What Is iXBRL and Why Does Your CT600 Need It?

What Is iXBRL and Why Does Your CT600 Need It?

Every CT600 submission to HMRC must include accounts and tax computations in iXBRL format. But what is it, and why should you care?

iXBRL in Plain English

iXBRL stands for Inline eXtensible Business Reporting Language. It's a way of tagging financial data so computers can read it, while still looking like a normal document to humans.

Think of it like a Word document where every number has an invisible label:

• "This 50,000 is the turnover"
• "This 8,750 is the Corporation Tax payable"
• "This covers the period 1 April 2024 to 31 March 2025"

HMRC's computers read these tags to automatically cross-check your figures.

Why Does HMRC Require It?

Before iXBRL, HMRC staff had to manually read PDF accounts to check tax returns. With millions of companies filing, that's impossible.

iXBRL lets HMRC:

• Automatically validate your return against your accounts
• Cross-reference figures between different boxes
• Flag discrepancies for investigation
• Analyse trends across the entire company population

What Needs to Be in iXBRL?

Your CT600 submission includes three parts:

1. CT600 form — the XML return itself (not iXBRL, but XML)
2. Accounts — your balance sheet and P&L in iXBRL format
3. Tax computations — how you calculated your tax liability in iXBRL format

The accounts use the FRC (Financial Reporting Council) taxonomy — either FRS 105 for micro-entities or FRS 102 Section 1A for small companies.

The tax computations use HMRC's CT Comp taxonomy.

Can You Create iXBRL Yourself?

Technically yes, but practically no. iXBRL is complex:

• Documents must use the correct XBRL schema year
• Every tagged value needs the right element name, context, and unit
• Dimensional validation rules apply (some values can only appear in certain contexts)
• The file must pass schema validation and HMRC's business validation rules

This is why filing software exists.

How Taxpipe Handles iXBRL

Taxpipe generates all the iXBRL for you:

1. You enter your figures in a simple wizard
2. We generate FRS 105 micro-entity accounts in iXBRL
3. We generate tax computations in iXBRL
4. We generate the CT600 XML
5. Everything is bundled and submitted to HMRC

You never see or touch the iXBRL. You just answer questions.

Common iXBRL Errors

If you're using other software and getting iXBRL errors:

• Schema validation failed — wrong taxonomy year or missing required tags
• Dimensional validation error — a value is in the wrong context
• Period mismatch — dates in iXBRL don't match the CT600
• Missing mandatory elements — some tags are always required (e.g., company name, registration number)

The Bottom Line

iXBRL is the technical format HMRC requires. You don't need to understand it — you need software that generates it correctly. Taxpipe does this for £59.

File your CT600 with correct iXBRL — we handle all the technical formatting.