iXBRL Tagging: Complete UK Guide to Requirements, Software & Cost

What is iXBRL tagging?

iXBRL tagging is the process of wrapping individual figures in a company’s accounts with machine-readable labels from an XBRL taxonomy. Instead of submitting a plain PDF, UK companies send an Inline XBRL file that humans can read in a browser and machines can parse automatically at Companies House and HMRC.

Every balance-sheet item, turnover figure, and disclosure statement gets a unique tag such as core:TurnoverRevenue or core:FixedAssets. Those tags link to the FRC taxonomy used for UK GAAP accounts. Without them, the filing is not compliant.

What does iXBRL mean?

iXBRL stands for Inline eXtensible Business Reporting Language. It is the UK’s standard format for company accounts and tax computations. The format embeds XBRL tags directly inside an HTML document so the file displays like a normal web page while carrying structured data behind it.

The “i” is what makes iXBRL practical for UK filing: you get a readable document plus machine-readable data in a single file. That is why Companies House and HMRC have required it since 2011.

How iXBRL tagging works

Tagging follows a four-stage workflow regardless of whether you use software or work manually:

1. Prepare the source accounts — usually in Excel or your accounting package. The underlying numbers must be correct before you start.
2. Map each figure to a taxonomy tag — the software or tagging tool matches items like turnover, creditors, and equity to the correct FRC taxonomy element.
3. Generate the iXBRL file — the tool wraps the HTML presentation and inserts ix:nonFraction and ix:nonNumeric elements with the right context references and units.
4. Validate and file — run the file through a validator to catch missing tags, arithmetic mismatches, or wrong units before submission.

What information in accounts needs tagging?

Not every word needs a tag. The tagging target is the structured financial data. In a typical set of micro-entity or small-company accounts, the tagged items include:

• Entity information: company name, registration number, balance-sheet date, accounting period dates
• Director and approval details
• Balance-sheet figures: fixed assets, current assets, creditors (split by maturity), equity, net assets
• Profit-and-loss figures: turnover, profit or loss for the period
• Employee count (if required)
• Accounting standard applied and any statutory disclosures

iXBRL tagging vs ordinary financial statements

An ordinary PDF or printed set of accounts is human-readable only. A human can see the numbers, but Companies House and HMRC cannot extract them automatically.

Why UK companies need iXBRL tagging

Since 1 April 2011, HMRC has required iXBRL for Company Tax Returns. Companies House has moved to iXBRL as the standard filing format. From 1 April 2026, the free CATO tagging tool was retired, meaning all compliant filings now require commercial software or services. See our CATO shutdown guide for full details and alternatives.

iXBRL tagging ensures that:

• Your filing is accepted first time
• HMRC can process your tax return without manual data entry
• Companies House can validate your accounts against the correct taxonomy
• Regulatory data is consistent across filings

iXBRL tagging requirements

The core requirement is straightforward: every tagged monetary value must map to a valid element in the FRC taxonomy used for your accounting standard. For micro-entities filing under FRS 105, that means the FRS 102 entry-point taxonomy (micro-entities use the shared UK GAAP taxonomy with FRS 105 disclosures).

Practical requirements include:

• Complete balance-sheet tagging with the correct balance types (debit or credit)
• Correct units: monetary values use GBP, employee counts use PURE
• Proper context references for current year, prior year, and dimension contexts (creditors maturity, equity classes)
• A valid director approval statement and date of authorisation
• Compliance with the arithmetic validation rules in the relevant statutory instrument

iXBRL tagging requirements for HMRC

HMRC requires iXBRL for both accounts and computations filed with a CT600 Company Tax Return. The requirements are set out in HMRC’s accepted taxonomies guidance.

