Every UK limited company and LLP needs one small piece of information to file anything online with Companies House-yet it's one of the most commonly lost, misunderstood, and overlooked items in company administration. This guide covers everything you need to know about the Companies House authentication code, from where to find it and how to replace it, to keeping it secure and avoiding costly filing delays.
Key Takeaways
The Companies House authentication code is a unique six-character alphanumeric code assigned to your company. It works like a digital signature, confirming that whoever is filing online is authorised to update the company's details on the public register.
You cannot file online-whether that's a confirmation statement, annual accounts, or director changes-via the Companies House WebFiling service or other compatible software without this code.
New codes are always sent by post (never by email or phone) to the company's registered office address or, in some cases, to an officer's home address. Delivery can take up to 5–10 working days.
Treat the company authentication code with the same care as a bank card PIN: restrict access to trusted people, change it if compromised, and request a reminder well before any filing deadline.
How you obtain or recover the code depends on whether you incorporated directly with Companies House or through a company formation agent.
What is a Companies House authentication code?
A company authentication code is a six-character mix of letters and numbers (for example, A1B2C3) issued by Companies House to every limited company and LLP that uses online filing. The authentication code is a six-character alphanumeric identifier that is unique to your company-not to any individual person.
It acts as a digital signature for online filings at Companies House. When you enter it during an online submission, you are confirming that the filing is authorised by someone in control of the company. Without it, filings are typically rejected outright.
This code is completely different from your company number, and it is also different from personal identity verification codes issued to individual directors or people with significant control under the newer ECCTA rules. You may see it referred to as a "Companies House authentication code", "company authentication code", "WebFiling authentication code", or "Companies House online filing code"-they all mean the same thing.
The code works across Companies House WebFiling and other compatible e-filing software that connects to Companies House online.
How and when you receive your company authentication code
All new UK companies receive an authentication code automatically soon after incorporation. The authentication code is automatically generated when a company is formed, but how and when it reaches you depends on how the company was set up.
If you registered directly with Companies House, the code is printed on a letter posted to the company's registered office address. Companies House sends the code to the registered office address, and it usually arrives within 5 to 10 working days after company formation.
If a company formation agent handled the incorporation, they often receive the code on your behalf-sometimes electronically-and display it in the client's online dashboard or welcome documents. It's worth checking with your agent before assuming the code was never issued.
Companies House does not disclose authentication codes by email or over the phone for security reasons. Companies House sends authentication codes by post only, and any unsolicited contact claiming to share or "speed up" your code should be treated as suspicious.
If mail to the registered office is repeatedly returned undelivered, Companies House may change the authentication code and notify the company by post at the updated address.
Finding your company authentication code
Where you find the code depends on who formed the company and who currently manages company filings.
Formed by an agent: The code is usually stored in the agent's online portal, the initial incorporation email, or the PDF incorporation pack provided on the day of formation.
Formed directly with Companies House: Look for the original postal letter headed "Company authentication code" sent to the registered office after incorporation.
Filed by an accountant or third party: Accountants or other presenters who file documents on the company's behalf may also hold the code. However, the directors remain responsible for knowing where it is stored.
Because many companies only need the code once or twice a year, it's easy to misplace. Store your company authentication code securely-for example in a password manager-so it's accessible when you need it.
Requesting a new or reminder authentication code
If the code is lost, never arrived, or is held by someone no longer authorised to act on your behalf, you can easily request a fresh one from Companies House.
Here's the standard process:
Sign in to (or register for) the Companies House WebFiling service.
Select your company using your company number.
Choose the option to request an authentication code or request a reminder.
Existing companies can request a reminder of their authentication code through WebFiling at any time. The replacement code is posted to the company's registered office address and normally arrives within 5–10 working days, though delivery may be slower during busy periods.
If directors cannot access the registered office-for example, if an old agent or previous accountant controls that address-they can use the separate Companies House service that posts the code to an active company officer's home address.
You cannot file online until you receive the new code, so it is important to act quickly and request a new authentication code well in advance of any upcoming filing deadline. Companies House will not extend deadlines just because a code is in transit.
Request a reminder code as soon as you suspect the original is lost, rather than waiting until the night before a deadline.
Using your authentication code with Companies House online
The same authentication code is used each time you file online via Companies House WebFiling or compatible software for that specific company. You need the code to submit updates through the online system.
The most common filings that require the code include:
Filing type | Example |
|---|---|
Confirmation statement | CS01 |
Annual accounts | Dormant, micro, small, or full accounts |
Director/secretary changes | Appointments, resignations |
Registered office changes | Form AD01 |
PSC updates | People with significant control |
Some filings requiring the code are appointing directors and changing registered addresses. Submitting annual accounts also requires it. You must enter the exact six alphanumeric characters when prompted, and only the most recently issued code will work to authorise information filed online.
If you file via commercial software, you may also need a separate presenter ID and presenter authentication-these are different from the company's own authentication code.
A Government Gateway account (used for HMRC services like corporation tax returns) cannot be used to file information with Companies House. The company authentication code is still required for all Companies House online filing.
