How to register for Corporation Tax in the UK: the complete guide for limited companies

Every year, HMRC issues late-filing penalties to thousands of UK limited companies that either registered for Corporation Tax too late or never registered at all. The amounts are not trivial — and the interest compounds quietly in the background while the founder assumes everything is fine because Companies House has not complained. The two regulators operate on completely separate clocks, and the Corporation Tax clock is the one that catches people out.

Here is the part that trips up most first-time founders: you do not need to register for Corporation Tax when you incorporate your company. The obligation is triggered by business activity, not by the act of incorporation itself. That distinction matters because it determines when your three-month registration window opens — and getting it wrong in either direction creates problems. Register too early and HMRC expects a CT600 return for a period in which you had no activity. Register too late and you are already in breach before you file your first invoice.

This guide explains exactly when, how, and why to register your UK limited company for Corporation Tax with HMRC — and what happens at every stage after that. If you have just incorporated and are wondering which tax registrations you actually need right now, start here.

What is Corporation Tax and who pays it?

Corporation Tax is the tax on the taxable profits of a UK limited company. It covers trading profits, investment income, and chargeable gains. Unlike income tax, which applies to individuals, Corporation Tax applies to the company as a separate legal entity. The current main rate is 25% for companies with profits above £250,000, with a small profits rate of 19% for companies with profits up to £50,000. Companies in between pay a marginal rate.

Every UK limited company that is trading or earning income must register for Corporation Tax and file an annual CT600 return with HMRC. There is no exemption based on size, turnover, or the number of directors. Even a single-director company earning modest consultancy fees is within scope.

The only exception is genuinely dormant companies — those with no significant accounting transactions in the period. If your company is dormant, you can notify HMRC and they will not require a CT600 until you become active again. We covered dormant-company compliance in detail in our dormant company checklist.

When you must register: the three-month rule

You must register your company for Corporation Tax within three months of starting business activity. That phrase — "business activity" — is doing the heavy lifting, and HMRC interprets it broadly. Any of the following counts:

• Invoicing a client or receiving payment for goods or services
• Signing a business contract — a lease, a supplier agreement, a client engagement letter
• Buying or selling business assets, including stock, equipment, or intellectual property
• Advertising or promoting your products or services
• Employing staff or engaging contractors through the company
• Renting property for business use
• Earning interest on a business bank account

Notice what is not on that list: incorporating the company. Incorporation alone does not trigger the Corporation Tax registration obligation. If you set up a company in January to reserve a name but do not start trading until June, your three-month window opens in June. This is the single most misunderstood deadline in UK company compliance — we see founders register on the day of incorporation (too early) and founders who assume HMRC will contact them when it is time (too late, and HMRC often does not chase until penalties have already accrued).

What happens if you incorporated but are not yet trading?

If your company exists on the Companies House register but has not started any business activity, you are not yet required to register for Corporation Tax. However, you are still a live company with Companies House obligations — your confirmation statement is still due every 12 months, and your first annual accounts are still due 21 months from the date of incorporation. Those deadlines run from incorporation, not from trading. Our post-incorporation checklist walks through everything that applies from day one.

Can you register before you start trading?

Yes — and in some cases it makes sense, particularly if you know exactly when trading will begin. But register too far in advance and HMRC will expect a CT600 return covering that period. If the return shows zero activity, that is fine administratively, but it creates an extra filing obligation and potential confusion when your accountant is reconciling periods. The cleanest approach is to register as soon as business activity begins, giving yourself the full three-month window without creating unnecessary empty return periods.

How to register for Corporation Tax: the step-by-step process

Registration is done through HMRC, not Companies House. The two bodies share certain data, but Corporation Tax registration is a separate process that you must initiate yourself. Here is how it works.

