The Tax Cuts and Jobs Act of 2017 (TCJA) reduced the federal income tax mortgage interest deduction from the amount of interest paid on $1,000,000 of debt to interest paid on $750,000 of debt. If your mortgage originated on or before December 15, 2017, it falls under the higher pre-TCJA limit. If it originated later, then it falls under the lower limit of the TCJA. The exception is if you refinance a mortgage after December 15, 2017 that originated before that date. In this case, as long as you only refinance the remaining balance or less, the higher pre-TCJA limit applies to the refinanced mortgage.