Companies House authentication code: where to find or request it

Companies House only6 charactersWhere you see it: Filing credentials › Companies House › Authentication code

Before entering figures, the filing setup questions can set the existing destination and CT600 route for an ordinary limited company. They keep the full accounts dates beside the CT600 dates. You can also continue with the controls below without opening the questions.

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What the code is

The code belongs to the company, not to you as a director. Companies House describes it as a 6 digit alphanumeric code, a mix of letters and numbers, and says it is the equivalent of a company officer's signature for information filed online. It is separate from your Government Gateway sign-in and your company's Corporation Tax UTR.

You need the code to file information online with Companies House or through filing software. It is not needed when you file only a Corporation Tax return with HMRC. Companies House also says you cannot use a Government Gateway account to send it information online.

How to request it

1. Sign in to Companies House WebFiling, or create an account if you do not already have one.
2. Follow the steps to request an authentication code for the company.
3. Companies House posts the code to the registered office. If the company already has a code, it sends a reminder instead.

Companies House says this can take up to 10 working days. If you cannot access the registered office address, it can send the code to your home address instead. Companies House cannot send the code by email or tell you it over the phone.

The official Companies House guidance on authentication codes has the current request and replacement process.

It is not your personal code

Companies House also issues a personal code to individuals when they verify their identity. That personal code identifies a person. It is different from the company authentication code used to file annual accounts for a company. Do not enter your personal code in Authentication code.

Common mistake: the wrong code

The dialog only checks the length. Fewer than 6 characters keeps the Submit button grey and shows Authentication code must be 6 characters, with how many you entered. Any 6 characters can be submitted, so a personal code, an old code that was changed, or a code with O typed for 0 reaches Companies House and is refused. Your accounts are then not filed. If Companies House rejects the code

Worked example

Company

Hornbeam Example Ltd

Accounts period

1 March 2025 to 31 May 2026 (15 months)

Destinations

Companies House and HMRC both ticked in the filing dialog

Where the director found the code

In the letter Companies House posted to the registered office

What was sent

One set of accounts to Companies House with the code, and two CT600s to HMRC with the Government Gateway details

The company and all figures on this page are fictional.

Using it to file accounts

1. Company Profile & Period

   What are you filing?

   Companies House or Companies House & HMRC CT600This sets which targets start ticked in the filing dialog. You can still change them there.

   More help: Choose Companies House, HMRC or both

2. Review & file

   Continue

   Click Continue to submission

3. Filing credentials

   Filing targets

   Companies House ticked

   Authentication code

   The 6-character code from Companies HouseLower-case letters are changed to capitals.

   Corporation Tax UTR

   Only if HMRC is ticked tooWhere to find your UTR

   Select the director submitting this return

   The director submitting the filing

   Accounts approval date

   The date the board approved the accountsAccounts approval date

   Declaration

   Tick it

   Click Submit to Companies House, or Submit to HMRC & Companies House if HMRC is ticked too.

When you approve the accounts and select Submit, the platform sends them to Companies House. Support staff do not file them manually. The code field starts empty each time the dialog opens, so you enter it for every filing.

Read how to choose Companies House, HMRC, or both if you only need to send one part of your annual filing.

Accounts longer than 12 months

When your accounts period ends more than 12 months after it starts, even by one day, HMRC needs two CT600s but Companies House receives one set of accounts for the whole period. You enter the authentication code once, and the filing page shows one Companies House row. The two CT600s go to HMRC with your Government Gateway details, which are separate from this code. How the dates are split

Sample outcome

If Companies House says your code is invalid

Your accounts have not been filed with Companies House. Check that you entered the current six-character company authentication code. A personal Companies House code or WebFiling password will not work here. If the company code has been changed, use the new one. Check similar-looking characters, such as O and 0.

1. Open your filing page and choose Re-file accounts →. On the company page the button is Re-file Accounts.
2. The Review & file page opens with only Companies House selected, so the CT600 is not sent again. Click Continue to submission.
3. Enter the current company code under Authentication code in the filing dialog.
4. Review the filing and submit it again. There is no extra charge to retry.

If you do not have the code, follow the request steps above or use the Companies House guidance. Delivery can take up to 10 working days. If you cannot access the registered office, Companies House can send the code to your home address. Your accounts deadline does not change because a code was rejected. Companies House can charge a late filing penalty when accounts are filed late.

Keep it safe

Companies House says to treat the code with the same care as your bank card PIN, because anyone who knows it can change your company's details online. Only share it with someone you trust to file for your company. If you think someone you do not trust knows it, sign in to Companies House WebFiling to change it. Anyone else who files for the company then needs the new code, because the old one stops working.

More help: Companies House: changing or cancelling your code · Companies House: looking after your code

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Official sources

• Companies House: company authentication codes for online filing
• Companies House WebFiling
• Companies House: late filing penalties