Consideration of postnatal population-based genetic screening programs is becoming increasingly common. Assessing the medical and psychosocial impacts of this can be particularly complex for genetic conditions with variable phenotypes, especially when outcomes may be more related to quality of life rather than reducing physical morbidity and mortality. In this article, we present a framework for assessing these impacts, by comparing diagnosis and non-diagnosis at different age points. We use the example of Klinefelter syndrome, a common yet frequently under-diagnosed genetic condition for which interventions are available. This framework can be used to supplement established screening guidelines and inform decision-making.