HMRC CT600 Online Service Closing: What You Need to Know
HMRC's free Company Accounts and Tax Online (CATO) service will permanently close on 31 March 2026. From 1 April 2026, all UK limited companies must use commercial software to file their Corporation Tax returns.
If you've been using HMRC's free online service to file your CT600, you need to act now to prepare for this change.
What Is Closing?
Since 2011, HMRC has offered a free online service called Company Accounts and Tax Online (CATO). This joint filing service allowed small companies to:
- File their annual accounts
- Submit their Corporation Tax return (CT600)
- Forward accounts to Companies House automatically
Why Is HMRC Closing the Service?
HMRC has cited several reasons for closing CATO:
- Outdated technology — The system no longer meets current digital standards
- Legislative changes — The Economic Crime and Corporate Transparency Act (ECCTA) 2023 requires enhanced data validation that CATO cannot support
- Funding constraints — Public sector budget cuts have made the service unsustainable
- Improved alternatives — Modern commercial software offers better functionality, including automated error checking
Key Dates to Remember
| Date | What Happens |
|---|---|
| Now until 31 March 2026 | CATO remains available — use this time to prepare |
| 31 March 2026 | Last day to file using HMRC's free online service |
| 1 April 2026 | You must use commercial software for all CT600 filings |
| 1 April 2027 | Companies House WebFiling also closes for accounts |
What You Need to Do
1. Download Your Filing History
Do this immediately. After 31 March 2026, you will lose access to your previous returns filed through CATO.
HMRC recommends downloading at least the last three years of filings:
- CT600 returns
- Computations
- Submitted accounts
2. Choose Commercial Software
You need software that is approved by HMRC to submit CT600 returns electronically. When choosing, consider:
- Cost — Prices range from free (like TinyTax) to several hundred pounds per year
- iXBRL capability — Must generate iXBRL-tagged accounts
- Ease of use — Important if you're filing yourself rather than using an accountant
- Trial balance import — Saves time if you use accounting software like Xero or QuickBooks
3. Make the Switch Early
Don't wait until March 2026. Benefits of switching now:
- Learn the new software without deadline pressure
- Resolve any issues before the old service closes
- Take advantage of better error checking in modern software
- No need to notify HMRC when you switch
Who Is Exempt?
Some organisations may be eligible to continue filing paper CT600 returns after March 2026:
- Charities registered with HMRC
- Community amateur sports clubs (CASCs)
- Dormant companies (in some circumstances)
What About Companies House?
Companies House is making separate changes. From 1 April 2027, you will no longer be able to:
- Use Companies House WebFiling for accounts
- Submit paper accounts
- File abridged accounts
Free Alternatives to HMRC's Service
You don't have to pay for CT600 filing software. TinyTax offers completely free CT600 filing for micro-entity companies, including:
- CT600 return preparation and submission
- iXBRL accounts generation
- Companies House accounts filing
- Automatic error checking
- No hidden fees or subscriptions
Frequently Asked Questions
When exactly does HMRC's free filing close?
The service closes at midnight on 31 March 2026. Any returns filed after this date must use commercial software.Can I still access my old returns after closure?
No. Once CATO closes, you will not be able to view or download previous submissions. Download your history now.Do I need to tell HMRC I'm switching to different software?
No. HMRC does not require notification when you change filing software.What if I miss the deadline?
If you attempt to file using CATO after 31 March 2026, your submission will be rejected. You'll need to use commercial software, which could delay your filing and potentially incur late filing penalties.Is there any chance HMRC will extend the deadline?
HMRC has confirmed the closure date. The Economic Crime and Corporate Transparency Act requires these changes, so an extension is unlikely.Summary
- HMRC's free CT600 filing service closes 31 March 2026
- Download your filing history now
- Choose commercial software and make the switch early
- TinyTax offers free CT600 filing as an alternative
- Companies House WebFiling closes separately on 1 April 2027
Need help switching? TinyTax makes CT600 filing simple and free. Create your account today →