Several programs associating financial gains with the achievement of weight loss objectives have been set up over the last decade. These programs seem to produce mixed effects, possibly because their designs differ both in terms of the objectives assigned to the participants and the amounts awarded in case of success. In this article, we examine whether these programs should – contrary to what they usually offer – be tailored to the characteristics and the preferences of the subjects. Our theoretical model suggests that participants are more likely to lose weight if the difficulty of the goal assigned to them and the reward they obtain in the event of success are jointly defined according to their preferences towards risk.