Traditional IRA Basis Tracking

yes looks like things went wrong in 2023 when it didn't carry over your basis from 2022.  But also the calculations for the Roth conversion in 2023 look off which is why you can't get Line 14 to zero; if it had the wrong basis to begin with then you would have also been taxed on the Roth conversion as it thought you only had a 6500 basis on a 12500+INT conversion.  What's on the other lines 6-13 for the 8606 in 2023?

For 2024, there should be an interview question where you provide the basis for line 2, it will default to the 2023 value if you did a carry over of the 2023 return but you should be able to edit it.  If you go back thru the questions under Deductions & Credits for Non-deductible IRA there's a question "yes I made and tracked nondeductible contributions to my IRA" and then "lets find your IRA Basis" and you should be able to update the amount there.  Did you go through that or is not working?

without the right basis, the calculations on the Roth conversion for 2024 will be wrong (same for 2023).  Line 5 seems ok to have the same (incorrect) value as Line, it's just Line 3 plus any contributions in Q1 2025.

Seems like you'll need to file amended return for 2023 with the revised 8606 once you get it fixed?

Not a CPA/Expert, just my 2 cents.

btw, the response to this post had a recap of the steps to enter a backdoor Roth so you can check all the steps and inputs you need to hit

https://ttlc.intuit.com/community/taxes/discussion/turbotax-incorrectly-showing-penalty-for-my-backdoor-roth-ira-contribution/00/3571512

also this article

https://ttlc.intuit.com/turbotax-support/en-us/help-article/retirement-benefits/enter-backdoor-roth-ira-conversion/L7gGPjKVY_US_en_US?uid=m8bipag3