How to register your company for Corporation Tax

When do you have to register for Corporation Tax?

You must tell HMRC within 3 months of the start of your company's first Corporation Tax accounting period. For a new company, that period starts on the day it begins to do business, not necessarily the day it was incorporated. A company that has not yet done any business is usually dormant for Corporation Tax.

HMRC's guidance puts it this way: you must tell HMRC within 3 months of starting your tax accounting period if your limited company is within the charge of Corporation Tax and is now active. The same rule applies when a dormant company becomes active again.

Source: Corporation Tax: trading and non-trading

What counts as starting to do business?

GOV.UK says a company starts to do business when it buys, sells, advertises, rents a property or employs someone. HMRC's detailed guidance adds providing services, earning interest, managing investments and receiving any other income. Once any of these happens, the company is usually active for Corporation Tax and its first accounting period starts.

Some early steps do not count. HMRC treats preliminary work, such as writing a business plan or negotiating contracts, and costs spent deciding whether to start a business, as pre-trading activity. A new company that has only done these things has not yet started trading.

HMRC says its meaning of active or dormant is not necessarily the same as Companies House's, so check the company's position with each separately.

• Carrying on a trade or professional activity
• Buying and selling goods with a view to making a profit
• Providing services
• Earning interest or managing investments
• Receiving any other income

Source: Corporation Tax: trading and non-trading

Was my company set up for Corporation Tax when I formed it?

Possibly. GOV.UK says that when you register a company online with Companies House, you will usually be set up for Corporation Tax at the same time, unless the company is dormant. If you formed it by post, through an agent or with third-party software, or online without activating a business tax account, you add Corporation Tax yourself.

If you are not sure, sign in to the company's business tax account and look for the Corporation Tax service. If it is not there, add it when the company starts to do business.

Source: Set up a private limited company: Register your company

What you need before you register

GOV.UK lists four things you need to add Corporation Tax services to the company's business tax account. You also need the company's own Government Gateway user ID and password. If the company does not have one, you can create one when you sign in.

• The company registration number from Companies House.
• The date the company started to do business. Its first Corporation Tax accounting period starts from this date.
• The date the company's first accounts are made up to, which is usually its accounting reference date.
• The company's 10-digit Unique Taxpayer Reference (UTR). It is on letters from HMRC. If it has not arrived 15 working days after the company was registered, you can ask HMRC for a copy of the UTR.

Source: Add Corporation Tax services to your business tax account

How to register for Corporation Tax step by step

These steps follow GOV.UK's guide to adding Corporation Tax services to a business tax account.

1. Check the date the company started to do business, using the activities listed above.
2. Check the registered office address on the Companies House register is correct. HMRC sends its letters there, and you change the address through Companies House.
3. Gather the company number, UTR, start date and the date the first accounts are made up to.
4. Sign in to the company's business tax account with its Government Gateway user ID and password.
5. Select 'Services you can add' in the left-hand menu, find Corporation Tax and select 'Enrol for service'.
6. Wait for HMRC's letter. HMRC posts an activation code within 10 days (21 days if you live abroad), instructions for activating the service and your Corporation Tax payment deadline.
7. Activate the service with the code, then check the accounting period dates HMRC gives you and tell HMRC if they are wrong.

Source: Add Corporation Tax services to your business tax account

Registering by letter instead

HMRC says the best way to register is online, but you can also write to Corporation Tax Services, HM Revenue and Customs, BX9 1AX. The letter must give the company's name and registration number, the date its accounting period started, the date it will prepare accounts to, its principal place of business, what the business does and the name and home address of each director.

Where they apply, the letter also needs details of any business the company took over, its parent company and the date it first had to operate PAYE. A director or company secretary must sign it and declare that the information is correct and complete to the best of their knowledge.

Source: Corporation Tax: trading and non-trading

How your first accounting period is set

The date you give HMRC as the day the company started to do business is the start of its first Corporation Tax accounting period. After you add Corporation Tax services, HMRC writes to you with the dates of that period. Check them, and tell HMRC if you think they are wrong. An accounting period can never be longer than 12 months.

GOV.UK gives an example of a company set up on 11 May 2024 that started trading on 22 July 2024 and added Corporation Tax services on 26 August 2024. With an accounting reference date of 31 May 2025, it prepared accounts from 11 May 2024 to 31 May 2025 and filed one tax return for its trading period, 22 July 2024 to 31 May 2025.

Getting the start date right matters, because it fixes your filing and payment deadlines. If the company was dormant before it traded, or its first accounts run for more than 12 months, it may need 2 returns. Our guide to Corporation Tax accounting periods explains when that happens.

Source: First accounts: if you started trading after you set up

What if the company is dormant from incorporation?

A new limited company that has not started trading is usually dormant for Corporation Tax, so it does not need to register yet. HMRC may write to say it is treating the company as dormant. If it has not, you can tell HMRC the company is dormant online, using its name and 10-digit UTR.

After you tell HMRC, the company does not have to file another Company Tax Return unless HMRC asks for one or it begins trading. A notice to deliver a return that has already been sent must still be answered: see what to do with an HMRC notice to file. We can also tell HMRC your company is dormant for you.

Being dormant for Corporation Tax does not stop Companies House filings. The company still files annual accounts and a confirmation statement, starting with its first accounts, due 21 months after incorporation.

Source: Dormant companies: dormant for Corporation Tax

Restarting Corporation Tax after a dormant period

If a dormant company starts trading again, tell HMRC by registering for Corporation Tax again in the company's business tax account. HMRC's guidance on telling them a company is active applies here too, so do it within 3 months of the restart.

The new Corporation Tax accounting period begins on the day business restarts, but the company's Companies House dates stay the same. GOV.UK's example: with an accounting reference date of 30 September and a restart on 1 May, you prepare accounts for 1 October to 30 September as usual, and file a Company Tax Return for 1 May to 30 September.

Source: Restarting a non-trading or dormant company

What happens if you register late?

HMRC's failure-to-notify rules apply if a company that is chargeable to Corporation Tax for an accounting period has not been sent a notice to file a return and does not tell HMRC within 12 months of the end of that period. A penalty may then be charged, worked out as a percentage of the tax lost because of the failure.

The percentage depends on whether the failure was deliberate and whether you told HMRC before they found out. HMRC will not charge a penalty for a non-deliberate failure if you had a reasonable excuse and told them without unreasonable delay once it ended. The safest course is to register as soon as the company starts to do business.

Source: Compliance checks: penalties for failure to notify (CC/FS11)

Common mistakes when registering for Corporation Tax

These mistakes come up often, and most of them lead to wrong dates or missed deadlines.

• Giving the incorporation date as the start date when the company only began doing business later.
• Assuming forming the company online always set it up for Corporation Tax. Check the business tax account.
• Using the company number where HMRC asks for the 10-digit UTR. They are different references.
• Leaving an old registered office address on the register, so HMRC's activation code goes astray.
• Thinking a dormant company does not need to tell HMRC when it starts trading again.
• Not filing a Company Tax Return because the company made a loss. GOV.UK says you must still file one.

Source: Add Corporation Tax services to your business tax account

How SimpleFilings can help

If your company has started or restarted business and HMRC does not yet know, our Corporation Tax registration service prepares the notification that it is active, for a director or company secretary to approve before anything is sent. Our £4.99 SimpleFilings service fee applies to each filing. We do not prepare accounts or Company Tax Returns, or work out or pay Corporation Tax, and HMRC may still ask for a signed notification or further checks.