Definition
iXBRL (inline eXtensible Business Reporting Language) is a digital format that adds machine-readable tags to each figure in a set of accounts while keeping the document readable by people. HMRC requires company accounts and Corporation Tax computations filed with a CT600 to be in iXBRL. Companies House also processes software-filed accounts in iXBRL, and from 1 April 2028 all accounts must be filed that way.
Who needs it
Companies filing a Company Tax Return online need iXBRL accounts and computations, including micro-entities and companies with a loss or no tax to pay. HMRC’s free CATO (Company Accounts and Tax Online) service closed on 31 March 2026, so companies now need commercial software or an agent. If you are weighing up doing it yourself, read what filing your own CT600 involves.
Do you tag accounts yourself?
No. Filing software or an accountant applies the tags when the accounts are produced. Not all software supports the tagging Companies House will need, so check with the provider before relying on it.
Companies House from April 2028
WebFiling and paper will stop accepting accounts on 1 April 2028, including dormant and revised accounts. Other WebFiling services, such as confirmation statements, continue.
SmartFiling’s CT600 filing service submits the return with iXBRL-tagged accounts and computations.
Related questions
- How do I file a CT600 now HMRC's free filing service has closed? Use commercial software that produces iXBRL, or have an accountant file it for you.
- Is Companies House WebFiling closing? Not entirely; from 1 April 2028 it stops accepting accounts, but other filings continue.
Related terms
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CT600
The CT600 is the Company Tax Return a UK company files with HM Revenue and Customs (HMRC) for each accounting period.
Read definition -
CATO
CATO (Company Accounts and Tax Online) was HMRC's free online service for filing a company's accounts and Company Tax Return (CT600) with HMRC.
Read definition -
Micro-entity accounts
Micro-entity accounts are the simplified annual accounts that a company qualifying as a micro-entity can prepare under the accounting standard FRS 105.
Read definition -
Corporation Tax computation
A Corporation Tax computation is the working that shows how a company gets from the profit in its accounts to its taxable total profits and Corporation Tax bill.
Read definition
