Deductible home mortgage calculation

Hi,

I got a mortgage that was over $750,000. Given that I can only deduct interest on the first $750,000 but I made extra principal payments taking it under $750,000, I wonder about the calculation.

Originally, in January, I owed over $800,000 but then I made an extra principal payment taking it under $750,000. This means that all the interest paid starting March (and some part of February) could be deducted?

Does TurboTax have any way of handling extra principal payments (I know the date I made the extra principal payment taking it under $750,000 but that doesn't show on form 1098). Will TT just do $750,000/original which would give a lower percentage?

Thanks!

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