As a product is manufactured, it is subject to multiple sources of variation. Manufacturers use tolerance stack-up analysis to predict how often the accumulated variation of individual parts will compromise the functionality of the final product. Our goal is to create a model in Microsoft Excel that uses Monte Carlo methods to simulate these variations and provide information about the potential feasibility of a product. With these results, engineers can make necessary changes to the production or assembly process. We are developing such a model in Excel to make conducting simulation and tolerance stack-up analysis affordable and broadly accessible