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.

Most dormant companies must still file a CT600 with HMRC, at least initially. HMRC's definition of dormant is narrower than Companies House's — if HMRC has issued a 'notice to deliver a company tax return', you must file one even with no activity. Once HMRC formally treats the company as dormant for corporation tax, the obligation pauses until you trade again.

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

TinyTax files dormant CT600 returns from £20 a year:

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

HMRC's Online Service Has Closed

HMRC's free CT600 filing service closed on 31 March 2026. A nil return now has to be filed through commercial software, or by an accountant.

Option 2: Accountant

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

Is There a Separate Dormant Form?

No. A dormant company that receives a notice to deliver a return files the standard CT600, with nil figures. There is no separate dormant version of the form.

CT600A is sometimes mistaken for one. It is the supplementary page for loans to participators (for example, a director's loan account), and a genuinely dormant company does not need it.

If your company has not received a notice to deliver a return (CT603) and is dormant for Corporation Tax, you may not need to file at all — see below.

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

Frequently Asked Questions

Do dormant companies need to file a CT600?

Usually yes, at least initially. If HMRC has sent a 'notice to deliver a company tax return', you must file a CT600 even if the company didn't trade. You can then ask HMRC to treat the company as dormant for corporation tax, which suspends future return requests until it becomes active again.

Is HMRC dormancy the same as Companies House dormancy?

No. They use different definitions and are separate filings. A company can be dormant for Companies House accounts purposes while HMRC still expects a corporation tax return — and vice versa. You may need to notify each body separately about your company's dormant status.

How do I tell HMRC my company is dormant?

You can inform HMRC online or by phone that your company is dormant for corporation tax. Once HMRC accepts this, it stops issuing notices to file a CT600. If the company later starts trading, you must tell HMRC within three months and resume filing.

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 from £20 a year
Do not assume dormancy means no filing. Check your obligations and file on time.