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Go back and fix an error in CT600 inputs?
I have completed the numbers for a CT600 submission, but did not see how to include a capital allowance (AIA) claim. The report is now ready to submit, but I want to go back and add the AIA claim. How do I do this, please?
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To add your AIA claim:
1. Click Edit Form on the Review & Submit page.
2. Navigate to the Tax Computation step — you can use the section navigation at the top of the form to jump there directly rather than clicking through each page.
3. In the Tax Computation section, find the Annual Investment Allowance row and enter the full cost of the qualifying assets you want to claim.
4. Click Save & Continue through the remaining steps back to Review & Submit.
TinyTax will regenerate your CT600 and computations automatically with the AIA deduction included. The updated figures will appear in the refreshed documents on Review & Submit before you submit.
What you are seeing as 'Resubmit' is actually the Submit Corporation Tax to HMRC button, which is there ready for when you are done editing. Nothing has been sent.
To get back into the form and add your AIA claim:
1. Scroll down on the page you are on — below the document previews, there is an Edit Form button. It may not be visible at first glance if you are looking near the top of the page.
2. If you cannot find it there, go back to your Dashboard, find SKIPPER SOLUTIONS LTD, and click Continue Filing next to the 2024/25 period. That takes you to the same Review & Submit page with an Edit Form button at the bottom.
3. Once in the form, go to the Tax Computation section and find the Less: Annual Investment Allowance row. Enter your AIA claim there — for example, the full cost of the equipment purchased during the period.
4. Click Save & Continue through to the end and your documents will regenerate automatically with the updated figures.
5. Back on Review & Submit, check the tax figure looks correct, then click Submit Corporation Tax to HMRC.
For more detail on what qualifies and how the AIA works, see: https://tinytax.co.uk/support/capital-allowances-aia
You have two ways to get back into the form and add your AIA claim.
**Option 1 — direct link to your form (quickest):**
https://tinytax.co.uk/submission-form.php?prefill=FS_20260506163323_6f0d2f28
That drops you straight into the multi-step form with every figure already filled in.
**Option 2 — via the dashboard:**
1. On the dashboard, click the **Review Error ▾** button next to SKIPPER SOLUTIONS LTD.
2. Choose **View CT600 Error**. A panel opens explaining the 1046 error.
3. In that panel, click **Update Credentials & Retry**. That takes you to your Review & Submit page.
4. Scroll to the bottom — below the document previews you will see the **Edit Form** button.
**Adding the AIA claim:**
1. Once in the form, use the section navigation at the top to jump to **Tax Computation**.
2. Find the **Less: Annual Investment Allowance** row and enter the full cost of the qualifying plant/equipment you want to claim against this period profit.
3. Click **Save & Continue** through to the end. TinyTax automatically regenerates your CT600 and computations with the new figure.
**About the 1046 error itself:**
Error 1046 means HMRC did not accept the Government Gateway credentials TinyTax sent. As this is your first filing for SKIPPER SOLUTIONS LTD, the most common cause is that Corporation Tax is not yet enrolled on your Government Gateway account for this specific company. You can verify by signing into https://www.tax.service.gov.uk/business-account with the same User ID and password — if "Corporation Tax" is not listed, you will need to add it (HMRC posts an activation code, ~7-10 working days). Full walkthrough: https://tinytax.co.uk/support/hmrc-error-1046
Fix the AIA figure first — once your numbers are right, you can resubmit as soon as the Gateway enrolment is sorted.
We are also tracking a UX improvement on our side to surface an explicit Edit Form link in this error state, so future users do not get stuck the same way.