Economic Lot Sizes with Seasonal Demand

The simplest economic lot size formula containing only carrying costs and ordering costs is here extended to include the case of seasonal demand. Shortages and uncertainty are not allowed. The key step is the fitting of an analytical function to the seasonal demand pattern by means of harmonic analysis. This requires the demand to be specified as that consumed during N discrete and equal time periods. This function can then be manipulated to obtain the average inventories and optimum ordering times for the N possible ordering patterns using a graphical method of solution. The lowest-cost ordering pattern can then be determined by comparing the costs of the N ordering patterns. Limitations to the method are noted.