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HMRC submission fails / 13 month year ?
I am new to Tiny Tax
Submitting my first year of trding
Its a 13 month year
companies house submission went through ok, CT600 HMRC keeps failing
checked sign on for gov gateway - all coreect.
changed passwird, still fails
i note period that your system has split it so that period 1 (1st month only) is showing most of my turnover, this is incorrect, no revenue or transactions in period 1, all transactions and reveneue should be in period 2 (12 months from Aug 24 to july 25.
Please advise
Submitting my first year of trding
Its a 13 month year
companies house submission went through ok, CT600 HMRC keeps failing
checked sign on for gov gateway - all coreect.
changed passwird, still fails
i note period that your system has split it so that period 1 (1st month only) is showing most of my turnover, this is incorrect, no revenue or transactions in period 1, all transactions and reveneue should be in period 2 (12 months from Aug 24 to july 25.
Please advise
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About the period split
Your accounting period runs from 16 July 2024 to 31 July 2025, which is 12 months and 15 days. HMRC has a strict rule that no CT600 can cover more than 12 months, so TinyTax has automatically split it into:
CT600 Period 1: 16 July 2024 to 15 July 2025 (the first 12 months of trading)
CT600 Period 2: 16 July 2025 to 31 July 2025 (the remaining 15 days)
Period 1 is not "the first month" — it is the full first 12 months of your company's life. So the vast majority of your turnover correctly appearing in Period 1 is exactly right. Period 2 covers only the final 15 days of the accounting year, so it would naturally show very little revenue.
Your total figures are entered once and apportioned automatically across the two periods based on the number of days in each. You do not need to split anything manually.
More detail on how this works: https://tinytax.co.uk/support/extended-accounting-period
About the HMRC authentication failure (Error 1046)
Changing your password is unlikely to fix this. Error 1046 is a credentials authentication failure that almost always comes down to one of three causes:
1. Corporation Tax is not enrolled on your Government Gateway account. Even if you can sign in to the Gateway successfully, Corporation Tax needs to be listed as an active service in your Business Tax Account at https://www.tax.service.gov.uk/business-account — look for "Corporation Tax" in the list of services. If it is not there, you need to add it. HMRC will post an activation code to your company's registered address, which typically takes 7 working days. You cannot submit a CT600 online until you receive and use that code.
2. You are using the wrong Government Gateway account. The account you enter in TinyTax must be the one that holds the Corporation Tax enrolment for this specific company. The Government Gateway User ID is usually 12 digits (numbers only) — not your email address, not your HMRC online account number.
3. Temporary lockout from multiple failed attempts. After several failures in quick succession, HMRC can temporarily block further attempts. Wait at least an hour before trying again.
Since this is your first CT600 filing, cause 1 (CT not yet enrolled on the Gateway) is by far the most common reason. Check your Business Tax Account first to confirm Corporation Tax is listed as an active service before retrying the submission.
Full step-by-step guide: https://tinytax.co.uk/support/hmrc-error-1046