PROBLEM TO BE SOLVED : To provide a proper premium calculating method providing the financial product of reverse mortgage involving no risk for a client.SOLUTION : This method comprises a step for estimating the time point of death of a virtual client in the future on a simulation, step for estimating interest to be applied to each of financing time points during a period to the settlement time point of the virtual client and interest to be applied to a period from each of financing time points and the settlement time point, step for estimating a real estate price at the settlement time point for each of clients, step for calculating the expected value of present value on the side of payment at the settlement time point, step for calculating an estimated settlement money at the settlement time point for each of clients, step for calculating the expected value of present value on the side of receiving by calculating the present value of a smaller amount between the estimated real estate price and the estimated settlement money, and step for performing calculation so that the expected value of the present value on the side of payment can be equal with the expected value of the present value on the side of receiving and determining a premium price on the basis of that calculation.