Abstract The diversity of early family life courses is thought to have increased, although empirical evidence is mixed. Less standardized family formation is attributed to compositional changes in educational attainment, labour market participation, and childhood living conditions. I investigate whether and why family trajectories have become more or less standardized across birth cohorts in Sweden. I combine sequence metrics with Oaxaca–Blinder decompositions to assess the compositional shifts that drive changes in family formation standardization. Family trajectories of individuals born in 1952, 1962, and 1972 from age 18 to 35 are reconstructed using Swedish register data. My results demonstrate that early family formation has become more standardized across birth cohorts. Further, compositional differences between birth cohorts partially account for this standardization, especially for women. For example, higher levels of educational attainment are associated with family formation standardization. This substantiates arguments that family formation may re-standardize following the second demographic transition.