If you need to file information for a UK limited company online, one of the first things you may be asked for is your Companies House authentication code. It is a six-character code made up of letters and numbers and is used to authorise certain information filed online for a company. Companies House describes it as the equivalent of a company officer's signature, which is why it should be protected carefully.

For a new company owner, the process is straightforward: register for the Companies House online filing service, and Companies House posts the authentication code to the company's registered office address. It is not normally sent by email or given over the telephone. This guide explains exactly how to get your code, what to do if it does not arrive, how to replace a lost code, and how the authentication code differs from the newer Companies House personal code.

What Is a Companies House Authentication Code?

A Companies House authentication code is a company-specific security code used to authorise certain online filings. It is associated with the company, not with an individual director. Companies House says the code is a six-digit alphanumeric code and should be treated with the same care as a bank card PIN because someone who has it may be able to make changes to the company's details online.

You may need the code when using Companies House online services to file information such as company accounts or report changes to company details. For example, Companies House guidance for filing company accounts states that you need the email address and password used for the online service as well as the authentication code sent to the registered office.

The three things people often confuse

It is useful to distinguish:

• Company number: identifies the legal company.
• Authentication code: authorises certain online company filings.
• Personal code: identifies an individual who has completed Companies House identity verification.

They are not interchangeable.

How Do You Get a Companies House Authentication Code?

The basic process is:

1. Register for Companies House online filing.
2. Provide your email address.
3. Create a password.
4. Companies House sends the authentication code by post.
5. The code is sent to the company's registered office.
6. Use the code when completing eligible online filings.

Companies House says that if you are using its online filing service for the first time, you can register online and the authentication code will then be posted to your company's registered office address. For companies that already have an authentication code, Companies House can send a reminder rather than issuing a completely new code in some circumstances.

Step 1: Make sure your company is registered

You need a UK company for which Companies House maintains a register before you can obtain a company authentication code. For most entrepreneurs, this will be a private limited company. Your company will have a company number once incorporation has been completed. Do not confuse this number with the authentication code. Your company number is publicly searchable; the authentication code is a confidential security credential.

Step 2: Register for Companies House online filing

Go to the official Companies House online filing service and register using your email address and a password. Companies House states that you need an email address and password when registering for the service. You should use an email address that you control and check regularly.

If an accountant, company formation provider or another professional manages your company's filings, establish clearly who controls the online account and where important correspondence is being received.

Step 3: Wait for the authentication code to arrive

Companies House sends the authentication code by post to the company's registered office address. This is an important security measure. Companies House currently advises that delivery can take up to five days. It also states that, for security reasons, the authentication code cannot be provided by email or over the phone. So if you have just registered for online filing, do not expect an instant email containing your code.

Example

Suppose you incorporate: Greenfield Digital Ltd, You register for online filing on Monday. The authentication code is then posted to the company's registered office. If your registered office is operated by a company formation provider, the provider may receive the letter on your behalf depending on the service arrangement you have chosen. The important question is not simply "Did Companies House send it?" It is: "Who receives Companies House post at my registered office, and how will I get the letter?"

What If You Are Using a Registered Office Service?

This is particularly important for entrepreneurs who do not live in the UK. A company can have a UK registered office even when its directors or shareholders live overseas. If your registered office is provided by a formation agent or professional service provider, Companies House correspondence will go there. Before incorporating, confirm:

• Who receives physical mail?
• How quickly will letters be scanned or forwarded?
• Will you be notified when Companies House correspondence arrives?
• Who has access to your filing credentials?
• What happens if you change service providers?

For international founders, this administrative arrangement can be just as important as the incorporation itself. A company may be perfectly valid on the Companies House register while its owner is effectively unable to access important correspondence because nobody has established a reliable mail-handling process.

How Long Does It Take to Get the Companies House Authentication Code?

