the combined income does not exceed £6.5 million for the accounting period.
  • Any computation forming part of a charity’s company tax return must be in iXBRL format. However, no computation is required at all where the CT600E (Charities and Community Amateur Sports Clubs (CASCs)) supplementary page of the return is completed and confirms that all income and gains of the charity are exempt from tax and have been or will be applied for charitable purposes.
  • The group accounts of group companies do not need to be iXBRL-tagged.
  • Where companies use an accounting standard which has a taxonomy that is not supported by CT Online Services, such as some overseas companies trading through a branch or agency in the UK, we accept accounts in PDF format. A taxonomy is a classification system for accounts.

Software options for delivering company tax returns

An electronic filer may deliver a return using:

  • proprietary third party software provided by a commercial company that can deliver the CT600, any of the required supplementary pages, the accounts, computations and any supporting documents
  • HMRC Corporation Tax online filing service. This application is intended for small, unrepresented companies and allows them to complete and submit a CT600 and supplementary pages CT600A, CT600E and CT600J.

A company can also use the HMRC Corporation Tax online filing service to produce the required accounts and computations in iXBRL format. However, not all companies can use the service.

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Companies that cannot use HMRC’s free filing service (CATO)

HMRC currently offers a free service for filing Company Tax Returns designed for unrepresented companies with straightforward affairs.

A company cannot use the free service if any of the following apply:

  • company accounts require an audit or have been audited
  • company turnover is above £632,000 per year
  • charity turnover is above £6.5 million per year
  • company must pay its Corporation Tax in instalments
  • company is part of a group
  • company is not registered in the UK
  • company is in liquidation or receivership
  • company is an insurance company - not including independent insurance brokers
  • company is an investment company
  • company is a credit union
  • company is a commercial property management company
  • the Corporation Tax accounting period for the return is covered by more than one set of statutory accounts
  • company needs to claim a repayment of a loan to a participator (for example, a director’s loan), more than 9 months after the end of the accounting period

A company cannot use the free service if they need to report any of the following in the accounts:

  • called up share capital not paid
  • contingent assets
  • financial instruments
  • income or expenditure from investment assets
  • foreign income and currency transactions
  • the costs of restructuring
  • share-based payments
  • share premium
  • adjustments for something reported in a previous year

A company cannot use the free service if they need to include any of the following in the computations:

  • chargeable gains or losses
  • Research and Development (R&D) costs
  • capital allowances, other than the specific plant and machinery, AIA and low emission cars
  • non-trading income (except interest received)
  • complex loan-relationship entries
  • leased cars
  • foreign trade income.

Companies can find all this information on the HMRC website

The new online service asks the company questions to work out whether they can use the service. If they can’t, they will be directed to the use third party software.

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Common questions asked by companies and agents

Companies and agents may have questions about online filing. See Tax Service Corporation Tax FAQs for guidance on how to answer some of the more common queries.

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Further action or review of online filed returns

If COTAX identifies that you need to take further action to process or review an original return filed online, it enters the case on EFRL (E Filed Returns List).

It enters amended returns that are filed online on AEFL (Amended E-Filed List) only where you need to take further action.