- You must register for Corporation Tax with HMRC within 3 months of starting to trade.
- Registration is separate from Companies House incorporation and must be done with HMRC.
- Once registered, HMRC sets your accounting period and future filing and payment deadlines.
You must register for Corporation Tax with HMRC within three months of starting to trade. This deadline catches many new limited company directors out, yet missing it can lead to penalties and unnecessary follow-up from HMRC.
Registering for Corporation Tax is separate from incorporating your company with Companies House. Once your business starts trading, for example by invoicing clients, advertising, or buying stock, you have a legal obligation to notify HMRC.
If you want this handled correctly without second-guessing deadlines or definitions, Sleek’s accounting services can manage the registration and ongoing compliance for you.
In this guide, you’ll learn exactly when you need to register for Corporation Tax, what HMRC considers “starting to trade”, how to register online step by step, and what happens after registration. This keeps your company compliant from day one and avoids problems later when filing and paying Corporation Tax.
When do you need to register for Corporation Tax?
You must register for Corporation Tax within three months of starting to trade. This deadline is strict and applies even if your company has not yet made a profit.
HMRC defines “starting to trade” broadly. It includes issuing invoices, advertising your services, buying stock, renting premises, or paying staff. Simply incorporating a company does not start the clock, but taking steps to earn income does.
If you are unsure whether your activity counts as trading, our guide on trading vs non-trading for Corporation Tax explains how HMRC draws the line.
Many directors assume the three-month registration deadline starts when the company is incorporated. In reality, HMRC starts the clock when your company begins trading, which may be weeks or months later. Keeping a clear record of when trading activity actually started helps avoid accidental late registration and penalties.
Why registering for Corporation Tax matters
Registering for Corporation Tax tells HMRC that your company is active and needs to be brought into the tax system. Without registration, HMRC cannot set your accounting period or issue deadlines for filing and payment.
Failing to register on time can trigger penalties and create problems later when you try to file your Company Tax Return. Early registration keeps your records clean and avoids unnecessary back-and-forth with HMRC.
What you need before registering for Corporation Tax
Before you start, make sure you have the correct details ready. This keeps the registration process quick and avoids rejected submissions.
You will need:
- Your company registration number from Companies House
- The date your company started trading
- Your company’s accounting period end date
- Your registered office address
- A Government Gateway user ID
Once registration is complete, HMRC will issue your company with a Unique Taxpayer Reference (UTR).
If you want to understand how this number is used later, our guide to tax reference numbers in the UK explains where it appears and why it matters.
How to register for Corporation Tax with HMRC
Most companies register for Corporation Tax online using HMRC’s digital services. The process is straightforward and usually takes only a few minutes.
You can register directly using HMRC’s official service on its Register for Corporation Tax page.
The steps are:
- Sign in or create a Government Gateway account
- Select Corporation Tax from your business tax options
- Enter your company details and trading start date
- Submit the registration to HMRC
HMRC uses this information to determine your Corporation Tax accounting period and future deadlines.
How long does Corporation Tax registration take?
After submitting your registration, HMRC usually issues your Corporation Tax reference within a few days. This is your company’s Unique Taxpayer Reference, often referred to as a UTR.
You will receive the UTR by post at your registered office address. Keep it safe, as you will need it whenever you file, pay, or contact HMRC about Corporation Tax.
What happens after you register for Corporation Tax?
Once registered, your company is officially on HMRC’s system. From this point, you have ongoing obligations, even if no tax is due.
After registration, you must:
- Keep accurate financial records
- Prepare annual accounts
- File a Company Tax Return (CT600)
- Pay Corporation Tax by the deadline
If you want a full breakdown of the next steps, see how to pay Corporation Tax for the complete timeline from registration to payment.
Do dormant companies need to register for Corporation Tax?
Dormant companies do not usually need to register for Corporation Tax, but only if they remain dormant for Corporation Tax purposes. HMRC’s definition of dormancy is different from Companies House.
A company may lose dormant status if it starts trading, earns interest, rents property, or sells assets. Once that happens, you must register and file a Company Tax Return again.
Our guide on trading vs non-trading for Corporation Tax explains how this works.
What if you miss the registration deadline?
If you fail to register within three months of starting to trade, HMRC can issue penalties. These often start at £100 and increase if the delay continues or leads to late filing.
Registering late can also complicate your first Corporation Tax return, as HMRC may estimate liabilities or issue reminders before your records are in order.
How Sleek helps you register for Corporation Tax correctly
Registering for Corporation Tax is simple, but getting the timing wrong can cause long-term issues. Sleek ensures your registration is completed accurately, on time, and aligned with your wider accounting setup.
Our accountants handle registration, track deadlines, and manage your ongoing compliance so nothing slips through the cracks. That way, you stay focused on running your business while we keep HMRC satisfied.
Disclaimer: The preceding information is not legal advice. This content is aimed to provide general guidance. For more formal or legal advice, contact Sleek directly.
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FAQs on registering for Corporation Tax
When do I need to register for Corporation Tax?
You must register for Corporation Tax within three months of starting to trade. Trading includes activities such as invoicing clients, advertising, buying stock, renting premises, or paying staff. The deadline is based on business activity, not the company’s incorporation date.
How do I register for Corporation Tax with HMRC?
You register for Corporation Tax online through HMRC using your Government Gateway account. During registration, you provide your company details, trading start date, and accounting period end. HMRC then sets your Corporation Tax record and issues your company’s tax reference.
What information do I need to register for Corporation Tax?
To register, you’ll need your company registration number, the date you started trading, your accounting period end date, and access to a Government Gateway account. HMRC uses this information to determine your filing and payment deadlines.
Do I need to register for Corporation Tax if my company hasn’t made any money?
Yes. You must still register for Corporation Tax even if your company has not made a profit. Registration is required once trading begins, and you’ll still need to file a Company Tax Return to confirm your position.
Is registering for Corporation Tax the same as filing a Company Tax Return?
No. The rate depends on profit level and company type. Close Investment Holding Companies always pay the main rate of 25%. Companies with associated companies may reach higher rates sooner because profit thresholds are shared.
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Do dormant companies need to register for Corporation Tax?
Dormant companies do not need to register for Corporation Tax if they remain dormant for Corporation Tax purposes. However, if the company starts trading or receives income, you must register within three months of that activity.
What happens if I don’t register for Corporation Tax on time?
If you miss the three-month registration deadline, HMRC can issue penalties and may estimate your tax position. Late registration can also create issues when filing your first Company Tax Return, increasing the risk of fines and compliance problems.