Step 1: Gather your information

Before you start the registration, have the following to hand:

• Company name and registration number — exactly as they appear on the Companies House register
• Date of incorporation
• Date business activity started (or will start) — this sets your first accounting period for Corporation Tax purposes
• Registered office address
• Business address (if different from the registered office)
• Nature of business — your SIC code description (see our SIC codes guide if you are unsure which applies)
• Accounting reference date — usually the last day of the month in which the company's anniversary falls, unless you have changed it
• Director details — names, addresses, National Insurance numbers
• Estimated annual turnover and number of employees

Step 2: Register online with HMRC

The registration is done through HMRC's online service. You will need a Government Gateway account for the company (not your personal one). If the company does not have one, you can create it during the registration process. The form used to be the paper CT41G, and some accountants still refer to the process by that name, but the online route is now standard and significantly faster.

During registration, HMRC will ask about:

• When the company started (or intends to start) doing business
• Whether the company has taken over another business
• The company's accounting period
• Whether you need to register for PAYE or VAT at the same time

Step 3: Receive your UTR

After registration, HMRC will post a Unique Taxpayer Reference (UTR) — a 10-digit number — to your company's registered office address. This typically arrives within two to three weeks, though it can occasionally take longer. The UTR is your company's tax identity. You will need it for every interaction with HMRC, for filing your CT600 return, and your accountant will ask for it early.

This is one of the practical reasons your registered office address needs to be monitored daily. If the UTR letter sits in an unopened pile — or worse, at a home you have moved away from — you will not know your reference number, and HMRC deadlines do not pause while you chase it. We covered this in detail in our guide on the risks of using your home as a registered office.

Step 4: Set up your HMRC online account

Once you have your UTR, activate the company's Corporation Tax online service through the Government Gateway. This is where you (or your accountant) will file the CT600 return, view your accounting periods, check any penalties, and make payments. An activation code is posted to the registered office — another letter to watch for.

Your Corporation Tax deadlines: the calendar every founder needs

Once registered, your company enters a rhythm of annual deadlines. These run from the end of each accounting period, not from the calendar year. Getting them confused is the single most expensive compliance mistake a small company can make.

The CT600 return

Your Company Tax Return (CT600) must be filed with HMRC within 12 months of the end of the accounting period it covers. The CT600 includes the company's full computation of taxable profits, capital allowances, and the tax due. Most companies file through their accountant using commercial software, but the legal responsibility sits with the directors.

Corporation Tax payment

The tax itself must be paid within 9 months and 1 day of the end of the accounting period. Note that the payment deadline is earlier than the filing deadline — you must pay the tax three months before the return is due. This catches founders out regularly: the accountant has until month 12 to finalise the return, but the money needs to be with HMRC by month 9. If you are unsure of the exact amount, you can make a payment on account and adjust later.

First-year accounts: the extended deadline

Your first set of annual accounts at Companies House is due 21 months from the date of incorporation. Subsequent accounts are due 9 months after the accounting reference date. These are Companies House deadlines, separate from HMRC — but the underlying financial statements overlap, which is why most accountants prepare both the statutory accounts and the CT600 together. Our annual accounts guide covers the Companies House side in detail.

Late filing penalties: what they actually cost

HMRC's penalty regime for Corporation Tax is blunt and automatic. There is no grace period and no "first offence" concession.

Late CT600 filing penalties

If your CT600 return is filed late, HMRC charges:

• 1 day late — £100 penalty
• 3 months late — another £100 penalty (£200 total)
• 6 months late — HMRC estimates the tax due and charges 10% of that amount (minimum £200)
• 12 months late — a further 10% of the estimated tax (minimum £200)

If your company files late three times in a row, the initial £100 penalties each increase to £500. That escalation is where small companies get hurt — a pattern of late filings turns minor penalties into a running bill.

Late payment interest

On top of the filing penalties, HMRC charges interest on unpaid Corporation Tax from the day after the payment deadline (9 months and 1 day after the accounting period ends). The interest rate fluctuates with the Bank of England base rate and is currently well above what a savings account would earn — it compounds daily, and it is not deductible against the company's profits.

Companies House penalties run in parallel

Do not confuse HMRC late-filing penalties with Companies House late-filing penalties — they are separate systems with separate penalties. Late annual accounts at Companies House attract their own fixed penalties starting at £150 and climbing to £1,500 for private companies. A company that files both the CT600 and the statutory accounts late is paying two sets of penalties simultaneously.

Do you need to register for VAT and PAYE as well?

