One mortage secured by 2 properties. First property is 64% of the loan, and a primary residence. The second is a rental. Do I split the interest and principal 64/34?

If the two properties are unrelated and the mortgage interest needs to be allocated between the two properties, you will need to do the calculations yourself. Enter the appropriate percentage for your rental and the rest for Schedule A. Enter the allocated mortgage balance for Schedule A only.

However, if this is an owner-occupied rental, enter Form 1098 on your rental property first. Be sure you have indicated that the rental portion is 36% of the property. In this situation, the mortgage balance (principal) is not entered. TurboTax will transfer the remaining 64% of the interest to your itemized deductions.