The present invention provides a method and a system for determining a promise date for a demand whose supply depends on constraints in a business environment. According to the present invention, information related to the business environment is stored within a data storage means. The present invention provides a processor coupled to the data storage means from which it requests and retrieves data. The processor also determines a plan date for each supply in the supply structure. The plan date is determined, from a highest level to a lowest level in the supply structure, based on existing and planned supply in the supply structure. After determining a plan date, the processor determines an available date for each supply in the supply structure. The available date is determined, from the lowest level to the highest level in the supply structure, based on the availability of each supply in the supply structure, and the plan date determined for each supply. Finally, the processor generates a promise date for the demand for the item based on each available date determined for a corresponding supply in the supply structure. The present invention advantageously generates promise dates based on information available in real-time on both the supply structure and the capacity constraints for a given item.