A Practical Guide to HMRC iXBRL Tagging for CT600 Forms – Fin-X Solutions

HMRC iXBRL Tagging

The CT600 Form

The CT600 form is used by companies incorporated in the UK to file their Corporation Tax Returns to the HMRC after the end of their accounting period. At present, this period is stipulated to be no later than 12 months after the end of a company’s accounting period. The form includes information related to accounts, computations, reports, and statements furnished by the taxpaying entity.

Any Corporation Tax that is payable to the HMRC is due after 9 months and 1 day following the end of the accounting period. The CT600 is only capable of reporting for 12 months, so if a company’s accounting period is longer, then two CT600 forms need to be filed, one for the 12 months, and another for the remainder of the period.

Paid by companies in the UK as a percentage of their profits, Corporation Tax is a function of the total turnover for a given financial year minus operating expenses. It currently stands at 19% for the financial year beginning April 2022 but is liable to change from time to time.

With the HMRC requiring digital submissions of the CT600 form, the original paper form is now obsolete and only used for reference purposes. The HMRC also requires full company accounts to be provided in Inline XBRL (iXBRL), tagging key information that enables the document to be both machine and human-readable. In contrast to the CT600 return, company accounts can cover an accounting period greater than 12 months.

Now let’s take a look at what constitutes the CT600 form.

The Components of a CT600 Form

The latest version of the CT600 Form for 2022 (version 3) consists of 5 main sections:

  • Company information
  • Return information
  • Tax calculation
  • Declaration, and
  • Supplementary information

Let’s take a brief look at these sections.

Company Information

The company information section of the CT600 form consists of 4 fields:

  • Company name
  • Company registration number
  • Tax reference (UTR)
  • Type of company

Image 1.1.: Company information section of the CT600 form

The company registration number is a unique identification number that is obtained after registering your company with Companies House. At the time of writing, you will be registered for Corporation Tax at the same time as you register your company with Companies House.

Alternatively, if you’re already registered with Companies House but not for Corporation Tax, you can sign in to your business tax account by using your Government Gateway user ID and password to sign in. If you do not have one, you can create one when you sign in.

You must register for Corporation Tax within 3 months of starting to do a business. Failing to do so in time may incur a penalty. More registration information can be found here.

The Unique Taxpayer Reference (UTR) is a 10-digit number that you receive from the HMRC within 2 weeks of incorporation with Companies House. If you did not receive one, you can request one from HMRC and receive a copy by post to your company’s registered address.

Corporation Tax is paid to the HMRC on profits from doing business as:

  • A limited company
  • Any foreign company with a UK branch
  • Any club, cooperative, or other unincorporated association viz. a community group or sports club

Return Information

The return information section of the CT600 form starts with the start and end dates of your accounting period. As mentioned before, accounting periods longer than 12 months require two filings of the form with the HMRC.

Among other particulars, this section contains questions about transfer pricing, accounts and computations as well as a host of supplementary pages.

Tax Calculation

This is the most critical and longest section of the CT600 and broadly contains fields related to the following information:

  • Turnover
  • Income
  • Chargeable gains
  • Profits before deductions and reliefs
  • Deductions and reliefs
  • Reliefs and deductions in terms of tax
  • Coronavirus support schemes and overpayments
  • Calculation of tax outstanding or overpaid
  • Tax reconciliation

In addition to these, you will find sections on information about enhanced expenditures like Research and Development (R&D) and creative expenditures, land remediation expenditures and capital allowances, and balancing charges among others.


As the name suggests, this section is used to pronounce the correctness and completeness of all the information provided in the above sections while acknowledging that falsifying or concealing any information may lead to legal action.

Supplementary Information

This section is used for providing documentary evidence (should the need arise) to support any of the accounting and computational information provided by the filer above. PDF documents are accepted by HMRC for this purpose.

Getting the IRmark

Once the form is filled and all errors have been resolved, you are ready to submit your filing to the HMRC. A successful filing with the HMRC results in the generation of an IRmark. This is an alphanumeric string that helps a taxpaying entity prove if their submission held by the HMRC is correct.

An unsuccessful filing would result in a message from the HMRC with a list of errors and the reasons why the submission failed.

Submitting the CT600 successfully with HMRC

As the entire filing process can seem overwhelming at first, involving the conversion of financial statements to iXBRL, a lot of companies outsource this activity to a certified vendor.

Fin-X Solutions® is an HMRC-recognised iXBRL managed tagging services vendor and application provider offering a compelling choice for UK companies to outsource their iXBRL tagging and conversion process. We have been involved with XBRL filings in the UK for over a decade and provide our product and services in many other jurisdictions including the US, Ireland, the EU, South Africa, the Middle East, Malaysia, and many more.

File high-quality iXBRL CT-600 documents on time with Fin-X Solutions