Fertilizer recommendations are typically given as the pounds of nitrogen, phosphorus, and potassium needed per acre. Many crop budgets also list the fertilizer costs in terms of the N, P, and K. This can cause a problem for farmers as they must purchase their fertilizer in products that in some cases contain multiple nutrients. These multinutrient fertilizers make it difficult or impossible to calculate a price per unit of a nutrient. Thus, finding the minimum cost fertilizer combination by using a price per nutrient approach may not work. This paper shows how a linear programming approach will always give the minimum cost fertilizer combination and then shows how a decision aid is developed in Excel. The developed decision aid has many uses in extension services where farmers have little understanding of linear programming. The decision aid is also useful in helping farm management students learn about linear programming.