PUB 936 is poorly written because it doesn't cover your situation which is quite common. using example 1 in the pub as a basis (the 180K second mortgage proceeds use d to improve house taken out 3/2/2022 monthly balance 1,800,000 (180K X 10) average balance $150K 1.8M/12
i would say your average balance is $480K*10/12 + $1.1M * 5/12 which is about $858K
so your deduction would be 750/858 times the total of the interest
