What Is iXBRL? Explained Simply for Company Directors
When filing your CT600, HMRC requires your accounts and tax computations in "iXBRL format". If you're not an accountant, that probably sounds like jargon. Here's what it actually means and why you should care.
iXBRL in Plain English
iXBRL stands for inline eXtensible Business Reporting Language.
In practice, it's a way of creating financial documents that are:
- Human-readable — they look like normal accounts (HTML/web page)
- Machine-readable — each number has an invisible tag that tells computers what it represents
Think of it like a PDF that's also a spreadsheet. You can read it normally, but HMRC's computers can automatically extract and process every figure.
Why Does HMRC Require iXBRL?
Before iXBRL, HMRC staff had to manually read and process paper accounts. With iXBRL:
- Automated processing — HMRC's systems can instantly check figures
- Cross-referencing — numbers in your CT600 are automatically matched against your accounts
- Faster refunds — less manual handling means quicker processing
- Better risk analysis — HMRC can automatically flag unusual figures
What Needs to Be in iXBRL Format?
When filing your CT600, two attachments must be in iXBRL:
1. Company Accounts
Your balance sheet, profit and loss account, and notes — the same financial statements you file at Companies House.
2. Tax Computations
The calculation that bridges your accounting profit to your taxable profit, showing adjustments like:
- Disallowable expenses
- Capital allowances
- Other tax adjustments
- The corporation tax calculation itself
Taxonomy Standards
iXBRL uses standardised "taxonomies" — essentially dictionaries of tags. HMRC recognises:
| Taxonomy | Used For | Company Size |
|---|---|---|
| FRS 105 | Micro-entity accounts | Turnover ≤ £632K |
| FRS 102 Section 1A | Small company accounts | Turnover ≤ £10.2M |
| Full FRS 102 | Medium/large accounts | Larger companies |
| CT Computations | Tax computations | All companies |
Most limited companies file under FRS 105 (micro-entity) or FRS 102 Section 1A (small company).
How to Create iXBRL Files
Option 1: Filing Software (Easiest)
CT600 filing software like Taxpipe generates iXBRL automatically. You enter your financial data through a guided wizard, and the software produces correctly tagged accounts and computations.
This is how most small companies do it. No technical knowledge required.
Option 2: Accounting Software
Some accounting packages (Xero, Sage, FreeAgent) can export iXBRL-tagged accounts. You may still need separate software for the tax computation.
Option 3: Specialist Tagging Tools
For complex accounts, accountants use tagging tools to manually apply iXBRL tags to financial statements. This is expensive and usually only needed for larger companies.
Option 4: Accountant
Your accountant handles everything. This typically costs £300-800 for a basic CT600 with iXBRL accounts.
Common iXBRL Errors
Wrong Taxonomy Version
Using an outdated taxonomy causes HMRC rejection. Your software should use the latest version automatically.
Missing Mandatory Tags
Certain elements must always be present:
- Company name and registration number
- Balance sheet date
- Start and end of reporting period
- Director approval statement
Validation Errors
HMRC's system checks that tagged values are consistent. For example:
- Assets must equal liabilities plus equity
- Period dates must match your CT600
- Monetary values must be in the correct format
Do I Need to Understand iXBRL?
No. If you use filing software, iXBRL is handled entirely behind the scenes. You enter your figures, the software generates valid iXBRL, and HMRC receives correctly formatted files.
Think of it like PDF — you don't need to understand how PDFs work to create and send one. The software handles the technical format.
What About Companies House?
Companies House also requires iXBRL accounts. The good news: the same iXBRL file can be submitted to both HMRC and Companies House, though the level of detail may differ:
- HMRC: Full accounts (all figures needed for tax purposes)
- Companies House: Can be abbreviated/abridged (less detail on the public record)
Key Takeaways
- iXBRL = documents that humans and computers can both read
- HMRC requires it for CT600 accounts and tax computations
- Filing software generates it automatically — you don't need to understand the technical details
- Most small companies use FRS 105 or FRS 102 Section 1A taxonomy
- Errors are caught by software validation before submission
File iXBRL-Compliant Accounts Automatically
Taxpipe generates HMRC-compliant iXBRL accounts and tax computations as part of your CT600 filing. No tagging, no technical knowledge, no fuss.
File your CT600 → — £59, iXBRL included, validated before submission.