In this study, the prospective buyers were defined to be the families who plan to purchase houses in the coming few years, 5 years for instance. For those who were able to afford the expected house is referred as the ”prospected demand”. We empirically measured the housing affordability according to two economic conditions: (1) the down payment constraint according to family wealth accumulated, and (2) the credit constraint to pay the mortgage loan according to annual family income. The price of the expected house was estimated via a hedonic approach on the study area. We measure the affordability at individual level so that the difference of socioeconomic characteristics and different preferences across families would be captured. We computed the elasticity of the percentage change of the prospected demand with respected to the policy change of mortgage interest rate. The results can be applied to evaluate the effects of housing policies, for example, the mortgage interest subsidization.