CT600 software: what to check before you choose
A limited company files its Company Tax Return online, with commercial software. Here is what that software does, where HMRC's list of suppliers is, and the questions worth asking first.
This guide describes how the rules work and how this service treats them. It is not tax or legal advice, and no accountant has reviewed it yet. Check your own company's dates and figures on GOV.UK, or with an accountant, before relying on them.
Why a company needs software
A Company Tax Return is filed online with commercial software, by the company or by an accountant acting as its appointed agent. A paper CT600 is only for a company with a reasonable excuse for not filing online, or one filing in Welsh.
HMRC's own online service for filing the accounts and the return closed on 31 March 2026, so a company that used it before needs another way to file.
What the software does
- It fills in the CT600 and any supplementary pages the return needs, and submits the return online.
- It takes the accounts and the computations as iXBRL, the format HMRC reads. HMRC says suppliers also provide services to produce iXBRL accounts and computations.
- Some of it files the return and the annual accounts together.
Suppliers differ in how much of this they do themselves, which is why it is worth asking rather than assuming.
HMRC's list of suppliers
HMRC publishes the list of commercial software suppliers for Corporation Tax on GOV.UK, and updates it often, with suppliers added and removed through the year. Use the list itself, not an older article, to see what is on it today.
The list has separate sections for software that produces and submits the CT600 and for the different ways of getting iXBRL accounts and computations: software with the tagging built in, a managed tagging service and conversion software.
Questions to ask before you choose
Is it on HMRC's list?
Check the supplier on the list on GOV.UK, in the section for the job you need done.
Does it cover your return?
Ask about the supplementary pages your company needs, such as loans to participators, and about a company that files more than one return for the same accounts.
Does it take accounts and computations made elsewhere?
Some services accept iXBRL files that were prepared in other software. Others only prepare their own. Ask which.
Can you key the boxes yourself?
Ask whether it lets you key the CT600 boxes, or only takes files.
Will it also file the accounts at Companies House?
From 1 April 2028 every company must file its accounts with Companies House using commercial software, and not all software supports the iXBRL tagging those need. Ask whether it will.
Who makes the declaration?
The return ends with a declaration giving the name, date and status of the person making it. Decide who that is, you or your accountant, and make sure they can read the whole return first.
Would your accountant rather file it?
A company can get an accountant to prepare and file its return, and can authorise an agent, such as an accountant, to manage its tax affairs with HMRC.
Where this service fits
This service does not file anything. An owner approves the filing pack, and you, or your accountant, file the accounts and the return, with a step-by-step guide to follow. The filing by hand page has the detail.
Before you pay a supplier to file a pack, ask whether it accepts iXBRL accounts and computations made elsewhere, or lets you key the CT600 boxes yourself. The files in a pack are only useful to one that says yes to at least one.
A qualified accountant has not reviewed the calculations. Treat the output as a working draft for you or your accountant to check.
Sources
The facts in this guide come from these pages, read on . Rules, dates and figures change, so check the page itself before you rely on one.
Keep reading
- The Company Tax Return (CT600) explained
What a UK limited company's Company Tax Return (CT600) is, what goes in it, how its dates work, and what happens when it is late or wrong.
- Filing company accounts: Companies House and HMRC
Where a UK limited company's annual accounts go, who must approve them, which dates apply, and what changes in April 2028 when accounts need software.
- Filing deadlines for a UK limited company
When a private limited company files accounts, pays Corporation Tax, files its CT600 and sends its confirmation statement, and how the dates work.
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