Does a dormant company need to file a Company Tax Return (CT600)?

Does a dormant company need to file a CT600?

A dormant company needs to file a Company Tax Return (CT600) when HMRC has sent a notice to deliver one, or when it has already filed returns and has not told HMRC it is dormant. Once HMRC has been told, no further return is needed unless HMRC sends a new notice or trading restarts.

GOV.UK's dormancy guidance covers the case where you have filed a Company Tax Return or had a 'notice to deliver a Company Tax Return'. It says: "You'll still need to file a Company Tax Return online - this will show HMRC that your company is dormant for this period."

HMRC's guidance on trading and non-trading adds: "If you have not informed HMRC you are dormant you will still be required to submit a Corporation Tax tax return. Failure to do so may result in penalties being raised against the company." For what the letter itself means and how its deadline is set, see our guide to the HMRC notice to file a Company Tax Return.

Source: Dormant for Corporation Tax

What dormant for Corporation Tax means

HMRC's test is about trading and income. GOV.UK says a company is usually dormant for Corporation Tax if it has stopped trading and has no other income, or is a new limited company that has not started trading. Trading includes buying, selling, renting property, advertising, employing someone or getting interest.

That last point catches many owners out: a company whose only activity is bank interest is not dormant for Corporation Tax. HMRC's test is also separate from the Companies House test used for dormant accounts. Our guide on what a dormant company is compares the two.

Source: Dormant for Corporation Tax

How to tell HMRC your company is dormant

HMRC has an online service to tell it the company is not trading and is dormant for Corporation Tax. You need the company name, its 10-digit Unique Taxpayer Reference (UTR) and, if it ever traded, the date it stopped trading. If you cannot use the online service, you can tell HMRC by phone or by post. A tax agent with an agent code can do it for you.

After you tell HMRC, GOV.UK says the company will not have to file another Company Tax Return unless HMRC asks it to or it begins trading again. Telling HMRC does not tell Companies House, and you still have to send information about a dormant company to Companies House. HMRC may also write first, saying it has decided to treat the company as dormant and that it does not have to file Company Tax Returns.

Source: Tell HMRC your company is dormant for Corporation Tax

Companies House and HMRC duties for a dormant company

A dormant company has duties to both bodies, and they do not overlap. Dormant accounts go to Companies House. A Company Tax Return goes to HMRC, and only when HMRC requires one.

Source: Dormant for Companies House

Filing a dormant company tax return now that HMRC's free service has closed

HMRC's free 'File your accounts and Company Tax Return' service closed on 31 March 2026. From 1 April 2026, HMRC says to use commercial software that can file a CT600, a Corporation Tax computation and the company accounts. You can only file a paper return if you have a reasonable excuse or are filing in Welsh. Our guide on how to file a Company Tax Return after HMRC's service closed covers the options, including using an agent.

Source: Filing company accounts and tax returns if you previously used the HMRC online service

Restarting: when Company Tax Returns start again

When a dormant company starts doing business again, register it for Corporation Tax again. HMRC's guidance says to tell it within 3 months of the start of the company's tax accounting period. That period begins when business restarts, not at the usual year end.

GOV.UK gives an example. A dormant company's accounting reference date is 30 September and it restarts business on 1 May. It prepares statutory accounts for 1 October to 30 September as usual, sends them to Companies House, and sends HMRC a Company Tax Return for 1 May to 30 September. After that, accounts and a return cover 1 October to 30 September each year.

Source: Restarting a non-trading or dormant company

Common dormant company tax return mistakes

Most problems come from treating Companies House and HMRC as one body, or from treating a dormancy notification as if it cancels a return already requested.

Late returns are penalised even when no tax is due. GOV.UK's penalty table starts at £200 for a return 1 day late. That £200 amount applies to returns whose filing deadline is on or after 1 April 2026, when the fixed Corporation Tax late filing penalties doubled from £100. GOV.UK also says you must still send a return if the company makes a loss or has no Corporation Tax to pay.

• Assuming dormant accounts tell HMRC. Filing dormant accounts with Companies House does not notify HMRC or deal with a notice to deliver a return.
• Ignoring a notice because the company is dormant. A return HMRC has already asked for must still be filed online. It is how HMRC sees that the company was dormant for that period.
• Never telling HMRC at all. HMRC says a company that has not told it about dormancy will still be required to submit a return.
• Forgetting about interest. GOV.UK counts getting interest as trading, so a company earning bank interest is not dormant for Corporation Tax.
• Looking for the old HMRC filing service. It closed on 31 March 2026, so allow time to choose software or an agent.

Source: Company Tax Returns: penalties for late filing