CT600 for year to 2024

Thanks for getting in touch.

I've checked your account and can confirm your payment went through successfully - you have an active Solo Unlimited subscription and do not need to make another payment.

The reason your CT600 hasn't been submitted is that the company authentication code you entered doesn't match what HMRC has on file. Each time you tried to submit, HMRC returned an authentication failure (Error 1046).

To resolve this:

1. Check your authentication code - This is a 6-character code from HMRC (not the same as your Companies House authentication code). It would have been sent by post when the company was first registered for Corporation Tax.

2. If you can't find it, you can request a new code from HMRC:

- Call HMRC on 0300 200 3410

- Or request online via your HMRC Business Tax Account

- A new code typically arrives within 7 working days

3. Once you have the correct code, go back to your CT600 form on TinyTax, enter the correct authentication code, and click Submit.

Also note: Your accounts for the year ending 30 April 2025 are due at Companies House on 31 January 2026 (in 2 days), so you may want to file those soon too.