CATO has closed — what are your options now?

By Ben Davies · Updated 5 October 2026

HMRC shut down its free filing service, CATO, on 31 March 2026. If you relied on CATO to file nil CT600 returns (Company Tax Returns showing no tax to pay) for a dormant company, the return now has to go through commercial software.

What was CATO?

CATO — Company Accounts and Tax Online, officially "File your accounts and Company Tax Return" — was HMRC's free web-based service for filing a company's accounts and its CT600 Corporation Tax return together. It was basic and not always intuitive, but it cost nothing. For directors of dormant companies filing nil returns, CATO was the obvious choice.

HMRC closed it on 31 March 2026 as part of a broader move to shift Corporation Tax filing to commercial third-party software. A CT600 now has to go through commercial software; paper is only for a reasonable excuse or a return in Welsh.

Where to file now

1. DormantFile — built for dormant companies

We built DormantFile in direct response to CATO closing. It files a dormant company's tax return and its accounts:

• Nil CT600 submitted to HMRC via their GovTalk API
• Dormant accounts submitted to Companies House via their software filing API

Around those two filings it reminds you of the confirmation statement (which you file yourself) and keeps an eye on your directors' identity checks and the public register.

Pricing starts at Basic £19/year for one company, £39/year for up to 10 companies on the Multiple plan, or £49/year for up to 100 companies on the Agent plan. See our pricing page for full details. No accounting knowledge needed, no features you don't need.

DormantFile is for dormant and non-trading companies only. If your company is trading, or its tax return would show a profit or tax to pay, you need accounting software or a professional.

2. General accounting software

Full-featured accounting packages can file CT600 returns. They are designed for trading companies — invoicing, payroll, bank feeds, VAT and more — and pricing typically starts at £100+/year. For a dormant company with zero transactions, that is significant overkill, and the software assumes you have actual accounting to do.

3. An accountant

An accountant can file your CT600 on your behalf. For a nil return, expect to pay £80–£150 per company per year — an expensive way to file a return with nothing on it. Not sure whether your company is dormant? Our free dormancy checker works it out.

What about annual accounts?

CATO filed the accounts as well as the tax return, so if you used it, your annual accounts need a new route too. DormantFile files both from one place — the dormant accounts to Companies House, including for a company that traded before and still carries figures from those years, and the nil CT600 to HMRC. We cover the accounts in our guide on how to file dormant company accounts; see how it works.

What if you don't file?

If HMRC has sent the company a notice to deliver a Company Tax Return, you are legally required to file a CT600 return for the period it names. Not filing results in:

• A £200 penalty if one day late
• Another £200 if three months late — though both are £100 where the return fell due before 1 April 2026, which catches a lot of CATO's last users
• HMRC estimates your tax liability and charges 10% of the unpaid tax at six months
• A further 10% at twelve months

Companies House has its own separate late filing penalties for accounts.

Key points

• CATO, HMRC's free filing service, closed on 31 March 2026. A CT600 now has to go through commercial software.
• DormantFile is purpose-built for dormant companies, from £19/year, covering both CT600 and Companies House accounts.
• General accounting software starts at £100+/year and is overkill for nil returns.
• An accountant costs £80–£150 per company per year for a nil return.
• CATO filed accounts too, so your annual accounts for Companies House need a new route as well.