I usually file jointly but for a variety of reason's, we're considering filing separately. I tried using the "what if" worksheet to see what the difference would be, but I'm confused about what it's doing. For most deductions, like gifts to charity, it just took whatever total I entered in the joint tax return that I filled out earlier and split it evenly between the two hypothetical separate returns, letting me adjust as needed if one or the other of us spent more on something. But for the mortgage interest, it's doing something different. It didn't take the number from the joint return but left the row blank. I want to split the mortgage interest relative to our income so I planned to enter $18K in for me and $11K for spouse to reflect an accurate split. However, if I enter $18K in for me, it autofills negative $18K for spouse with no option to edit. No matter what number I enter--even if I try to do a 50/50 split or enter a number that's low or higher than we actually paid, I end up with a negative number in my spouses column, giving them a negative net deduction and a huge tax bill for them. If I delete the mortgage interest all together, the tax bill is actually much lower, which makes no sense since it is set to itemize whether that number is there or not. Is this a glitch in the software or some weird tax math that I just don't understand. (Yes, I have double and triple checked that it is set to itemize).
