Every UK limited company must register for corporation tax with HMRC within 3 months of starting to trade — even if you don't owe any tax yet. Fail to register on time, and you could face penalties.

This guide walks you through the entire registration process, step by step.

When Must You Register?

You must register for corporation tax within 3 months of your company:

Starting to trade (selling goods, providing services)
Earning any income (including bank interest or investment income)
Starting any business activity

Important: The clock starts from when your company begins any business activity — not from when you incorporated at Companies House. However, most companies should register shortly after incorporation since HMRC considers even buying equipment or setting up a website as "starting to trade."

What You Need to Register

Before starting the registration, have these ready:

Company Registration Number (CRN) — the 8-digit number from Companies House
Date of incorporation — when your company was formed
Date you started trading — or expect to start
Company's registered address
Principal place of business (if different from registered address)
Nature of business — what your company does (SIC code)
Accounting period end date — typically your company year-end
Directors' details — names, addresses, National Insurance numbers

Step-by-Step Registration Process

Step 1: Sign Up for a Government Gateway Account

If you don't already have one:

Go to HMRC online services
Click "Create sign in details"
You'll receive a User ID — save this carefully
Set up your password and recovery options

Step 2: Register for Corporation Tax Online

Go to Register for Corporation Tax
Sign in with your Government Gateway credentials
Fill in your company details:
- Company name and CRN
- Registered address
- Date you started trading
- Your accounting period dates
- Nature of business (SIC code)

Step 3: Wait for Your UTR

After registering, HMRC will send your company's Unique Taxpayer Reference (UTR) by post. This typically takes:

7-10 working days by post to a UK address
Up to 21 working days for overseas addresses

Your UTR is a 10-digit number (e.g., 1234567890). You'll need this for:

Filing your CT600 tax return
Paying your corporation tax
Corresponding with HMRC about your company's tax affairs

Step 4: Activate Your Online Account

Once you receive your UTR:

Log into your Government Gateway account
Add Corporation Tax to your account using your UTR
HMRC sends an activation code by post (another 7-10 days)
Enter the activation code to complete setup

Total time from registration to full online access: approximately 2-4 weeks.

What Happens After Registration?

Once registered, HMRC will:

Send you a CT600 notice — a formal notice to file your company tax return
Set your filing deadline — 12 months after your accounting period ends
Set your payment deadline — 9 months and 1 day after your accounting period ends

Your First Accounting Period

Your first accounting period starts on the date of incorporation and can be up to 18 months long. Most companies choose to align with a calendar date (e.g., 31 March, 31 December).

If your first period exceeds 12 months, you'll need to file two CT600 returns:

One for the first 12 months
One for the remaining period

Penalties for Late Registration

If you don't register within 3 months of starting to trade:

Delay	Penalty
Up to 3 months late	Normally a warning
3-12 months late	Up to £100
Over 12 months late	Up to £200

HMRC may also estimate your tax liability and send a "determination" — essentially guessing what you owe. This determination stands until you file your actual return.

Common Questions

My company is dormant — do I still need to register?

Not immediately. If your company has never traded and has no income, you can tell HMRC it's dormant. However, you should still register if:

The company has any bank interest income
You plan to start trading soon
HMRC sends you a notice to deliver a CT600

I already have a personal UTR — is that the same?

No. Your personal UTR (for Self Assessment) is different from your company's corporation tax UTR. They're separate tax registrations.

Can I register before I start trading?

Yes. You can register as soon as your company is incorporated, even if you haven't started trading yet. This is often recommended to avoid missing the 3-month deadline.

What if I missed the deadline?

Register as soon as possible. The penalties for late registration are relatively small, and HMRC is generally lenient for first-time offences. The bigger risk is missing your filing deadline because you didn't know about it.

I registered at Companies House — isn't that enough?

No. Companies House and HMRC are separate organisations. Registering at Companies House creates your company, but you must separately register with HMRC for corporation tax.

However, if you incorporated online through Companies House, you may have been given the option to register for corporation tax at the same time. Check your Companies House account to see if this was done.

Ready to File Your CT600?

Once you're registered and have your UTR, you're ready to file your corporation tax return. Taxpipe makes this simple — create your account, enter your company details, answer straightforward questions, and we handle the CT600 filing for just £59.

No accountancy jargon, no complex forms. Get started today →

Next step: Set up your HMRC online account →

How to Register for Corporation Tax: Step-by-Step Guide for New Companies