HMRC CATO is gone. What now?
On 31 March 2026, HMRC closed the Corporation Tax Online (CATO) service. This was the free browser-based tool that UK limited companies had used to file their CT600 returns for over a decade. No extension. No replacement from HMRC. Just a notice on GOV.UK and an expectation that every company will now use commercial software.
According to HMRC's own data, CATO handled around 1.5 million company tax return filings per year. That is a lot of directors who now need to find an alternative before their next filing deadline.
Why did HMRC close CATO?
HMRC stated that the closure is part of the move to Making Tax Digital (MTD) for corporation tax, which requires third-party commercial software to interact with the HMRC APIs. The free portal no longer fits the architecture. HMRC say commercial software provides a better experience. Whether that is true at £25 to £100+ per month is debatable.
What does this mean for your limited company?
If you used CATO to file your CT600 in previous years, you need to do one of the following for your next accounting period:
- Use HMRC-recognised commercial CT600 software to file yourself
- Appoint an accountant to file on your behalf
- Use an agent filing service
Accountants are the obvious fallback. But for a single-director company with straightforward finances, paying £800 to £2,500+ per year for an accountant is hard to justify when the actual filing is not complex.
What are the alternatives to CATO?
HMRC maintains a list of recognised software suppliers. The main options in 2026 are:
| Software | Price | Best for |
|---|---|---|
| NVC Comply | £25/month | Single-director limited companies |
| IRIS Elements | £40+/month | Accountants with multiple clients |
| FreeAgent | £19/month | Sole traders and small companies |
| Taxfiler | £12/month + filing fees | Price-sensitive micro-entities |
| Xero Tax | Included with Xero | Existing Xero bookkeeping users |
What does HMRC-recognised software actually do?
To file a CT600, software must be able to:
- Generate a CT600 form in the correct iXBRL format
- Generate statutory accounts in iXBRL (for the accounts part of the return)
- Submit both documents to HMRC via the API and receive a submission reference
iXBRL is a machine-readable financial reporting format that HMRC requires for all CT600 filings made through software. You cannot produce it in a spreadsheet; you need software that generates it automatically.
What does NVC Comply include?
NVC Comply was built specifically for single-director UK limited companies who want to file themselves without an accountant. It covers the full filing journey:
- Import bank transactions (CSV or direct bank connection)
- AI categorisation of expenses using UK tax rules
- CT600 computation: marginal relief, capital allowances, director loans
- iXBRL accounts for micro-entity (FRS 105) and small companies (FRS 102)
- Direct filing to HMRC and Companies House
The first accounting period is free. No credit card required to start.
If you were using CATO and your next filing deadline is approaching, you can import your transactions and generate your CT600 with NVC Comply. First period at no cost.
Start filing freeDo I need to tell HMRC I'm switching software?
No. You do not need to notify HMRC that you are changing from CATO to commercial software. The submission process is the same. HMRC will receive your CT600 and accounts via the API and you will receive a submission reference number as confirmation.
When is my CT600 due?
CT600 filing deadlines are set at 12 months after the end of your accounting period. So if your company year end is 31 March 2026, your filing deadline is 31 March 2027. Your corporation tax payment is due 9 months and 1 day after the end of your accounting period: 1 January 2027 in that example.
Late filing penalties start at £100 per return, rising to £200 after 3 months, and to tax-geared penalties after 6 months. It is worth getting software in place well before the deadline, not the day before.