People's childbearing intentions change over the course of their reproductive lives. these changes have been conceptualized as occurring in response to the realization that an individual is unlikely to achieve his or her intended fertility, because of constraints such as the “biological clock” or lack of a partner. in this article we fnd that changes to child-bearing plans are infuenced by a much wider range of factors than this. People change their plans in response to the wishes of their partners, in response to social norms, as the result of repartnering, and as the result of learning about the costs and benefts of parenthood; there are also differences between the factors that infuence men's and women's decisionmaking. in a departure from existing studies in this area, we use a fexible analytical framework that enables us to analyze increases in planned fertility separately from decreases. this allows us to uncover several complexities of the decisionmaking process that would otherwise be hidden, and leads us to conclude that the determinants of increases in planned fertility are not simply equal and opposite to the determinants of decreases.