HMRC iXBRL filing – corporation tax return

Company Tax Returns – UK

HMRC (HM Revenue and Customs) is the department of the UK Government responsible for the collection of taxes.

If you have to prepare accounts under the Companies Act, you must file your accounts and computations online in iXBRL format.

Company Tax Return

A Company Tax Return comprises:

  • Company Tax Return (CT600 form) including any required supplementary pages
  • Statutory company accounts
  • Corporation Tax computations

 .... together with any other attachments (in PDF format) to support your return.

Therefore if you have to prepare accounts under the Companies Act, you must file these online in iXBRL format.

Filing your return – 2 options

There are 2 options for filing your accounts and company tax return online with HMRC:

Option 1 – HMRC

  • File with HMRC's online filing service which allows you to generate the CT600, accounts and computations – check if you can use the HMRC Corporation Tax online filing service
  • It is a free service that can be used by many small unrepresented companies with relatively straightforward financial affairs to file their returns online
  • Unfortunately the uploading/attaching of iXBRL files for accounts and/or computations is not supported by the service
  • For straightforward applications HMRC's CATO (Company Accounts and Tax Online) online service can be utilised to file a tax return for your company, charity or association:

Option 2 – use commercial filing software

Submitting iXBRL – the files you receive from us

Before we deliver to you

Before delivery to you, the iXBRL file is fully validated with HMRC, so that no issues during filing are encountered.

Uploading the iXBRL file(s) to HMRC

On receipt from us, you then attach the iXBRL format file for your accounts or computations within the filing software – these iXBRL files are supplied by our Tagging Service.

iXBRL file name has an HTML

The iXBRL file supplied by us has a .html extension  e.g. Acme_Enterprise_plc_UK_acct_20211231_01a.html  – this iXBRL file is attached to the return.

View it in a browser

The fact that the iXBRL file has an .html extension means that you can click on the file and see a visual representation of the financial statement within a browser. 

The file appears to be just an ordinary HTML file, which can be a cause of confusion.  However, rest assured that the iXBRL code itself is contained within the file (although the iXBRL code is not visible when simply viewed within a browser).

What about the PDF file you supplied?

The Tagging Report supplied as a PDF file to you is for your benefit and reference only, so do not upload/supply this to HMRC.

HMRC validation – Will the iXBRL file that you supply be accepted by HMRC?

Yes it will.  All deliverables are fully checked and validation is performed before delivery to the customer – for UK customers your file is specifically tested with the HMRC validation service, so that you do not face any issues during filing.

Additional files forming part of the return

You can only include one iXBRL accounts file and one computation file as part of your online Company Tax Return.  Any additional supporting documents forming part of the online return that you wish to send to HMRC must be attached as PDF files. 

Who can submit the iXBRL file to HMRC?

The validated iXBRL file is provided by us to you before submission, but only the registered taxpayer or the taxpayer's authorised agent can actually file the accounts.

Filing your HMRC return – the process in detail

The tax return

There are three components to the tax return:

  • Accounts – which can be submitted as a separate iXBRL accounts file
  • Computations – which can be submitted as a separate iXBRL computations file
  • CT600

Help and more information from HMRC

For assistance with filing your company tax return online, see guidance below or contact us direct:

Filing software – supports attaching iXBRL files

HMRC's Corporation Tax online service does not support the attaching/uploading of iXBRL files for either company accounts and/or computations.  Instead one needs to use commercial filing software to achieve this:

  • If you are looking for a low-cost filing software solution, a possible supplier is Andica CT600 Corporation Tax Returns Software – the iXBRL accounts and/or computation files generated by our conversion service can be attached to the CT600 return and submitted online to HMRC using the Andica File by Internet feature – more information ....

HMRC – resources

See HMRC information resources.

Long period accounts and short period accounts

Long periods accounts help

The period that a company prepares accounts for (period of account) can be longer than 12 months.

However, the Corporation Tax accounting period (AP) cannot exceed 12 months.

Where the period of account does exceed 12 months, it must be split into more than one AP, with a separate set of tax computations and form CT600 for each.

The accounts should be attached for the first AP they cover, then none attached for the other APs covered.

The trading profits need to be apportioned between the APs. This may be done by time-apportionment, which is the most common method. However, a different method should be used if better information is reasonably available. Chargeable gains fall into the AP in which they arise instead of being time-apportioned.

If the company has prepared accounts for a period that is more than 12 months but less than 18 months, it must deliver a tax return within 12 months from the end of that period. If the period of account is more than 18 months, a tax return must be delivered within 30 months from the start of the period.

More information on accounting periods, go to: Accounting periods for Corporation Tax

FAQs (frequently Asked Questions)

Further information relating to the filing of company accounts and computations is detailed in our FAQs Overview - HMRC section