iXBRL (inline eXtensible Business Reporting Language) is a web page version of the accounts in which each figure and many statements carry hidden tags. A person reads it as a normal document; HMRC’s and Companies House’s systems read the tags and know, for example, that a number is “Turnover” for the current year or “Average number of employees”.
Who already needs it
- HMRC: every company filing a CT600 online must submit its accounts and tax computation in iXBRL. This has applied for years, which is why most accounts software and accountants already produce tagged accounts.
- Companies House: software filing already uses iXBRL. From 1 April 2028, when web and paper accounts filing close, every accounts filing will need it.
How tags work
Each tag comes from a published taxonomy, the dictionary of permitted concepts. UK companies use the FRC taxonomies for FRS 102 and FRS 105 accounts. A tagged value carries:
| Element | Example |
|---|---|
| Concept | Debtors due within one year |
| Period | balance at 31 March |
| Unit | pounds sterling |
| Sign | positive or negative |
| Context | company, or a dimension such as “director A” |
Narrative items such as the name of the signing director, the approval date and the audit exemption statements are tagged too, which is how Companies House checks they are present.
Getting it right
Most errors come from mapping rather than technology:
- Wrong sign: a loss tagged as a positive profit.
- Wrong period: comparatives tagged as current year.
- Generic tags where a specific one exists, which makes the data less useful and can trigger HMRC validation warnings.
- Untagged mandatory items, such as the entity’s registered number or the accounts type.
Software that maps the trial balance to accounts headings and applies standard tags removes most of these risks. If the accounts are typed into a word processor and converted, a review of the tagging report (a list of each tagged value) is essential.
Choosing a route
- Accounts production software used by your accountant, which tags and files to both HMRC and Companies House.
- Accounting software with year-end filing, suitable for simple micro-entity and small company accounts.
- Tagging services that convert finished accounts into iXBRL, used when accounts are prepared outside dedicated software.
Whichever is used, keep the submitted iXBRL file. It is the definitive version of what was filed.
A short pre-filing check
- Company name and number match the register.
- Balance sheet totals in the tagged file match the signed accounts.
- The approval date and signing director are tagged.
- The accounts type (micro-entity, small, filleted, abridged) matches the statements on the balance sheet.
The wider timetable is in Companies House accounts filing changes from April 2028, and the filing steps in filing accounts with Companies House.