SimpleReturns

What is iXBRL? (tagged accounts, in plain English)

Updated 27 June 2026
The short answer

iXBRL is a digital format that labels every figure in your company accounts and tax workings so HMRC's computers can read them straight away. When you file your tax return online, the accounts and the workings have to be in this format, not a plain PDF and not on paper. You never tag anything by hand, the filing software does it for you.

So what is iXBRL, really?

Think of your company accounts as a page of numbers. To a person, "£40,000" sitting next to the word "turnover" makes sense. To a computer, it's just text on a page. iXBRL fixes that. It puts a hidden label on each figure that tells the computer what it is: this number is your turnover, this one is your profit, this one is the tax you owe.

So iXBRL is a digital format HMRC's computers can read by themselves, with every important figure labelled. The page still looks normal to you. The labels sit underneath, where only a computer looks.

You don't need to understand any of the labelling. It happens behind the scenes.

Do I have to use it?

Yes. When you file your company's tax return online, your accounts and your tax workings (the bit that shows how your profit turns into your tax bill) both have to be in this format. That is the rule for almost every small company.

You can't get round it by sending a plain PDF or printing it and posting it. For almost every small company, a return like that doesn't count as filed, so you'd be treated as if you hadn't filed at all.

This has been the rule for a long time, so it isn't new or optional. It's simply how Corporation Tax returns go to HMRC now.

Do I have to do the tagging myself?

No. This is the part people worry about for no reason. You do not sit there labelling figures one by one. The filing software does the tagging for you, automatically, the moment your return is built.

Your job is to get your figures right. The format is the software's job.

What does a tax return actually contain, then?

When you file online, three things go to HMRC together:

  • The CT600. This is the Corporation Tax return form itself, your company's details and the tax due.
  • Your accounts. The summary of the money that came in and went out over the year, in iXBRL.
  • Your tax workings. The short bit that shows how your profit becomes your tax bill, also in iXBRL.

The CT600 ties it together, and the two iXBRL parts are the ones that have to carry the hidden labels.

A plain example

Say your company made £40,000 of profit for the year. In your accounts, that figure appears as text on a page. On its own, HMRC's computer can't tell £40,000 of profit from £40,000 of anything else.

For example

With iXBRL, that same £40,000 gets a hidden tag that says "this is the profit". HMRC's system reads the tag, picks up the £40,000 as your profit, and lines it up with the rest of your return without a person retyping it. Same number on the page, just readable by machine. You did nothing extra, the software added the tag when it built your return.

Common questions

What does iXBRL stand for, in plain words?

It's the name of a digital format that labels the figures in your accounts so a computer can read them. You don't need the full name to file, you just need your accounts and workings to be in it, and the software handles that.

Can I just send HMRC a PDF of my accounts instead?

No. For almost every small company, a plain PDF or a paper copy isn't accepted for the accounts or the tax workings, and the return won't count as filed. They have to be in the tagged format.

Do I have to learn how to tag the figures?

No. The filing software does the tagging for you automatically. You never label anything by hand.

Is iXBRL the same as my CT600?

No. The CT600 is the return form. iXBRL is the format your accounts and tax workings have to be in when they go to HMRC alongside that form.

Why does HMRC even want it?

So their computers can read your figures straight away instead of a person retyping them. It makes returns quicker to process and easier to check.

Ready to skip the jargon?

You don't need to know what iXBRL is to file. We build your accounts and your tax workings in the format HMRC needs, add all the hidden labels for you, and show you every figure in plain English before anything is sent, for £99, once, no subscription.

Start your return →

Or, if your company is more complex, like a group, an accountant may be the better fit, and that's an honest call to make.

General guidance, not advice. This guide explains how the rules generally work for small UK limited companies. It isn't tax advice for your specific situation, if you're unsure, check with us or an accountant.