Per IRS Publication 936:
Home mortgage interest. You can deduct home mortgage interest on the first $750,000 ($375,000 if married filing separately) of indebtedness. However, higher limitations ($1 million ($500,000 if married filing separately)) apply if you are deducting mortgage interest from indebtedness incurred before December 16, 2017.
The TaxAct® program does not calculate for mortgage interest that is larger than the deduction amount. You need to calculate your deductible mortgage interest and report it in box 1 on Form 1098 in the TaxAct program. To report Form 1098 in the TaxAct program, go to our Form 1098 - Entering in Program FAQ.
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