I was having the same issue and couldn't understand why TurboTax was entering a negative number in the Mortgage Interest field. After an hour with tech support (who was great,) I finally realized that I was checking the boxes for my 1st and 2nd mortgages that says "Yes, include for this home office deduction." However, since I am taking the standard deduction, I should not check those. (Says so right above the boxes.) I was then entering the combined amount again under "Excess Mortgage Interest" a few pages later, where it says to do so if you are not itemizing deductions (taking the standard deduction.) It must have been subtracting it twice and causing the negative number. I started to notice that when I was experimenting with entering round figures for my mortgage interest (e.g. $10,000) and saw that it was deducting the combined amount from the two figures. (I didn't do all the math, but that's what tipped me off.) Hope this helps someone!
