Dart, a triangle-shaped folded and stitched tuck in a garment, is a common sewing technique used to provide custom-fit garments. Unfortunately, designing and optimally placing these darts requires knowledge and practice, making it challenging for novice users. We propose a novel computational dart design framework that takes rough user cues (the region where the dart will be inserted) and computes the optimal dart configurations to improve fitness. To be more specific, our framework utilizes the body-garment relationship to quantify the fitting using a novel energy composed of three geometric terms: 1) closeness term encoding the proximity between the garment and the target body, 2) stretchability term favouring area-preserving cloth deformation, and 3) smoothness term promoting an unwrinkled and unfolded garment. We evaluate these three geometric terms via off-the-shelf cloth simulation and use it to optimize the dart configuration by minimizing the energy. As demonstrated by our results, our method is able to automatically generate darts to improve fitness for various garment designs and a wide range of body shapes, including animals. CCS CONCEPTS • Computing methodologies → Computer graphics.