Companies House guidance states that you should allow up to five days for delivery of the authentication code. Because the code is sent by post, the timing can depend on the company's registered office arrangements and postal delivery. If you have been waiting longer than expected, first check:

1. The registered office address on the Companies House register.
2. Whether the company has received other Companies House correspondence.
3. Whether your registered-office provider has received the letter.
4. Whether you registered for the correct online filing service.

Do not assume that the code was sent to your home address simply because you are the company's director.

What If Your Authentication Code Has Not Arrived?

If your code has not arrived, check the registered office first. This is often the simplest explanation.

Check your registered office address

Search your company on the Companies House register and confirm that the registered office address is correct. If the address is wrong, you should deal with that issue through the appropriate Companies House process. Companies House makes clear that changes to company information can be filed online, although the authentication code may be required for the online process.

Ask your registered-office provider

If another company receives mail on your behalf, contact them. Ask whether they have received a Companies House letter containing the authentication code.

Don't ask Companies House to email it

Companies House specifically states that the authentication code cannot be provided by email or telephone for security reasons. That means an email request such as "Please send me my authentication code" is not the normal process.

What If You Lost Your Companies House Authentication Code?

Losing the code does not mean you need to form another company. Companies House provides processes for companies that already have an authentication code and need to access or use the online filing service. When you use the online filing service, Companies House can send a reminder where the company already has a code.

If you cannot access the code, follow the official Companies House instructions rather than attempting to guess it or obtain it from an unofficial website. For security reasons, do not assume that an accountant, formation agent or third-party website claiming to "recover" your code is legitimate.

Can You Get the Authentication Code by Email?

Normally, no. Companies House posts the authentication code to the company's registered office. Its online filing guidance specifically states that, for security reasons, the code cannot be provided by email or telephone.

This distinction is important because scammers sometimes use fake Companies House emails to collect sensitive information. Companies House warns that it will never call you asking for your authentication code, password or bank details.

Can an Accountant Get Your Companies House Authentication Code?

An accountant or other professional may manage Companies House filings for your company if you have authorised them to act for you. However, there is an important distinction between giving a professional permission to handle a filing and giving your security credentials to an unknown third party. If your accountant requests the authentication code, verify:

• Who you are dealing with
• What filing they are preparing
• Why the code is required
• Whether they are authorised to act for the company
• How the code will be stored

Companies House has also introduced Authorised Corporate Service Providers (ACSPs). These can include accountants, solicitors and company formation agents that meet the relevant requirements and can carry out specified Companies House services. For founders using a company formation or management platform such as IncorpUK, it is worth understanding which filings are handled on your behalf and which company credentials remain under your control.

Is the Companies House Authentication Code the Same as the Personal Code?

No. This is one of the most important distinctions for company directors in 2026. The authentication code belongs to the company and is used to authorise certain online filings. The Companies House personal code belongs to an individual who has completed identity verification. Companies House identity verification became a legal requirement from 18 November 2025, with implementation being phased over a 12-month transition period.

Once an individual successfully verifies their identity, Companies House issues a unique personal code. That personal code is then used to connect the person's verified identity with their role in a company.

Simple comparison

A director may therefore need to manage both codes.

Do New Directors Need a Personal Code?

Yes, under the new identity-verification framework, directors have identity-verification obligations. Companies House says that when registering a new company, the personal code for each director must be provided as part of the registration filing. Existing directors must provide their personal code with the company's next confirmation statement during the transition period. This is separate from obtaining the company's authentication code. For example, someone incorporating a UK company in 2026 may need to deal with:

• Company incorporation
• Director identity verification
• Personal code
• Company authentication code
• Online filing account
• Annual confirmation statement
• Annual accounts
• HMRC tax registration and filings

These are separate administrative requirements.

How to Keep Your Authentication Code Safe

Companies House recommends treating the authentication code with the same care as a bank card PIN. That is a useful standard.

Do:

• Store the code securely.
• Limit access to people who genuinely need it.
• Keep track of professionals authorised to file for the company.
• Make sure your registered office receives official correspondence.
• Monitor your Companies House record.

