A mortgage buydown involves paying an up-front charge to obtain either a temporary of permanent lower rate on a new mortgage. . For example, a mortgage lender may be offering a standard 30-year mortgage at 4.0 percent with a 1 percent origination fee. The lender may allow you to buy the mortgage rate down to 3.50 percent by paying an additional one percent buydown fee. All mortgage lenders will offer the ability to buy down a mortgage interest rate. The cost of the buydown percentages will vary.