One object of the present invention is to provide a method for determining the current value and future value of customers who purchase specific merchandise, and the resources thereof, in order to provide data by which to select effective sales-promotion investments suitable for such customers, and for predicting sales according to the target and conditions of the investments. A sales-predicting method that classifies customers are into customer-value cells that determine the magnitude of current and future customer value and resources for future customer value, based on purchase data for specific merchandise and using three axes, including a purchase-amount index (first axis), a user-type index (second axis), and a customer-purchase-relevance index (third axis), and that measures changes in the customer-asset cells over time and changes due to sales-promotion investments, and that simulates sales by quantifying causal relationships between sales-promotion investments and sales.