Mortgage interest is any interest you pay on a loan secured by a main home or second home. These loans include: A mortgage to buy your home; A second mortgage; A line of credit; A home equity loan; If the loan is not a secured debt on your home, it is considered a personal loan, and the interest you pay usually isn't deductible. Your home mortgage must be secured by your main home or a second home. You can't deduct interest on a mortgage for a third home, a fourth home, etc.