Quicken Loans' Smart30 is a 30-year fixed-rate mortgage with an interest-only payment choice. It gives a low payment and interest rate up-front and security against rising interest rates. The interest-only choice allows customers to lower monthly payments when they choose to pay only the interest portion of monthly payments. As with any interest-only loan, when customers pay down the principal, the following month's interest-only payment goes down as well. The more principal the customer pays, the lesser the interest they owe the bank, which results in a lower monthly payment. Smart30 is available for Jumbo Loans as well.