Assuming the same interest rate for both loans, you will pay less in interest over the life of a 15-year loan than you would with a 30-year loan because you repay the principal at a faster rate. This also explains why the monthly payment for a 15-year loan is higher. Let’s say you get a 30-year mortgage at 6 percent on a $150,000 home. You will pay $899 a month in principal and interest charges. Over 30 years, you will pay $173,757 in interest alone. But a 15-year mortgage at the same rate will cost you less. You will pay $1,266 each month but only $77,841 in total interest—nearly $100,000 less.