Reductions in women's labour supply after childbirth remain a persistent driver of gender earnings inequality. Using data from West Germany from the 1960s to 2013, this column explores the evolution of the ‘child penalty’ – post-birth earnings reductions for mothers – in Germany. The child penalty increased over time because women are earning more, so the opportunity cost of motherhood has grown. Family policies can affect gender inequality through changing post-birth earnings decisions. Future research should examine how policies influence pre-birth choices and interact with gender norms over the long run.