Registering a company for corporation tax

The legal requirement

Section 55 of the Finance Act 2004 requires a company to give HMRC notice of the beginning of its first accounting period, and of any later accounting period that does not follow straight on from the end of the previous one. The notice must say when the period began and must be given no later than 3 months after that date.

HMRC's guidance on trading and non-trading puts it as telling HMRC within 3 months of starting the tax accounting period if the company is within the charge to corporation tax and is now active.

When a company is active

• Carrying on a business activity such as a trade or professional activity (GOV.UK: trading and non-trading).
• Buying and selling goods with a view to making a profit or surplus (GOV.UK).
• Providing services (GOV.UK).
• Earning interest or managing investments (GOV.UK).
• Receiving any other income (GOV.UK).

What HMRC needs

• The company's name and registered number (SI 2004/2502 reg 2).
• The registered office address and the principal place of business (SI 2004/2502).
• The nature of the business and the date to which the company intends to prepare accounts (SI 2004/2502).
• The full name and home address of each director (SI 2004/2502).
• The date the accounting period began (SI 2004/2502).
• Details of any business taken over, the parent company if there is one, and the date the company first had to operate PAYE, where these apply (SI 2004/2502).

Registering a new client company

1. Get the UTR

   A company's Unique Taxpayer Reference (UTR) is a 10-digit number. If the client cannot find it, request it online and HMRC sends it to the registered office address held by Companies House (GOV.UK: find a UTR).

2. Confirm the start date

   Agree with the client the date the company became active, using the activities HMRC lists (GOV.UK: trading and non-trading).

3. Register in the business tax account

   HMRC's preferred route is its online service, signed in with the company's Government Gateway details. Writing to Corporation Tax Services is also accepted (GOV.UK).

4. Check the accounting period HMRC sets

   HMRC confirms the accounting period dates by letter. Contact HMRC if they are wrong (GOV.UK: accounting periods).

5. Set up agent access

   Ask the client to authorise the practice for corporation tax. See agent authorisation.

Worked example

For example, a company is incorporated on 10 May 2026 and starts trading on 1 August 2026. Its first accounting period for corporation tax begins on 1 August 2026, so HMRC must be told within 3 months of that date (FA 2004 s55).

The company can be dormant for corporation tax from 10 May to 31 July 2026 (GOV.UK: first accounts and return). Its first accounts at Companies House still run from incorporation. Depending on when corporation tax services were added, it may need one or two returns for the first accounts (GOV.UK). See first accounts deadlines.

Dormant companies

A company is dormant for corporation tax when it has stopped trading and has no other income, or is a new company that has not started trading. Tell HMRC that it is dormant (GOV.UK: dormant for Corporation Tax).

If the company has already filed a return or has received a notice to deliver one, it still files a Company Tax Return online, which shows HMRC it is dormant (GOV.UK). It also keeps filing accounts and a confirmation statement at Companies House. See dormant company accounts.

When a dormant company becomes active again, a new accounting period begins that does not follow on from a previous one, so the 3-month notice under section 55 applies again.

Questions