Definition
CATO (Company Accounts and Tax Online) was HMRC’s free online service for filing a company’s accounts and Company Tax Return (CT600) with HMRC. Small companies with straightforward tax affairs used it to file without buying software. It closed on 31 March 2026, so companies now need commercial software, or an agent such as an accountant, to file the CT600.
What replaced CATO
HMRC has not replaced CATO with another free service of its own. From 1 April 2026 it expects the CT600, the Corporation Tax computation and the accounts to be filed using commercial software, with the accounts and computation in iXBRL. A paper return is only accepted if the company has a reasonable excuse or is filing in Welsh.
Companies House filing is separate
Annual accounts still have to be filed with Companies House as a separate step, for example micro-entity accounts through WebFiling, or by software or paper. From 1 April 2028 Companies House will only accept accounts filed using software.
A director who used CATO for last year’s return now has two choices: subscribe to software that produces iXBRL accounts and computations, or hand the return to an accountant. SmartFiling’s guide to filing your own company accounts after CATO compares the options, and its CT600 filing service covers the HMRC side.
Related questions
- Can I file my own company accounts? Yes, but the HMRC filing now needs commercial software.
- What is iXBRL and do I need it? iXBRL is the tagged format HMRC requires for the accounts and computations filed with every CT600.
- How do I file a CT600 now HMRC's free filing service has closed? Through commercial software or an agent.
Related terms
-
CT600
The CT600 is the Company Tax Return a UK company files with HM Revenue and Customs (HMRC) for each accounting period.
Read definition -
iXBRL
iXBRL (inline eXtensible Business Reporting Language) is a digital format that adds machine-readable tags to each figure in a set of accounts while keeping the document…
Read definition -
WebFiling
WebFiling is Companies House's online service for filing company information without buying software.
Read definition -
Micro-entity accounts
Micro-entity accounts are the simplified annual accounts that a company qualifying as a micro-entity can prepare under the accounting standard FRS 105.
Read definition