Key points:

• Accounts must be fully tagged using an accepted taxonomy entry point
• CT computations also require iXBRL tagging if filed electronically
• HMRC’s CT Online service closed on 31 March 2026; commercial software is now required
• Only US GAAP accounts may use a non-UK taxonomy; all other UK accounts must use UK GAAP taxonomies

iXBRL tagging for accounts

When we talk about iXBRL tagging of accounts, we mean applying tags to the statutory financial statements: the balance sheet, profit and loss account (where filed), and the required notes. The level of detail depends on the reporting regime:

• Micro-entity (FRS 105): minimal tagging — balance sheet, basic P&L, employee count, approval statement
• Small company (FRS 102 Section 1A): more tags, including abridged or full profit and loss
• Medium / large: full IFRS or FRS 102 tagging with extensive disclosures

How to tag accounts with iXBRL

The manual approach requires editing XML or HTML directly, inserting ix:nonFraction elements around monetary values and ix:nonNumeric elements around text. That is technically demanding and error-prone.

The practical approach is to use iXBRL tagging software. The typical workflow is:

1. Upload or enter your account figures into the software
2. Confirm the auto-suggested taxonomy tags for each line
3. Review the generated iXBRL preview
4. Run the built-in validator
5. Download the .xhtml file and upload to Companies House or your tax software

If your accounts start as PDFs, see our guide on how to convert PDF to iXBRL. If you use Excel, read about Excel to iXBRL conversion. For extracting data back out of an iXBRL file, see iXBRL to Excel.

Manual tagging vs iXBRL tagging software

What to look for in iXBRL tagging software

Not all tools are equal. When choosing software for iXBRL tagging, look for:

• Taxonomy coverage — supports the latest FRC taxonomy year relevant to your accounts
• Auto-tagging — suggests the right tag based on account descriptions
• Validation — catches arithmetic errors, missing tags, and unit issues before filing
• Filing integration — ability to submit directly to Companies House or export for tax software
• Support for your regime — FRS 105, FRS 102 Section 1A, or full IFRS as applicable

How much does iXBRL tagging cost?

iXBRL tagging cost varies depending on the route you take:

• Free / open-source tools (e.g., Arelle) — no licence cost but require technical skill and time
• One-off filing tools — typically £25–£60 per filing, suitable for occasional filers
• Subscription software — £50–£200/year, ideal for accountants and regular filers
• Professional services — from £150+ per set of accounts, best for complex or time-pressured situations

For a simple micro-entity filing, affordable software like QuickXBRL keeps the cost close to the one-off-filing tier while removing the manual work.

iXBRL tagging services vs software

iXBRL tagging services hand the work to a professional. You send your accounts and they return a compliant iXBRL file. This is useful if you lack time or technical confidence. The trade-off is cost and losing direct control of the tagging decisions.

iXBRL tagging software puts you in control. You enter the figures, confirm the tags, and file. For directors of small companies preparing their own accounts, software is usually the better balance of cost, speed, and accuracy.

Common iXBRL tagging mistakes

• Using the wrong balance type — crediting a debit balance or vice versa causes rejection
• Wrong units — employee count must use PURE, not GBP
• Missing contexts — every tagged value needs a valid context reference
• Arithmetic mismatches — net assets must equal equity; balance-sheet totals must add up
• Stale taxonomy — using an outdated entry point for the accounting period
• Untagged narrative disclosures — required text items such as the accounting-standard statement must be tagged

How to check/validate tagged accounts

Before filing, run your iXBRL through a validator. Checks typically cover:

• Schema conformance: does the file match the taxonomy schema?
• Unit correctness: are monetary values in GBP and counts in PURE?
• Arithmetic: do balance-sheet formulas hold?
• Completeness: are mandatory tags present?
• Dates: is the balance-sheet date consistent across contexts?

QuickXBRL validates during the tagging process so errors surface before you download the file.

iXBRL and Companies House / HMRC filing considerations

Filing iXBRL to Companies House and HMRC is not a single step. Companies House receives the accounts; HMRC receives the accounts and computations as part of the CT600 return. Both require valid iXBRL.

Key considerations:

• Use the correct taxonomy entry point for your accounting standard and period
• File before the deadline to avoid penalties (£150–£1,500+)
• Keep a copy of the submitted file for your records
• If you amend accounts, file a new iXBRL version with the updated tagging