The following is from the IRS instructions for Schedule A for 2018 (page A-8).
"Limit on loans taken out after December 15, 2017. For qualifying debt taken out after December 15, 2017, you can only deduct home mortgage interest on up to $750,000 ($375,000 if you are married filing separately) of that debt. If you also have qualifying debt subject to the $1,000,000 limitation discussed under Limit on loans taken out on or before December 15, 2017, earlier, the $750,000 limit for debt taken out on or after December 15, 2017, is reduced by the amount of your qualifying debt subject to the $1,000,000 limit."
