Homeowners who take out a 15-year mortgage have 15 years to pay it off in fixed, equal installments plus interest. A 30-year mortgage, on the other hand, provides borrowers with 30 years to pay off their loans. Your monthly payments will be lower with a 30-year mortgage because you'll have more time to pay off the debt. However, because interest is levied monthly, you'll pay more interest throughout the loan. You can reduce your interest costs with a 15-year mortgage, but your monthly payments will be greater.