The motivations to have children can be related to three main areas: biological predispositions, social pressure, and rational choice. The rational-choice approach to fertility assumes that individuals derive utility from having children (e.g., Becker 1981): decisions about fertility are therefore based on the net utility gains achieved by having children. In order to test the rational-choice approach to fertility, this paper investigates the relationship between parenthood and well-being, using a large sample of individuals from 94 countries throughout the world. We find that, controlling for a number of socio-economic and demographic characteristics, parenthood is negatively related to subjective well-being. The results are robust to a number of alternative empirical specifications and to the use of different indicators of well-being. Overall, the findings indicate that, on the basis of a purely economic approach, the optimal number of children for a rational agent is zero.