When you take out a buydown mortgage, you are paying a lump sum at the beginning of your mortgage in order to pay a lower interest rate for a specified term at the beginning of your mortgage. The period that you will be paying a lower interest rate is usually from 1 to 3 years. For the remainder of the mortgage term, you would pay the full interest amount. Many times, the buydown can be funded by the seller or by the lender, so the expense would not come out of your pocket.