What is iXBRL?
Inline XBRL is the tagging format HMRC and Companies House both require — here's what that actually means, in plain language.
The short version
iXBRL (Inline eXtensible Business Reporting Language) embeds machine-readable tags directly inside a normal-looking HTML document. Open the file in a browser and it reads like ordinary accounts — the tags sit invisibly underneath, letting HMRC's and Companies House's systems identify each figure automatically instead of a person retyping it.
Why "inline"?
Older XBRL implementations kept the tagged data in a separate file from the human-readable report. iXBRL combines both into one document — one file to prepare, one file to file, one file that looks right to a person and validates correctly to a machine.
What a tag actually does
Each figure in your accounts gets wrapped in a tag mapped to a standard taxonomy element — for example, your turnover figure gets tagged as uk-gaap:Turnover, so any system reading the file knows precisely what that number represents, not just that a number appears near the word "turnover."
Not a UK invention
XBRL is a global standard maintained internationally, used in some form by dozens of regulators. The US SEC has required Inline XBRL since 2018; other countries use non-inline XBRL variants for their own company registries.
Where iXBRL applies in the UK
Two separate regulators require it, for two separate documents: HMRC for your CT600 Company Tax Return, and Companies House for your annual accounts. See what to file in iXBRL for the full breakdown by document type.
Who actually has to file?
See who must file iXBRL — and if you're not sure it applies to you at all, who doesn't need to file.
Frequently asked questions
Is iXBRL the same as XBRL?
iXBRL is a variant of XBRL. XBRL is the underlying data-tagging standard; iXBRL (Inline XBRL) embeds those tags inside a normal-looking HTML document instead of a separate data file, so one document works as both the human-readable report and the machine-readable filing.
Do I need special software to open an iXBRL file?
No — an iXBRL file opens in any web browser and looks like ordinary accounts. The tags are embedded in the underlying code and are only read by the systems processing your filing, not visible to someone simply viewing the document.
Is iXBRL only used in the UK?
No. XBRL and its inline variant are used by regulators in dozens of countries, including the US SEC (Inline XBRL since 2018). The UK's specific requirements come from HMRC and Companies House, but the underlying tagging concept is international.
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