On a $400,000 loan, for example, a buyer who made only minimum payments over the first five years would add more than $27,000 to the end of the loan, assuming short-term rates increase by one percentage point over the course of the loan, said Robert Binette, a mortgage broker with Hamilton Mortgage in Ridgefield, Conn. The monthly payment would jump from $1,718 in the final month of the fifth year to $2,580 after the loan was reset, a difference of more than 50 percent.