Adding Corporation Tax to your Government Gateway is a one-time setup you need to do before you can submit a CT600 through TinyTax (or any other software):
1. Log in at gov.uk/log-in-register-hmrc-online-services — make sure it's an Organisation account, not an Individual account. Corporation Tax can only be added to an Organisation account.
2. Once logged in, select 'Add a tax, duty or scheme' and choose 'Corporation Tax'.
3. You'll need your company UTR (10 digits — HMRC sends this to your registered office shortly after incorporation) and your company registration number.
4. HMRC will post an activation code to your company's registered address. This usually takes 7–10 working days.
5. When the code arrives, log back in and enter it. Corporation Tax will then appear as an active service in your Gateway.
After that, you can enter your 12-character Gateway User ID and password in TinyTax when you reach the submission step — no separate connection step is needed.
If Corporation Tax is already listed in your Gateway services but you're getting an authentication error when submitting, that's a different issue — let us know with more detail and we'll help.
Full step-by-step guide: tinytax.co.uk/support/government-gateway-issues
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1. Log in at gov.uk/log-in-register-hmrc-online-services — make sure it's an Organisation account, not an Individual account. Corporation Tax can only be added to an Organisation account.
2. Once logged in, select 'Add a tax, duty or scheme' and choose 'Corporation Tax'.
3. You'll need your company UTR (10 digits — HMRC sends this to your registered office shortly after incorporation) and your company registration number.
4. HMRC will post an activation code to your company's registered address. This usually takes 7–10 working days.
5. When the code arrives, log back in and enter it. Corporation Tax will then appear as an active service in your Gateway.
After that, you can enter your 12-character Gateway User ID and password in TinyTax when you reach the submission step — no separate connection step is needed.
If Corporation Tax is already listed in your Gateway services but you're getting an authentication error when submitting, that's a different issue — let us know with more detail and we'll help.
Full step-by-step guide: tinytax.co.uk/support/government-gateway-issues