What is iXBRL, and does your company need it?
iXBRL (inline eXtensible Business Reporting Language) is a way of writing accounts so they read like a normal document to people, while every figure carries a hidden tag a computer can read. HMRC requires it for the accounts and computation sent with a Company Tax Return, and Companies House will require it for all accounts from April 2028.
- An iXBRL file is a web page of your accounts with a machine-readable tag on each figure.
- HMRC needs your accounts and tax computation in iXBRL with every Company Tax Return.
- From April 2028, Companies House will only accept accounts in iXBRL, filed through software.
- You don’t tag anything by hand. Filing software does it.
A4O Accounts prepares the CT600 from your books and files it with HMRC. See the CT600 software, or get started free.
How it works
An iXBRL file is an ordinary web page: open it in a browser and you see your balance sheet and profit and loss account laid out as usual. Behind each figure is a tag saying what it is, for example “turnover” or “cash at bank”, and which period and company it belongs to.
The tags come from published lists called taxonomies. Accounts use the FRC’s taxonomies, which follow the UK accounting standards (FRS 105 for micro-entities, FRS 102 for most other small companies). Tax computations use HMRC’s own computation taxonomy.
Who needs it
| Filing | iXBRL? |
|---|---|
| Company Tax Return (CT600) to HMRC | Yes. The tax computation sent with it must be in iXBRL, and for most companies the accounts must be too. |
| Annual accounts to Companies House | Accepted through software today. Required for all accounts from April 2028. |
Do you have to learn it?
No. Accounting and filing software applies the tags when it builds your accounts. What matters is that the software:
- uses the right taxonomy for your type of accounts,
- shows you a preview of the tagged accounts before you file, and
- produces files that HMRC and Companies House accept.
Common questions
Is iXBRL the same as a PDF?
No. A PDF is a picture of the page. iXBRL carries the data itself, which is why HMRC and Companies House can check figures automatically.
Do dormant companies need iXBRL?
HMRC usually doesn’t ask dormant companies for a Company Tax Return. At Companies House, dormant accounts are included in the move to software-only iXBRL filing from April 2028.
Can the same accounts go to HMRC and Companies House?
They start from the same figures, but the two versions can differ. For example, a small company might send fuller accounts to HMRC than it files on the public register. Good software prepares both from one set of books.
iXBRL in software
A4O Accounts produces your accounts and tax computation in iXBRL from your books, and shows you a preview of them as they’ll be filed. There’s nothing to tag by hand. See iXBRL accounts software, and what to send with a CT600 for how the tagged files fit into a return.
More in this series: all the CT600 guides.
File your accounts and Company Tax Return from one set of books
A4O Accounts prepares your accounts and CT600 from the same figures, tags them in iXBRL and files them with Companies House and HMRC. Free to get started, no card required.
Get started freeSources
- GOV.UK — Company Tax Returns: filing online
- GOV.UK — Companies House to bring in changes to accounts filing from April 2028
- GOV.UK — Using software to file your company’s information
This guide is general information, not tax or legal advice. Rules change, so check GOV.UK or ask an accountant about your company’s situation.