Corporation Tax is the baseline registration, but it is not the only HMRC obligation your company may have. Two other registrations frequently trip up new founders.

VAT registration

VAT registration is mandatory only once your taxable turnover exceeds £90,000 in any rolling 12-month period, or you expect to exceed it in the next 30 days. Below that threshold, registration is voluntary. Many founders register voluntarily to reclaim VAT on startup costs, but it comes with the obligation to file quarterly VAT returns and charge VAT on invoices — so it is not automatically a good idea for every early-stage company.

VAT registration is not triggered by incorporation. You can incorporate a company, register for Corporation Tax, and operate for years without ever needing to register for VAT, provided you stay below the threshold.

PAYE registration

If you intend to pay salaries — to employees or to yourself as a director drawing a regular wage — you must register for PAYE before the first payday. Ideally, register at least two weeks before that first payment to allow HMRC processing time. PAYE is not triggered by incorporation, by appointing a director, or by paying dividends — only by paying salaries.

Many single-director companies pay the director entirely in dividends with a small salary below the National Insurance threshold. That salary still requires PAYE registration. If you are paying no salary at all and taking only dividends, PAYE registration is not needed.

Common mistakes that cost founders time and money

Corporation Tax registration is straightforward on paper, but the timing and sequencing is where companies go wrong. These are the patterns we see repeatedly.

1. Assuming HMRC will tell you when to register. HMRC receives notification when you incorporate, but it does not reliably chase you to register for Corporation Tax. The responsibility is entirely on the directors. By the time HMRC does write to you, the three-month window may have already closed.
2. Registering on the day of incorporation when you are not yet trading. This creates an accounting period that starts immediately, and HMRC will expect a CT600 covering that period even if the company had no activity. It is not catastrophic — you file a nil return — but it is unnecessary admin and can confuse your accounting reference date alignment.
3. Not knowing when "business activity" actually started. If you signed a client contract in March but did not invoice until May, the activity started in March. If you bought a domain and paid for hosting through the company account in January, that is arguably January. Pin down the date early with your accountant so your registration and accounting periods are clean.
4. Missing the UTR letter because the registered office is not monitored. The UTR is posted to the registered office — not emailed, not available online until you activate the account with it. If the letter is lost, you have to request a replacement, which takes another two to three weeks. In the meantime, you cannot file or pay.
5. Confusing the payment deadline with the filing deadline. Tax is due at 9 months and 1 day. The CT600 return is due at 12 months. Pay late and interest accrues from day one. We see companies that file their return on time but pay three months late because they assumed both deadlines were the same.
6. Forgetting that Companies House and HMRC are separate systems. Filing your annual accounts with Companies House does not satisfy your CT600 obligation with HMRC (and vice versa). Both need separate filings, separate payments where applicable, and both have their own penalty regimes.

Corporation Tax and your accounting reference date

Your accounting reference date (ARD) determines the end of each financial year for your company. By default, Companies House sets this as the last day of the month in which your company's anniversary of incorporation falls. For example, if you incorporated on 15 March 2026, your ARD would be 31 March. Your first accounting period runs from incorporation to the first ARD — which could be up to 18 months.

For Corporation Tax purposes, HMRC aligns your tax accounting period to your ARD, but a single CT accounting period cannot exceed 12 months. If your first Companies House accounting period is longer than 12 months, HMRC will split it into two Corporation Tax periods — one of 12 months and one covering the remainder. That means two CT600 returns and two payment deadlines for your first year. Discuss your ARD with your accountant early to avoid surprises.

What about a business bank account?

A business bank account is not legally required for a UK limited company. There is no statute that mandates it. However, from a Corporation Tax perspective, it is practically essential. Mixing personal and business transactions makes it significantly harder to compute taxable profits accurately, increases accountancy costs, and is a red flag if HMRC ever opens an enquiry. Most banks, lenders, and payment processors also require a dedicated business account before they will work with you.

If you have not opened one yet, do it before you start trading — it makes your Corporation Tax registration cleaner, your bookkeeping cheaper, and your accountant's life considerably easier.

