I have a client who sold his personal residence in Illinois in 2022. The mortgage on that home was $300,000 at the time he sold it. 

After selling the IL home, he bought a home in Idaho and took out a $950,000 mortgage. He is splitting this loan with his son and each will deduct their half of the mortgage interest. Both are on the deed and both on the loan, and each makes their 50% payment each month.

How do I apply the $750K mortgage limit in this situation?

Any help would be appreciated!