Mortgage interest is the cost you pay to borrow money from a lender to buy a home. When you take out a mortgage, the lender charges you interest on the amount you borrow, which is typically expressed as a percentage. This interest is added to your monthly payments, along with the principal amount, which is the original loan amount. The interest rate can vary based on factors like your credit score, the type of mortgage, and current market conditions. Over time, as you make payments, a portion goes toward reducing the principal, while another portion covers the interest.