CT600 for Dormant Companies: Do You Need to File?

Many directors assume dormant companies do not need to file corporation tax returns. This is often incorrect. Most dormant companies still need to file a CT600 with HMRC.

Here is how to determine your obligations and file correctly.

HMRC vs Companies House Dormancy

Important: HMRC and Companies House define dormancy differently.

Companies House Definition

A company is dormant if it has no significant accounting transactions (no trading, no bank interest, no expenses).

HMRC Definition

HMRC considers a company dormant only if it:

  • Is not carrying on business
  • Has no income
  • Has no chargeable gains
  • Does not claim any reliefs or allowances
A company can be dormant for Companies House but still need to file CT600 with HMRC.

When You MUST File CT600

You must file a CT600 if your dormant company:

  • Is registered for Corporation Tax with HMRC
  • Receives a notice to deliver a return (CT603)
  • Has any income (including bank interest)
  • Has assets that could generate chargeable gains
  • Is claiming any tax reliefs

When You May Not Need CT600

You might avoid CT600 filing if:

  1. Never registered for Corporation Tax - Brand new companies that have never traded may not be registered
  2. Told HMRC you are dormant - HMRC may agree not to issue returns
  3. Company is being struck off - Final returns may not be required
However, if HMRC sends you a CT603 notice to file, you must file regardless.

Filing a Nil CT600 Return

A dormant company CT600 is straightforward:

Key Box Entries

BoxDescriptionValue
145Turnover£0
155Gross profit£0
235Total profits£0
430Corporation tax£0
No tax is due because there is no profit.

How to File

Option 1: TinyTax (Free for Dormant)

TinyTax allows dormant companies to file CT600 for free:

  1. Add your dormant company
  2. Select the dormant/nil return option
  3. Confirm the accounting period
  4. Submit directly to HMRC

Option 2: HMRC Online Service

HMRC provides free CT600 filing (until March 2026):

  1. Log in to Government Gateway
  2. Access Corporation Tax service
  3. Complete the nil return
  4. Submit
Note: HMRC service is closing in 2026.

Option 3: Accountant

Using an accountant for a nil return is usually unnecessary expense, but some directors prefer professional assistance.

CT600 vs CT600A

There are two relevant forms:

CT600 (Standard Return)

The full corporation tax return. Even with nil values, this is what most dormant companies file.

CT600A (Dormant Company Exemption)

A simplified form for companies claiming exemption from filing. Only available if:

  • Company was dormant for the entire period
  • No notice to deliver a return was issued
  • Company has no tax liability
Most companies that receive a CT603 notice must file CT600, not CT600A.

Telling HMRC You Are Dormant

If your company becomes dormant, you can notify HMRC:

  1. Write to your Corporation Tax office
  2. Explain the company is dormant
  3. Request they stop issuing notices to file
HMRC may then stop sending CT603 notices. However, if you receive one, you must still file.

Filing Deadline

Dormant companies have the same CT600 deadline:

  • 12 months after the end of the accounting period
Late filing penalties apply:
  • 1 day late: £100
  • 3 months late: additional £100
  • Repeat offenders face higher penalties

Common Mistakes

1. Assuming No Filing Needed

The most common mistake is not filing at all. If HMRC expects a return, penalties will follow.

2. Filing Late

Because there is no tax to pay, directors sometimes deprioritise filing. Penalties still apply.

3. Not Notifying HMRC

If you do not tell HMRC your company is dormant, they will keep sending notices and expecting returns.

4. Missing Companies House Filing

Remember: CT600 (HMRC) and annual accounts (Companies House) are separate. You likely need to file both.

What About Previous Years?

If you have unfiled returns from previous years, file them as soon as possible:

  • Penalties increase over time
  • Interest compounds
  • HMRC can estimate your tax liability
Even late nil returns should be filed to clear your record.

When Dormancy Ends

If your company starts trading:

  1. You must file CT600 for any period with activity
  2. Register for Corporation Tax if not already registered
  3. Normal filing requirements apply going forward

Summary

Most dormant companies need to file CT600 returns with HMRC, even with nil values. Key points:

  • HMRC dormancy differs from Companies House dormancy
  • If you receive a CT603 notice, you must file
  • Nil returns still have deadlines and penalties
  • Use TinyTax to file dormant CT600 returns for free
Do not assume dormancy means no filing. Check your obligations and file on time.