HMRC CT600 Online Service: Pros, Cons, and Why It Is Closing

HMRC has provided a free online CT600 filing service for years. However, this service is closing in March 2026, and businesses need to plan their transition to commercial software.

Here is what you need to know.

What Is the HMRC CT600 Online Service?

The HMRC CT600 online service allows companies to file corporation tax returns directly through the Government Gateway. It is:

  • Free to use
  • Basic functionality only
  • Used by small companies and sole directors
  • Accessed via HMRC website

Why Is It Closing?

HMRC announced the closure as part of modernising tax administration. The service is being retired because:

  1. Limited functionality - Cannot handle complex returns
  2. Separate from accounts filing - Companies House filing requires different tools
  3. No iXBRL generation - Modern filings require tagged formats
  4. Maintenance costs - Maintaining legacy systems is expensive
  5. MTD alignment - HMRC is moving toward Making Tax Digital
The closure date is 31 March 2026.

Pros of the HMRC Service

Free

The main advantage is zero cost. For small companies with simple affairs, this was attractive.

Official

Some users prefer filing directly with HMRC rather than through third parties.

Basic Returns

For straightforward nil returns or simple trading companies, it worked adequately.

Cons of the HMRC Service

No Companies House Filing

You still need separate software or service to file accounts with Companies House. This means two processes instead of one.

No iXBRL Generation

The service does not generate iXBRL accounts or computations. These must be created separately.

Limited Features

  • No automatic tax calculations
  • No prior year comparison
  • No draft saving
  • No deadline reminders
  • No integrated accounts

Complex Interface

The Government Gateway and CT600 forms are not user-friendly for non-accountants.

No Support for Complex Returns

  • Cannot handle extended periods properly
  • Limited loss relief options
  • No marginal relief calculator
  • Complex scenarios not supported

Alternatives to HMRC Service

TinyTax

Best for: Directors, small businesses, accountants

  • Free for dormant companies
  • From £5/year for trading companies
  • CT600 and Companies House filing combined
  • iXBRL generation included
  • Automatic tax calculations
  • No contracts

TaxFiler (IRIS)

Best for: Accountants with mixed client portfolios

  • From £10/month
  • Full practice suite (SA100, CT600, partnerships)
  • Annual contract required

TaxCalc

Best for: Accountants with volume filing

  • Practice-focused pricing
  • Comprehensive features
  • Training required

BTCSoftware

Best for: Larger practices

  • Enterprise features
  • Integration with other systems
  • Higher price point

Why Switch Now?

Even though the service closes in 2026, there are reasons to switch sooner:

1. Combined Filing

With TinyTax, file CT600 and Companies House accounts together. No more switching between systems.

2. Better User Experience

Modern software guides you through the process with helpful explanations and automatic calculations.

3. Time Savings

Automated features like prior year data import and tax calculations save hours.

4. No Last-Minute Rush

Millions of businesses will need to switch before March 2026. Avoid the rush by switching now.

5. Free Options Available

TinyTax is free for dormant companies, so there is no cost barrier to switching.

How to Transition

Step 1: Choose Your Software

Select software that matches your needs. For most small companies, TinyTax offers the best value.

Step 2: Gather Information

You will need:

  • Company number
  • UTR (Unique Taxpayer Reference)
  • Previous years figures (for comparison)
  • Government Gateway login (for HMRC submission)

Step 3: Set Up Your Account

Register with your chosen software and add your company details.

Step 4: File Your Next Return

When your next filing is due, use the new software instead of the HMRC service.

Step 5: Complete the Transition

After filing once with new software, you are transitioned. Future returns follow the same process.

Frequently Asked Questions

Can I keep using HMRC service until 2026?

Yes, but functionality may degrade and you will still need separate accounts filing.

Is there really no free option after 2026?

TinyTax offers free filing for dormant companies. Trading companies pay from £5/year.

Do I need to tell HMRC I am switching?

No. You just file through different software. The return reaches HMRC the same way.

What happens if I do not switch?

After March 2026, you will be unable to file through the HMRC service. You will need commercial software.

Summary

The HMRC CT600 online service is closing in March 2026. While it was free, it had significant limitations:

  • No Companies House filing
  • No iXBRL generation
  • Basic functionality only
Switch to software like TinyTax to get:

  • Combined CT600 and accounts filing
  • Automatic tax calculations
  • iXBRL generation included
  • Free for dormant companies
The transition is straightforward, and there is no reason to wait until the deadline.