CT600 software: what to look for
Since 1 April 2026, Company Tax Returns go to HMRC through commercial software. Products differ in where the figures come from, which parts of the return they produce and which supplementary pages they support, so it’s worth checking a few things before you start a return in one.
- GOV.UK lists commercial software for Company Tax Returns. HMRC accepts returns from the products on it, which isn’t the same as recommending them.
- Check the software produces the whole return: the CT600, the accounts and the computation, in iXBRL.
- Check it supports any supplementary pages you need.
- Think about where the figures come from, and whether it files your Companies House accounts too.
A4O Accounts prepares the CT600 from your books and files it with HMRC. See the CT600 software, or get started free.
Start with GOV.UK’s list
GOV.UK publishes a list of commercial software suppliers and products you can use to file a Company Tax Return and any supplementary pages online. It says HMRC accepts returns filed using any of the products shown. That tells you a product can file. It doesn’t tell you whether it suits your company, so the questions below still matter.
Seven things to check
1. Does it produce the whole return? A return is the CT600, the company’s accounts and a tax computation. Some products fill in the CT600 and expect you to bring the accounts and computation, already in iXBRL, from somewhere else. See what to send with a CT600.
2. Does it produce the iXBRL? The computation must be in iXBRL, and for most companies the accounts must be too. If the software doesn’t produce them, you need a second tool that does.
3. Does it support the supplementary pages you need? If a director owes the company money you’ll need CT600A. If you claim R&D relief you’ll need CT600L. GOV.UK’s list shows the pages each product supports. See the supplementary pages explained.
4. Where do the figures come from? Some products start with an empty return and you type in final figures from accounts prepared elsewhere. Others build the accounts and the return from your bookkeeping. Typing figures across is quicker to start with, and it’s where mistakes get in.
5. Does it file your Companies House accounts too? They’re a separate filing with an earlier deadline, and from April 2028 Companies House will require them to be filed through software as well. One product for both means one set of figures. See the April 2028 change.
6. Can you see what will be sent? Look for a box-by-box view of the CT600, a preview of the tagged accounts and computation, and a way to send a test submission before filing for real.
7. What happens after you file? You may need to amend the return, and next year’s return needs this year’s losses and capital allowance pools. Check the software keeps what was filed and carries the figures forward.
Then the practical questions: what it costs per return or per year, whether you pay before you can file, and whether you can get your data out.
Which kind of product suits which company
| Kind of product | How it works | Suited to |
|---|---|---|
| Filing tool | You enter final figures into forms, and it produces and files the return | A company with simple affairs and accounts already prepared, or very few transactions |
| Accounts production and tax suite | Imports a trial balance, then produces accounts, computation and return, usually across many clients | Accountancy practices, and companies with complex returns or unusual supplementary pages |
| Bookkeeping-to-filing product | Keeps the books, and builds the accounts and return from them | Companies and practices that want the books, accounts and return in one place |
None of these is the right answer for everyone. A dormant or near-dormant company doesn’t need a bookkeeping system, and a group with consolidated accounts needs more than most small-company products offer.
Where A4O Accounts fits
A4O Accounts is the third kind. You keep the company’s books in it, and the statutory accounts, the tax computation and the CT600 are built from them and tagged in iXBRL. It files the return with HMRC and the accounts with Companies House, as separate filings, and you can send a test submission first. It’s free to get started, including filing.
It’s suited to UK limited companies filing micro-entity, small or full accounts, and to accountants and bookkeepers looking after them.
It’s not suited to every return. It supports CT600A and CT600L but no other supplementary pages. It doesn’t do group or consolidated accounts. It has no HMRC agent sign-in: you enter the company’s Government Gateway user ID and password when you file. And there’s no form to type final figures into, so the books need to be in it.
See CT600 software for the detail, how it compares with other products, or how to move from HMRC’s free service.
More in this series: all the CT600 guides.
File your accounts and Company Tax Return from one set of books
A4O Accounts prepares your accounts and CT600 from the same figures, tags them in iXBRL and files them with Companies House and HMRC. Free to get started, no card required.
Get started freeSources
- GOV.UK — Filing your Company Tax Return online (commercial software suppliers)
- GOV.UK — Filing company accounts and tax returns if you previously used the HMRC online service
- GOV.UK — Company Tax Returns
- GOV.UK — Companies House to bring in changes to accounts filing from April 2028
This guide is general information, not tax or legal advice. Rules change, so check GOV.UK or ask an accountant about your company’s situation.