Changing or cancelling your company authentication code
You can change your authentication code online anytime using Companies House WebFiling or Companies House online services. Changing your code can prevent unauthorized access-especially if a former director, company secretary, or previous accountant still knows the old code.
Steps to change the code:
Sign in to Companies House WebFiling.
Choose your company from your account.
Confirm your existing code.
Select the option to change or cancel, then set a new 6-character alphanumeric code.
Choose a code that is memorable for authorised users but difficult to guess. Avoid obvious sequences, your company name, or easily associated dates.
Once a new code is confirmed, all previous company authentication codes become invalid immediately for online filing. The old code will no longer work. Companies House sends code change confirmations by letter to the registered office.
Remember to notify trusted third parties who file on the company's behalf-such as accountants or agents-whenever the code is changed or cancelled.
Security: keeping your company authentication code safe
Think of the authentication code like a bank card PIN: anyone who has it can attempt to change company details online. The authentication code should be treated like a PIN; anyone with it can alter company details online, so keeping it private is a serious security measure.
Best practices:
Limit access to current directors and authorised professionals only. The authentication code should only be shared with trusted individuals.
Never share the code by unsecured email, messaging apps, or plain-text documents.
Store the code in secure, access-controlled systems such as an encrypted password manager or a locked internal record. Avoid plain spreadsheets or printed notes pinned to a noticeboard.
Change your authentication code if someone unauthorized knows it.
If you suspect the code has been compromised or an ex-employee still knows it, change the code immediately and review recent filings for suspicious activity.
Companies House will never ask for your authentication code over the phone or by unsolicited email. Any such contact should be treated as potential fraud. For the same security reasons, they do not disclose codes via any channel other than post.
What if your registered office or formation agent has changed?
Problems often arise when a company changes its registered office, accountant, or company formation agent without updating Companies House or retrieving the authentication code first.
If the registered office on the public register is outdated, any new authentication code will be sent to the old address. This creates a risk of lost mail-or worse, the code landing in the wrong hands.
How to resolve it:
Update your registered office address if it's outdated before requesting a new code. You can file a change of registered office (Form AD01) using a paper form with a company officer's signature if the code is not available.
Once the new address is on record, request a replacement code, which will arrive at the updated registered office.
If a previous formation agent still holds the code, directors should either retrieve it formally or change the code via Companies House once they regain control of filings.
Keep the company's registered office address and officer details up to date at all times so that sensitive correspondence-like authentication codes-reaches the correct people promptly. This is especially important if you are transferring management away from a previous accountant or agent who is no longer authorised.
Impact on filing deadlines and company compliance
Your authentication code is directly tied to timely online filing and overall Companies House compliance. The authentication code is needed for online changes or mandatory filings-and losing it at the wrong moment can have real consequences.
Missing or losing the code shortly before the due date for annual accounts or the confirmation statement can cause delays that trigger automatic late filing penalties:
Delay (private company) | Penalty |
|---|---|
Up to 1 month | £150 |
1–3 months | £375 |
3–6 months | £750 |
Over 6 months | £1,500 |
Companies House does not extend deadlines because a replacement code is in transit. Persistent failure to file can ultimately result in compulsory strike off, removing the company from the register entirely.
To avoid delays:
Check well ahead of key dates that the code is known, accessible, and still valid.
Request a new authentication code where necessary with enough buffer time.
Build a simple internal compliance calendar that pairs each filing deadline with a check that the company authentication code is on hand and secure.
Frequently asked questions
Is my company authentication code unique to my company?
While the combination of company number plus authentication code is unique for filing purposes, similar or identical 6-character codes can technically exist across different companies. Security is maintained because Companies House always checks both the company number and that company's current authentication code together. Another company sharing the same 6-character sequence cannot file on your behalf because they do not have the matching company number and presenter credentials.
Can Companies House email or tell me my authentication code over the phone?
Companies House will not send the company authentication code by email and will not disclose it over the phone under any circumstances. Codes are always sent by post-either to the company's registered office address or, where the dedicated security service is used, to an active officer's home address. Treat any email, text message, or call promising to reveal or "speed up" your authentication code as a phishing or scam attempt. If in doubt, contact Companies House directly through their official channels.
How long does it take to get a new authentication code?
It can take up to 5 working days to receive the new code after making an online request, but Companies House advises allowing up to 10 working days, especially at busy periods of year. No online filing can be completed until the replacement code has been received and activated. Suggest requesting a reminder code as soon as you suspect the original is lost to avoid delays.
What should I do if someone files changes without my permission?
Log in to Companies House online services immediately, change the company authentication code, and review all recent filings for accuracy. Contact Companies House to report suspected fraudulent filings and follow any guidance provided on removing or correcting those entries. In serious cases, you may also wish to seek legal advice or report the matter to relevant authorities-especially if assets, shareholding, or control of the company appear to be at risk.
Do I need a separate authentication code for every company I run?
Each registered company or LLP has its own distinct 6-character Companies House authentication code tied to its specific company number. Directors who sit on multiple boards need to manage multiple codes-one per entity-in a secure and organised way. Using a structured password manager or central compliance record can reduce confusion and help ensure the correct code is used for each company when filing online. You cannot use the same authentication code across different companies, even if you are the sole director of all of them.
