We present a decision-support tool that will assist engineers with the design of thermoplastic parts for improved dimensional stability. The tool addresses performance issues that cause significant deformation of the plastic part during its life cycle and thus changes in critical dimensions. The degradation of dimensional stability has a direct influence on the quality of the part and its cost is estimated by applying the Taguchi Loss Function. In this way, the quality cost can be combined with the manufactured cost of the part for a total part cost. The tool helps estimate these manufacturing and quality costs early in the product-development process where changes can be made relatively easily. In this paper we present the design analysis process of the tool, a description of the software, and a case study of its use in an industrial application.