Maximizing return on investment in corn production is a balance of providing the lowest effective levels of inputs compared to projected returns. Weed control is an input that growers have numerous options to customize a program that fits weed spectrum, application timing, and most importantly cost. One variable that is critical in making herbicide decisions is the degree of risk associated with various herbicide programs. WeedSOFT is a computer program that assists growers in predicting yield loss and economic returns of herbicide programs based on the competitive loads of the weed species present. The competitive load (CL) of a weed species integrates a weed’s density (D) and its competitive ability (CI). In a field crop, a weed’s competitive ability is adjusted based on its size relative to the crop and becomes the adjusted competitive index (ACI). Then the CL is calculated as: CL=Dbi x ACIi. Total competitive load (TCL) is the sum of all the weed species present and is calculated as: TCL = Σ(Dbi x ACIi). This TLC plus the length of weed competition is used in WeedSOFT to predict crop yield loss.