Registering a New Company for Corporation Tax

A new limited company must be registered for Corporation Tax with HMRC within 3 months of starting to do business. Forming the company at Companies House is a separate step, and although the two are often linked when you incorporate online, it is the directors who are responsible for making sure HMRC has the right start date. This guide explains what counts as starting, what you need to hand, and which dates follow once you are registered.

Key takeaways

• Register within 3 months of starting to do business.
• Doing business includes buying, selling, advertising, renting a property and employing someone.
• HMRC posts a 10-digit Unique Taxpayer Reference (UTR) to the registered office.
• Corporation Tax is normally due 9 months and 1 day after the accounting period ends. The return is due after 12 months.
• A long first period often means two Company Tax Returns.

What is Corporation Tax registration?

Corporation Tax registration is the process of telling HMRC that your company has started doing business, so that HMRC can open a Corporation Tax record, set the company's first accounting period and tell you when to pay. HMRC does not send a bill for Corporation Tax. The company has to work out its own profit, report it and pay on time, and none of that can happen until the registration is in place.

Companies House and HMRC: two separate registrations

GOV.UK explains that when you register a company online with Companies House you will usually be set up for Corporation Tax at the same time. If you registered by post, through an agent or with third-party software, or did not activate a business tax account, you need to add Corporation Tax services to your business tax account yourself.

What counts as "starting to do business"?

The trigger is wider than making a sale. HMRC treats a company as doing business when it starts buying, selling, advertising, renting a property or employing someone. A company that signs a lease on a unit, or pays for a website and adverts ahead of launch, has started, even if no customer has paid anything yet.

Keep a note of the date and what happened on it. That date becomes the start of the company's first accounting period, so it affects every deadline that follows.

What you will need

• The company registration number from the certificate of incorporation.
• The date the company started to do business.
• The date the first accounts are made up to.
• The company's 10-digit UTR, which is on letters from HMRC. If it has not arrived 15 working days after registering the company, you can request it online.
• A Government Gateway user ID and password for the company. This is separate from any personal Government Gateway ID you hold.

Check the registered office address at Companies House is right before you start. HMRC sends the UTR and activation code there, and a letter that goes to an old formation agent's address is a common cause of delay.

Step by step: registering

1. Confirm whether Corporation Tax was set up at incorporation. Look for HMRC letters at the registered office.
2. Find the UTR, or request it online if it has not arrived.
3. Sign in to the business tax account with the company's Government Gateway user ID. You can create one at sign-in if needed.
4. Add the Corporation Tax service from the list of services you can add, and enrol.
5. Enter the details: registration number, date business started and the date accounts are made up to.
6. Wait for the activation code. GOV.UK says HMRC sends it within 10 days, by post to the registered office.
7. Activate the service and check the accounting period dates HMRC has given you. Tell HMRC if they look wrong.
8. Put the payment and filing deadlines in your calendar, and register for PAYE and VAT separately if they apply.

Key dates after you register

Corporation Tax is normally payable 9 months and 1 day after the end of the accounting period. The Company Tax Return is due 12 months after the end of the period, so the tax falls due before the return does. See our guides to the Corporation Tax payment deadline and the Company Tax Return (CT600).

An accounting period for Corporation Tax cannot be longer than 12 months. A company's first accounts usually run from incorporation to the end of the same month a year later, which is slightly more than 12 months. If the company traded from day one, that means two returns and two payment dates. GOV.UK covers this under your limited company's first accounts and Company Tax Return.

If the company is not trading

A new company that has not started trading is usually dormant for Corporation Tax. If a company that was active stops trading and has no other income, you can tell HMRC it is dormant. Dormant does not mean forgotten: Companies House still expects accounts and a confirmation statement. Our guide to dormant company accounts explains what to file.

Worked example (illustrative)

"Tideway Couriers Ltd", an illustrative example, is incorporated on 14 July 2026. Companies House sets its first year end as 31 July 2027. The director does nothing with the company until 1 September 2026, when it leases a van and starts advertising. That is the day it starts doing business, so it must be registered for Corporation Tax by the end of November 2026.

Its first Corporation Tax accounting period starts on 1 September 2026. If it runs to the year end of 31 July 2027, it covers 11 months, so usually one Company Tax Return is needed, for the trading period. Corporation Tax for that period would be payable by 1 May 2028 and the return would be due by 31 July 2028. The director should still check the notice HMRC sends, in case it also asks for a return covering the weeks the company was dormant.

Had the company started doing business on the day it was formed, the first accounts would cover 14 July 2026 to 31 July 2027, which is more than 12 months. It would then need two returns: one for 14 July 2026 to 13 July 2027, with tax payable by 14 April 2028, and one for 14 to 31 July 2027, with tax payable by 1 May 2028.

The company and dates are invented for illustration and are not a real client.

Common mistakes

• Assuming Companies House has done it all. Check that HMRC has the company set up and holds the correct start date.
• Waiting for the first sale. Advertising, renting or hiring can start the 3 month clock earlier.
• Ignoring letters at the registered office. The UTR and activation code arrive by post.
• Using a personal Government Gateway ID for the company.
• Registering late. You may get a penalty. Check the current rules on GOV.UK.
• Expecting a bill. HMRC does not send one. You calculate and pay.
• Missing the second return when the first accounts cover more than 12 months.

How we can help

We register new companies for Corporation Tax, confirm the accounting periods with HMRC, and prepare the tax computations and Company Tax Returns that follow. Corporation Tax services start from £250 per year on a fixed fee. If you have only just incorporated, our guide to the first year of a limited company sets out everything else to do. See our Corporation Tax service, view our pricing, or contact us as soon as the company starts doing business.