Statutory records you should have in order

Corporation Tax is one piece of a broader compliance picture. By the time you register with HMRC, your company should also have its statutory registers in order — these are the legally authoritative records of your company's structure:

• Register of members (shareholders)
• Register of directors
• Register of directors' residential addresses (private, not public)
• PSC register (People with Significant Control)
• Register of charges
• Register of secretaries (if one is appointed — private limited companies are not required to appoint a company secretary)

Your accounting records must be retained for at least 6 years from the end of the accounting period they relate to. The public Companies House record is not the legal record — your internal statutory registers are. If an HMRC enquiry, investor due diligence, or legal dispute arises, it is your books and registers that are examined first.

Identity verification: the 2025 change that affects everything

Since 18 November 2025, every director and person with significant control (PSC) must have their identity verified with Companies House under the Economic Crime and Corporate Transparency Act (ECCTA). This is separate from HMRC registration, but it matters in context because a company that has not completed identity verification cannot file certain changes with Companies House — including appointing new directors who might be needed to manage the company's tax affairs.

Two lawful routes exist: directly via GOV.UK One Login (free) or through an Authorised Corporate Service Provider (ACSP) like Filing HQ. Verification is a one-off per person — it does not need to be repeated for each appointment or filing. Our identity verification guide covers the full process.

A timeline for new companies: what to do and when

Pulling all of this together, here is the practical timeline for a newly incorporated UK limited company from a tax and compliance perspective:

Immediately after incorporation

• Save your certificate of incorporation, company number, and authentication code
• Ensure your registered office address is being monitored for post
• Complete identity verification for all directors and PSCs
• Open a business bank account (not legally required, but practically essential)

When business activity starts

• Pin down the exact date activity began — this is your Corporation Tax trigger date
• Register for Corporation Tax with HMRC within 3 months
• Register for PAYE if you will be paying salaries (before the first payday)
• Consider voluntary VAT registration if it benefits your cash flow

Within 12 months of incorporation

• File your confirmation statement with Companies House (due every 12 months, online fee £50) — our confirmation statement guide explains the process
• Begin preparing your first set of accounts with your accountant

9 months and 1 day after accounting period ends

• Pay Corporation Tax to HMRC

12 months after accounting period ends

• File your CT600 return with HMRC

21 months after incorporation (first year only)

• File your first annual accounts with Companies House (subsequent years: 9 months after the ARD)

Frequently asked questions

Do I need to register for Corporation Tax if my company is not trading?

No. If your company has not started any business activity, you are not yet required to register for Corporation Tax. The obligation is triggered by business activity, not by incorporation. However, you should register within three months once activity begins — and remember that "business activity" is interpreted broadly by HMRC to include signing contracts, buying assets, advertising, and earning interest.

How long does it take to get a UTR after registering?

HMRC typically posts the UTR to your registered office within two to three weeks of registration. Occasionally it takes longer. The letter is posted, not emailed, so make sure someone is monitoring your registered office address.

What is the difference between the CT600 and annual accounts?

The CT600 is your Corporation Tax return filed with HMRC — it calculates your taxable profit and the tax owed. Annual accounts (also called statutory accounts) are filed with Companies House and provide a public financial snapshot of your company. They are prepared from the same underlying bookkeeping, but they go to different regulators, have different deadlines, and attract separate penalties if filed late.

Can I register for Corporation Tax, VAT, and PAYE at the same time?

Yes. During the Corporation Tax registration process, HMRC gives you the option to register for PAYE and VAT simultaneously. Whether you should depends on your circumstances — VAT is only mandatory above the £90,000 turnover threshold, and PAYE is only required if you are paying salaries.

What if I miss the three-month registration deadline?

Register as soon as you realise you have missed it. HMRC does not impose a separate penalty purely for late registration, but late registration almost always leads to a late CT600 filing and late payment — both of which carry automatic penalties and interest. The longer you delay, the larger the bill.

Is a business bank account legally required for Corporation Tax?

No. A business bank account is not legally required for a UK limited company. However, it is practically essential for accurate Corporation Tax computation — mixing personal and business transactions makes bookkeeping difficult, increases accountancy costs, and raises red flags if HMRC conducts an enquiry.