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Dormant company iXBRL accounts explained

By Max Szolcek, founder of Dormant Return. Last updated 21 August 2026

A Company Tax Return is not just the CT600 form. HMRC requires the company's accounts to be delivered inside the return, tagged in a machine-readable format called iXBRL. This is true even when the company is dormant and every figure is zero, and it is the main reason a dormant return cannot simply be typed into a web form and posted off.

What iXBRL actually is

iXBRL stands for Inline eXtensible Business Reporting Language. An iXBRL document is an ordinary human-readable web page (the accounts as you would print them) with invisible tags wrapped around each fact: this number is Called-up share capital, this date is the balance sheet date, this text is the directors' declaration. People read the page; HMRC's computers read the tags.

The tags come from published dictionaries called taxonomies, maintained by the Financial Reporting Council. Accounts must be tagged against the right taxonomy for the accounting standard they follow (for a small dormant company that is typically the FRS 102 or micro-entity framework), and HMRC validates the tagging on submission. Wrongly tagged accounts are rejected in the same breath as a wrong UTR.

Why a PDF is not enough

Before April 2011 companies could attach accounts to their return as a PDF. HMRC ended that: since then, accounts filed with a CT600 must be iXBRL so that HMRC's risk systems can read the figures automatically. There is no dormant-company exemption from the format. A return arriving without valid iXBRL accounts (where accounts are required) is rejected outright.

What dormant accounts contain

For a typical dormant company limited by shares, the accounts inside the return are short: a balance sheet (often all zeroes, or just the share capital), the statutory declarations that the company was dormant and entitled to the audit exemption, the accounting standards applied, and the director's approval with a date and name. The challenge is not writing them; it is producing them as valid iXBRL, with every required tag present and dimensionally correct, in a form HMRC's gateway accepts.

Doing that by hand is genuinely technical (taxonomies, contexts, dimensions, transformation rules), which is why the practical answer is software that generates the tagged accounts from a handful of inputs. Dormant Return generates the iXBRL dormant accounts automatically from your company's details, shows you the exact document before anything is filed, and validates it the way HMRC will.

Is this the same as Companies House dormant accounts?

No. Companies House has its own separate accounts filing (dormant companies can file simple dormant accounts there for free), with its own format rules. The iXBRL accounts described here live inside the HMRC Company Tax Return. Filing one does not file the other; the split is explained in dormant for Companies House vs dormant for Corporation Tax.

Skip the tagging homework. Dormant Return prepares the CT600 and the iXBRL dormant accounts together and files them to HMRC in about five minutes, for £5. You see the accounts exactly as HMRC receives them.

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