Don't:

• Publish the code online.
• Put it on your website.
• Send it to random people.
• Give it to someone who contacts you unexpectedly.
• Assume an email claiming to be from Companies House is genuine.

Companies House specifically warns about scams designed to obtain authentication codes. It advises that genuine Companies House emails come from addresses ending in .gov.uk and recommends reporting suspicious emails rather than clicking links or sharing information.

What Can Someone Do With Your Authentication Code?

The code is significant because it can be used to authorise online filings. Companies House says that anyone who knows the code can change company details online, which is why it recommends protecting the code like a bank PIN. That makes security particularly important for:

• Sole directors
• Family businesses
• Startups with multiple founders
• Overseas company owners
• Companies using external accountants
• Businesses changing professional advisers

If you suspect that your authentication code has been compromised, do not ignore it. Review the company's Companies House record and follow Companies House guidance for protecting the company and dealing with unauthorised changes. Companies House also provides the PROOF scheme, a free service designed to protect participating companies from certain unauthorised paper filings.

A Practical Checklist for New UK Company Owners

Once your company has been incorporated, use this checklist:

Company setup

• Confirm your company number.
• Confirm the registered office address.
• Confirm who receives physical Companies House mail.
• Register for online filing.
• Receive the authentication code.
• Store it securely.

Identity verification

• Complete Companies House identity verification when required.
• Obtain your personal code.
• Understand when your personal code must be provided for each company role.

Ongoing administration

• Keep company details accurate.
• File accounts on time.
• File confirmation statements on time.
• Report relevant changes to Companies House.
• Keep track of Companies House correspondence.
• Review the public company record periodically.

This simple system prevents the authentication code from becoming an afterthought.

Frequently Asked Questions

How do I get a Companies House authentication code?

Register for the Companies House online filing service. Companies House will post the authentication code to your company's registered office address. Delivery can take up to five days.

Can I get my Companies House authentication code online?

You can register for the online filing service online, but the authentication code itself is normally sent by post to the company's registered office. Companies House does not provide the code by email or telephone for security reasons.

How long does a Companies House authentication code take?

Companies House advises allowing up to five days for delivery.

Where is the authentication code sent?

It is sent to the company's registered office address.

What should I do if my authentication code does not arrive?

Check the company's registered office address and ask whoever receives mail there whether the letter has arrived. If necessary, use the official Companies House process for obtaining or reminding the authentication code.

Can my accountant use my authentication code?

An accountant can handle company filings if properly authorised to act for you. Before sharing sensitive credentials, confirm the accountant's identity, authority and the specific filing being handled.

Is the authentication code the same as my Companies House personal code?

No. The authentication code belongs to the company and is used for certain online filings. The personal code belongs to an individual who has completed Companies House identity verification.

Can Companies House give me the authentication code over the phone?

No. Companies House states that the authentication code cannot be provided by telephone or email for security reasons.

What happens if someone steals my authentication code?

Because the code can authorise online changes, you should treat a compromised code seriously. Monitor the company's Companies House record and contact Companies House through its official channels if you suspect unauthorised activity.

Do overseas founders need a Companies House authentication code?

Yes, if they need to use the relevant online filing services for their UK company. Living outside the UK does not remove the company's need to maintain proper Companies House filing arrangements.

Conclusion

Getting a Companies House authentication code is straightforward, but it is important to understand the process. For most companies, you register for online filing and Companies House posts the code to the company's registered office. Allow up to five days for delivery, and remember that the code is not normally provided by email or telephone.

The most important thing after receiving it is security. Your authentication code is effectively a company-level signing credential, not another piece of information to publish alongside your company number. And with Companies House identity verification now being phased into the UK's company administration system, do not confuse your company authentication code with your personal identity-verification code. They serve different purposes and may both be relevant to directors and business owners.

For founders, particularly those operating a UK company from overseas, the best approach is simple: establish who controls your registered office, who receives official correspondence, who is authorised to file for the company, and where sensitive credentials are securely stored. That small amount of organisation can save considerable trouble later.