iXBRL accounts checker

Can I use this checker in an AI assistant?

Not this checker: it needs a file upload, so it only works on this page. Taxley's other free calculators, such as Corporation Tax, deadlines, late filing penalties and director's loan tax, work inside Claude, ChatGPT or your own code through a free MCP server, with no key and no sign-up.

What is an iXBRL file?

An iXBRL file is a web page version of your accounts or tax computations with hidden tags on every figure and key fact, such as turnover, profit and the company number. HMRC requires company accounts and computations in iXBRL with every Company Tax Return, so its systems can read the figures automatically.

The tags come from a published list called a taxonomy. Accounts use the Financial Reporting Council's taxonomy for FRS 102 or FRS 105, and tax computations use HMRC's computations taxonomy. See HMRC's XBRL guide for UK businesses.

What does the iXBRL checker look for?

The checker first makes sure the file is well formed: valid XHTML, a schema reference, contexts, units and tagged numbers that point to them. It then validates every tag against the taxonomy the file names and lists each problem in plain English, with the technical error code beside it for your software supplier.

It also reads back the key facts it found, such as the company name and number and the period dates, so you can check the file describes the right company and year.

Which taxonomies can the checker validate?

The full taxonomy check covers the FRC 2025 taxonomy used for FRS 102 and FRS 105 accounts and HMRC's 2024 Corporation Tax computations taxonomy. Files built on other versions still get every structural check, but the result says clearly that the taxonomy check could not run, rather than calling the file valid or broken.

Is my file kept or shared?

No. Your file is saved to a temporary location only for the few seconds it takes to check, and deleted as soon as the check finishes, whatever the result. We do not store the file, log its contents or share it. The report is shown on the page and is not saved.

What should I do if the checker finds errors?

Most iXBRL errors come from the software that produced the file, so send the error list to your software supplier or whoever prepared the accounts. Common fixes are a missing company number tag, a figure with no unit, or a context whose dates do not match the accounting period. Then check the corrected file again.

If you are filing your own Company Tax Return, Taxley produces the iXBRL accounts and computations for you and checks them before anything is sent to HMRC.

Which rules does this calculator follow?

Every figure comes from the rules HMRC and Companies House publish on GOV.UK, and from the legislation behind them. The links below go to the pages we checked when we last reviewed this calculator, so you can read each rule in full and check that it applies to your company.

• HMRC: XBRL guide for UK businesses
• HMRC: taxonomies accepted by HMRC
• GOV.UK: Company Tax Returns

Frequently asked questions

Is the iXBRL checker free?

Yes. The checker is free and you do not need an account. You can check up to four files every ten minutes. Each file is checked on its own and deleted straight afterwards, so you can re-upload a corrected version as often as you need while you fix any problems it finds.

Does a pass mean HMRC will accept my accounts?

Not on its own. A pass means the file is well formed and its tags are valid for the taxonomy it names. HMRC also applies its own business rules to the return as a whole, such as matching figures between the CT600, the computations and the accounts, which this checker does not test.

Which files can I upload?

Upload one iXBRL file with the .html, .xhtml or .htm extension, up to 2 MB. That can be your company accounts or your Corporation Tax computations. PDFs, Word documents and spreadsheets are not iXBRL, so the checker turns them away with a short message saying why.

Why does my file say it was not fully checked?

The full taxonomy check needs the taxonomy your file names. The checker holds the FRC 2025 accounts taxonomy and HMRC's 2024 computations taxonomy. A file built on another version still gets the structural checks, but the result says the taxonomy check could not run instead of guessing.

Do you keep or look at my file?

No. The file is saved to a temporary location only while it is checked, then deleted. We do not store it, log its contents or use it for anything else. Only the list of problems is shown back to you, on the page, and it is not saved either.

Related free tools

• Corporation Tax calculator: Estimates the Corporation Tax a UK limited company pays on its taxable profits for one accounting period of up to 12 months. Applies the small profits rate, the main rate and marginal relief, with associated companies, short periods and periods that straddle 1 April. A close investment-holding company pays the main rate on all its profits. Returns the tax, the effective rate and the payment and filing dates.
• Corporation Tax deadline calculator: Works out a UK private limited company's Corporation Tax payment date, CT600 filing deadline and Companies House accounts deadline from its accounting period. Accounts longer than 12 months are split into two Corporation Tax periods, each with its own payment date.
• Corporation Tax late filing penalty and interest calculator: Works out HMRC's penalties for filing a UK company's Company Tax Return (CT600) late — the flat £200/£400 penalties, doubled for filing deadlines from 1 April 2026, and the 10% or 20% tax-geared penalty — plus late payment interest on the Corporation Tax at HMRC's published rates.
• All free Corporation Tax tools

Last reviewed 29 September 2026. This calculator gives general guidance, not tax advice.