Deductions & credits

@zomboo  I would like to get your opinion on how I should calculate how much of my mortgage interest will be deductible in 2024.

My situation for 2024 is as follows:

1. Primary residence: My wife and I will live in our primary residence from 01 JAN - 04 JUN. Closing date is 04 JUN. Plan to rent Airbnb until the construction of our new home is complete. Secondary home will become primary home after sale.

2. Secondary residence: Construction loan used with variable loan draws starting 12 JAN 24. Anticipate completion of construction ~01 SEP. Upon completion, construction loan will be replaced with a conventional loan using a refinancing action which I intend to put down $400k at closing to reduce the final debt amount.

I used variables in place of the actual interest incurred since those values are not exactly known right now, but I figured you could use them to help convey how best to calculate the average balance for each loan and the estimated % I would be able to deduct. 

REQUEST: Can you please help me identify the best option(s) for calculating the average loan balance and the amount of mortgage interest I can deduct in the 2024 tax season?