First, the facts: on a $100,000 30-year mortgage at 6.5%, you'll pay $127,544 in interest, plus the $100,000 principal, for a total of $227,544. Paying one-half of your regular monthly mortgage every two weeks will result in interest of $97,215, a savings of $30,329. You'd have to earn over $42,000 before taxes to net that much money.