Companies House Auth Codes

Find your Companies House Authentication Code for filing accounts. Learn where to locate it, how to request a new one, and fix common auth code errors.

To file accounts with Companies House through TinyTax, you need your company's Authentication Code. This guide explains what it is, where to find it, and how to fix common issues.

What is an Authentication Code?

The Authentication Code (also called "auth code" or "company authentication code") is a 6-character alphanumeric code unique to your company. It proves you're authorised to file on behalf of that company.

ℹ Each company has its own unique auth code. If you have multiple companies, you need a separate code for each one.

Where to Find Your Auth Code

If You've Filed Before

When you first registered your company, Companies House sent an auth code by post to your registered office address. If you've filed online before, you've used this code.

Check:

  • Previous emails or documents from your accountant
  • Your company records or filing folder
  • Previous TinyTax submissions (we save it securely for you)

Request a New Code

If you can't find your code, request a new one from Companies House:

  1. Go to gov.uk/file-your-company-annual-accounts
  2. Click Request an authentication code
  3. Enter your company number
  4. Confirm your registered office address
⚠ New codes are sent by post to your registered office. They typically arrive within 5 working days.

Using Your Auth Code in TinyTax

When you click Submit Accounts on the preview page, a modal appears asking for your Authentication Code:

Enter your 6-character alphanumeric code (e.g., ABC123). This is the code sent to your registered office by Companies House.

ℹ TinyTax saves your auth code securely for future submissions, so you only need to enter it once per company.

Common Auth Code Errors

"Invalid Authentication Code"

This means the code you entered doesn't match what Companies House has on file.

Check:

  • You're using the code for this specific company (not another company you manage)
  • You've entered all 6 characters correctly
  • The code hasn't expired

"Authentication Code Expired"

Auth codes expire 28 days after being issued. If you requested a new code and didn't use it within 28 days, you'll need to request another.

"Company Not Found"

This usually means there's a mismatch between your company details and what Companies House has on file.

Check:

  • Your company number is correct
  • Your company hasn't been struck off or dissolved
  • You're filing for the right company

Auth Codes for Different Company Types

Company TypeAuth Code Required?
Private Limited (Ltd)Yes
Public Limited (PLC)Yes
Limited by Guarantee (CLG)Yes
LLPYes (different system)
CICYes (but TinyTax can't file CIC accounts)
⚠ Community Interest Companies (CICs) require additional reporting that TinyTax doesn't support. You'll need to file CIC accounts directly with Companies House.

Security Best Practices

Your auth code is like a password for your company. Keep it secure:

  • Don't share it publicly - Anyone with your auth code could file on your behalf
  • Store it securely - Keep it in a password manager or secure filing system
  • Request a new one if compromised - If you think someone else has your code
ℹ TinyTax encrypts your auth code when storing it. We never display the full code after you've entered it.

Requesting a New Auth Code

You can request a new auth code at any time. The new code will:

  • Be sent to your registered office address
  • Automatically invalidate any previous codes
  • Take about 5 working days to arrive
To request:
  1. Visit gov.uk/file-your-company-annual-accounts
  2. Click Request an authentication code
  3. Enter your company number
  4. Confirm the registered office address
⚠ If your registered office address has changed, update it with Companies House first. Auth codes are always sent to the registered office.

Frequently Asked Questions

"Can I use the same auth code for multiple filings?"

Yes! Your auth code remains valid for all filings until you request a new one. TinyTax saves it securely so you don't need to re-enter it each time.

"I've moved offices - will my auth code still work?"

Yes, but:

  • Your existing code remains valid
  • If you need a new code, update your registered office address first
  • New codes go to the current registered office

"My accountant has my auth code - can I still use TinyTax?"

Yes. Your accountant should be able to share the auth code with you. It's your company's code, not theirs. If they're reluctant, you can request a new one.

"How do I know if my auth code is still valid?"

Unfortunately, there's no way to check without trying to use it. If it's been more than 28 days since you requested it and you haven't used it, it may have expired.

When you submit through TinyTax, you'll immediately find out if the code is valid.

"Can I file accounts without an auth code?"

No. The auth code is mandatory for all electronic filings to Companies House. Paper filings (which TinyTax doesn't support) use different authentication methods.

Still Having Issues?

If you've tried the troubleshooting steps above and still can't submit:

  1. Check Companies House directly - Log into the WebFiling service to verify your account status
  2. Request a new code - It's the quickest solution for most auth code issues
  3. Contact us - We can help diagnose the specific error

Last updated: December 2025

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