How to Register for Corporation Tax in the UK: A Step-by-Step Guide for Small Businesses
If you’ve recently started a limited company in the UK, congratulations! It’s a big milestone. But now comes the admin—and one of the most important tasks you need to handle early on is registering for Corporation Tax.
It might sound a bit intimidating at first, especially if you’re new to business or haven’t dealt with HMRC before. But the process is actually quite straightforward once you know what to expect. In this guide, we’ll walk you through everything you need to know—what Corporation Tax is, when you need to register, how to do it, and what happens next.
Let’s get into it.
What Is Corporation Tax?
Corporation Tax is a tax that limited companies pay on their profits. That includes:
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Money your business makes from trading (selling goods or services)
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Investment income
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Selling assets for more than they cost (called “chargeable gains”)
As of 2025, the Corporation Tax rate in the UK is 25% for profits over £250,000. For companies with profits of £50,000 or less, it’s 19%, and anything in between is subject to a tapered rate.
Unlike income tax, there’s no personal allowance—you pay Corporation Tax on all your company profits.
Who Needs to Register?
You must register for Corporation Tax if you:
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Start a new limited company (registered with Companies House)
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Restart a dormant company that starts trading again
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Set up a UK branch of an overseas company
If you’re operating as a sole trader or partnership, you don’t pay Corporation Tax—you’ll be dealing with Self Assessment instead.
When Should You Register?
You must register within 3 months of your company starting to do business. HMRC calls this “becoming active.”
Here’s what “doing business” might include:
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Buying or selling goods/services
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Advertising
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Renting a business property
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Employing staff
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Receiving interest or investment income
Basically, if you’re making money or planning to, you’re likely considered active.
Important: Don’t wait until your first sale. As soon as you start trading (even just preparing to), your clock starts ticking.
What Happens If You Don’t Register?
Failing to register for Corporation Tax on time can result in penalties and interest. HMRC may charge you a fine, and you could be charged late payment interest on any unpaid tax.
It’s best to get it sorted early—it’s free, and takes less than 30 minutes in most cases.
What You’ll Need Before Registering
Before you can register, you’ll need the following info:
✅ Company’s Unique Taxpayer Reference (UTR)
This 10-digit number is sent by HMRC to your company’s registered office address shortly after you register with Companies House. It usually arrives within 10 days.
If you’ve lost it, you can request it again through your HMRC business tax account.
✅ Company Registration Number (CRN)
This is the unique number Companies House gives your business. It’s on your certificate of incorporation.
✅ The date your business started trading
HMRC will use this to calculate your Corporation Tax accounting period.
✅ The nature of your business
You’ll need to describe what your business does (for example, “online retail of clothing”).
✅ Company address and director details
Basic info about your business and who’s running it.
How to Register for Corporation Tax: Step-by-Step
Here’s a simple guide to help you through the process:
Step 1: Set up a Government Gateway Account (if you haven’t already)
This is your online portal to deal with HMRC services.
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Go to the HMRC Government Gateway website
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Choose “Create sign in details”
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Follow the steps to get your user ID and password
Once you have that, you can log in and manage your company taxes online.
Step 2: Log into your Business Tax Account
After you’ve signed in, you’ll access your HMRC Business Tax Account. From here, you can:
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Register for Corporation Tax
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Add other taxes like VAT or PAYE (if needed)
Step 3: Register for Corporation Tax
Inside your account:
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Click on “Register for Corporation Tax”
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Fill in the form with the information listed above
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Submit the registration
Once submitted, you should receive confirmation that your application is being processed.
What Happens After You Register?
After registering, HMRC will:
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Confirm your accounting period (this is usually your company’s first year from the date of incorporation)
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Send you reminders about when to file your Company Tax Return (CT600)
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Provide information on how and when to pay Corporation Tax
You won’t receive a bill—you’re responsible for working out how much tax your company owes and paying it on time.
What Are Your Ongoing Responsibilities?
Once you’ve registered for Corporation Tax, your responsibilities include:
Filing a Company Tax Return (CT600)
Every year, you need to file a CT600 with HMRC. It shows:
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How much profit your company made
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Any reliefs or allowances you’re claiming
Paying Corporation Tax
You must pay any tax due 9 months and 1 day after the end of your accounting period. For example, if your year ends on 31st December, you must pay your tax by 1st October the following year.
Keeping Good Financial Records
This includes:
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Income and expenses
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Bank statements
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Sales invoices and receipts
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Payroll (if applicable)
You’ll need these records to file accurate tax returns and to back up your figures if HMRC asks.
What If Your Company Is Dormant?
If you’ve registered a company but haven’t started trading yet, you don’t need to register for Corporation Tax right away. You can notify HMRC that your company is dormant for now.
Once you do start trading, though, make sure to register within the 3-month window.
Can You Use an Accountant?
Absolutely. Many UK businesses choose to hire an accountant to:
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Register for Corporation Tax
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Handle VAT, PAYE, and bookkeeping
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Communicate with HMRC on your behalf
While it’s not legally required, having an accountant can save you time, reduce stress, and help you avoid costly mistakes—especially as your business grows.
Common Mistakes to Avoid
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❌ Waiting too long to register
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❌ Assuming HMRC will contact you when it’s time to register
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❌ Thinking Corporation Tax only applies once you’re profitable (it doesn’t—you still need to file)
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❌ Not keeping proper records from day one
Getting it right early on sets you up for smoother business operations and fewer tax surprises later.
Conclusion
Registering for Corporation Tax in the UK is one of the first official steps to running a compliant limited company. While it may seem like just another bit of red tape, it’s a crucial part of staying on the right side of HMRC.
The good news? It’s easier than most people expect—and once it’s done, you won’t need to do it again unless your company becomes inactive and restarts later.
Just remember: do it within 3 months of starting to trade, keep your records clean, and file your returns on time. If you’re unsure, don’t be afraid to speak to an accountant—they’ll help make sure everything’s set up correctly from the start.
