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HMRC letter codes · Corporation Tax (CT)

CT603Notice to deliver a Company Tax Return

Last reviewed 14 October 2026 · How Tax Letters checks its facts

In short

HMRC's CT211 notes name the CT603 as the Notice to deliver a Company Tax Return, and say a company must file a return or returns if HMRC issues one.

“Your company must file a return or returns if HMRC issue a CT603 Notice to deliver a Company Tax Return.”

GOV.UK: Corporation Tax: penalty determinations (CT211 Notes) · checked 14 October 2026

Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CT603. Each fact has its source and the day it was checked beside it.

What it is

HMRC's Company Taxation Manual says the CT603 notice to deliver states that the directors' and auditors' reports are required for companies incorporated under the Companies Act 2006.

“the notice to deliver (form CT603) states that the reports of the directors and the auditors are required … in relation to companies incorporated under the Companies Act 2006”

HMRC Company Taxation Manual: CTM93200, CTSA: the filing obligation: Returns · checked 14 October 2026

What it asks

GOV.UK's Company Tax Returns guide says a company or association must file a Company Tax Return if it gets a notice to deliver one (the CT603) from HMRC, and must still send a return if it makes a loss or has no Corporation Tax to pay.

“Your company or association must file a Company Tax Return if you get a ‘notice to deliver a Company Tax Return’ from HM Revenue and Customs (HMRC). You must still send a return if you make a loss or have no Corporation Tax to pay.”

GOV.UK: Company Tax Returns · checked 14 October 2026

GOV.UK says that if HMRC issues you a CT603 notice to deliver a Company Tax Return, you have a legal obligation to submit a return.

“If HMRC issues you a notice to deliver a Company Tax Return then you have a legal obligation to submit a return.”

GOV.UK: Company Tax Return obligations · checked 14 October 2026

Time limits and rules

HMRC's CT211 notes say the return called for by a CT603 notice to deliver must be delivered to the officer who issued the notice by the filing date, which is the later of four dates: 12 months from the end of the period for which the return is made; 3 months from the date the notice to deliver was served; 12 months from the end of the company's relevant period of account, if it is not longer than 18 months; and 30 months from the start of the company's relevant period of account, if it is longer than 18 months.

“The return must be delivered to the officer who issued the notice to deliver by the filing date, which is the later of: … 12 months from the end of the period for which the return is made … 3 months from the date on which the notice to deliver was served … 12 months from the end of the company’s relevant period of account, if it is not longer than 18 months … 30 months from the start of the company’s relevant period of account, if its longer than 18 months”

GOV.UK: Corporation Tax: penalty determinations (CT211 Notes) · checked 14 October 2026

If HMRC has not sent a CT603, GOV.UK's Corporation Tax penalties page lists, as an example of reasonable care, telling HMRC promptly (within 12 months of the end of the Corporation Tax accounting period) if the company has profits chargeable to Corporation Tax but HMRC has not sent a notice to deliver.

“telling HMRC promptly (within 12 months of the end of your Corporation Tax accounting period) if your company or organisation has profits chargeable to Corporation Tax but HMRC hasn’t sent you a ‘Notice to deliver a Company Tax Return’”

GOV.UK: Corporation Tax: penalties · checked 14 October 2026

Free help and HMRC contacts

For questions about the CT603, HMRC's Corporation Tax enquiries line (GOV.UK) is 0300 200 3410, open Monday to Friday, 8am to 6pm and closed on bank holidays. GOV.UK has a “Find out about call charges” link.

“Call HMRC for help with general Corporation Tax enquiries. … Telephone: 0300 200 3410 … Opening times: Monday to Friday: 8am to 6pm. Closed bank holidays … Find out about call charges”

GOV.UK: Corporation Tax: general enquiries · checked 14 October 2026

Free help first

These routes are described by GOV.UK, TaxAid and Citizens Advice themselves.

  • HMRC's extra supportHMRC offers extra support if your health condition or personal circumstances make it difficult to contact HMRC, for example a mental health condition, financial hardship or being treated in hospital.
  • Someone to deal with HMRC for youYou can authorise a friend, relative or voluntary organisation to talk to HMRC for you and help you fill in forms.
  • TaxAidTaxAid helps people with tax problems who cannot pay for advice. Tax Help for Older People merged with TaxAid in July 2025.
  • Citizens AdviceCitizens Advice gives confidential advice online, over the phone and in person, for free.