Am I looking at mortgage interest deduction on primary home correctly?

[Eddie Torres]

I had question about the mortgage interest deduction on my primary home. I understand that I can deduct mortgage interest up to $750k on my personal residence. Let's say my 1st mortgage balance is $600k and I want to take out a 2nd mortgage for $150k for home improvements which makes the interest on the 2nd deductible as well. Obviously I want the lowest interest rate possible but the way I'm looking at it is that it doesn't make much difference (from a tax standpoint) if the interest rate on that 2nd mortgage is 6% or 9% since the mortgage interest is deductible. Either way, based on my personal taxes, the deduction of that interest ends up being a refund to me every year and gets put back into my pocket. Would you say I'm looking at it correctly? Or am I looking at it wrong?

My questions stems from wanting to take out a 2nd mortgage to build an ADU now while rates or high or keep waiting until rates drop. TIA.