CATO closed on 31 March 2026. These were the rules it ran on, and they still matter if you are working out whether your company was a CATO user.
CATO closed on 31 March 2026. HMRC’s free Company Accounts and Tax Online service is no longer available, and Corporation Tax returns must now be filed using commercial software. This page explains the eligibility rules the service ran on. For what to do now, see HMRC’s free CT600 filing service has closed.
The short version
- CATO was for small companies filing for themselves, with no audit and straightforward tax affairs.
- The size test was the pre-2025 micro-entity test: turnover up to £632,000, balance sheet total up to £316,000, 10 employees or fewer.
- Agents were excluded. An accountant could not file through CATO on a client’s behalf.
- Eleven exclusions applied regardless of size, covering audited accounts, groups, liquidation and several company types.
- It closed on 31 March 2026 and was not replaced.
Who could use CATO
In an ideal world it would cost a company nothing to file its annual tax return with HMRC and its accounts with Companies House. For a narrow band of small companies, for about a decade, that was close to true. HMRC’s Company Accounts and Tax Online service, CATO, let them do both for free.
It was never open to everyone, and the rules that decided who could use it are worth knowing now, because they are how you tell whether your own company was one of them.
Who qualified
CATO was a free service and HMRC kept it narrow. A company could use it if it was a micro-entity or a small company, was exempt from filing audited accounts, and had straightforward tax affairs.
The size test was the micro-entity test as it stood at the time: turnover of no more than £632,000, a balance sheet total of no more than £316,000, and 10 employees or fewer. Charities had a separate turnover ceiling of £6.5 million.
Those figures matter more now than they did then. The micro-entity thresholds rose on 6 April 2025 to £1 million turnover and a £500,000 balance sheet total, so a company can be a micro-entity today and still have been too large for CATO. If you are testing yourself, test against £632,000.
Who never qualified
A company could not use CATO if any one of the following applied:
- its accounts required an audit, or had been audited
- it was part of a group
- it was not registered in the UK
- it was in liquidation or receivership
- it had to pay its Corporation Tax in instalments
- its accounting period for the Corporation Tax return was covered by more than one set of statutory accounts
- it needed to claim repayment of a loan to a participator, such as a director’s loan, more than nine months after the end of the accounting period
- it was an insurance company, other than an independent insurance broker
- it was an investment company
- it was a credit union
- it was a commercial property management company
Agents could not use it at all
This is the part most often missed. CATO was designed for unrepresented companies, filing for themselves with their own filing credentials. HMRC was explicit with the profession at the time that the service was a basic one, not intended to meet the professional needs of agents, and it was built so that it could be restricted that way.
So an accountant or accounting firm could not file through CATO on a client’s behalf. Any practice that lost something when CATO closed lost it indirectly, through clients who had been filing for themselves.
What CATO let you do
Within those limits it did a lot for a free tool. A company could file its Corporation Tax return with HMRC, file its annual accounts with Companies House, or do both at once from one set of figures. That last part is what most former users miss, because it is the step that disappears when the two filings are separated.
Every return filed through it had to be a complete electronic submission: the CT600 itself, the Corporation Tax computation, and the statutory accounts, all in iXBRL where the format required it. CATO handled the tagging in the background, which is one reason it suited companies with no accounting background.
How to tell whether you were a CATO user
- You filed your own Corporation Tax return, without an accountant doing it for you.
- You signed in with your company’s own Government Gateway credentials rather than through an agent.
- Your turnover was £632,000 or less in the years you filed.
- Your accounts were unaudited.
- None of the exclusions above applied to your company.
- You paid nothing to file.
If all six are true, you were filing through CATO.
What replaced it
Nothing directly. HMRC did not build a successor and has said it does not intend to, on the basis that it should not be competing with commercial software suppliers.
Since 1 April 2026 every Corporation Tax return has had to be filed through commercial software, with paper accepted only where there is a reasonable excuse or the return is in Welsh. HMRC publishes a list of recognised suppliers.
Companies House filing was not affected. Its own WebFiling service is still open and still free. It closes for accounts on 31 March 2028, and from 1 April 2028 accounts filing moves to commercial software in iXBRL format for every UK company.
Keeping the two apart
CATO handled both filings, which is why its closure is often read as having ended both. It did not. HMRC and Companies House are separate filings, with separate deadlines, separate penalty regimes and, now, separate timelines. Only the HMRC half changed in 2026.
Frequently Asked Questions
What did CATO stand for?
Company Accounts and Tax Online. It was HMRC’s free joint filing service, run with Companies House, and it closed on 31 March 2026.
Could I file only my accounts through CATO, without the tax return?
Yes. A company could file its Corporation Tax return with HMRC, its accounts with Companies House, or both together. The two filings were separate even inside CATO.
Why was turnover capped at £632,000?
That was the micro-entity turnover threshold at the time. It rose to £1 million for financial years beginning on or after 6 April 2025, but CATO’s eligibility was never updated to match before the service closed.
Could my accountant use CATO for me?
No. HMRC built it for companies filing for themselves and did not open it to agents. An accountant filing on a client’s behalf had to use commercial software.
I was eligible but never used it. Does that matter now?
Not for your filing obligations, which are the same either way. It may matter for pricing, as some software providers offer concessions to companies that previously filed through CATO.
Can I still access my old CATO filings?
Not through the service. Request Corporation Tax returns from HMRC and accounts from Companies House directly.
If you were a CATO user and need to file now, our guide to what to do since HMRC’s free service closed sets out the route, the deadlines and the penalties.
About DataTracks
DataTracks is a software and services provider for regulatory reporting, working with businesses in more than 25 countries since 2005.
DTracks Limited is recognised by HMRC as an iXBRL Managed Tagging Service provider and as a commercial software supplier supporting Pillar 2 returns, and by Companies House as an authorised software provider for filing company accounts.
