I have two mortgages, one purchased prior to Dec 2017, and another purchased last May. In the, "Do any of these situations apply to you?" section, I answer no because in my case, each loan is below the limit of $1M and $750K respectively. Yet TurboTax doesn't seem to know about subtracting the prior debt from the $750K limit and incorrectly (I think) allows me to deduct the interest from both mortgages fully. I've checked the Schedule A line item and all the interest is there.
