If you have to pay back a ACA subsidy overpayment then it's stated: "After all, it's impossible to know the future. It's normal for most people to overestimate or underestimate their ACA premium tax credit by a small amount. There's no added penalty for taking extra subsidies. The difference will be reflected in your tax payment or refund. So, you are not or will not be penalized for having underestimated you income a year earlier - however in Turbotax, they are taking what you owe in taxes (in my case which is under $1K) and then they add the ACA overpayment I owe (which now makes my total due over $1K) and therefore is calculating a penalty that I now owe. So, basically Turbotax is penalizing my ACA Subsidy Overpayment and this should not be the case!
