We develop a new methodology to compute differences in the expected longevity of individuals who are in different socioeconomic groups at age 50. We deal with two main problems associated with the standard use of life expectancy: that people’s socioeconomic characteristics evolve over time and that there is a time trend that reduces mortality over time. Using HRS data for individuals from different cohorts, we estimate a hazard model for survival with time-varying stochastic endogenous covariates that yields the desired expected durations. We uncover an enormous amount of heterogeneity in expected longevities between individuals in different socioeconomic groups, albeit less than implied by a naive (static) use of socioeconomic characteristics. Our analysis allows us to decompose the longevity differentials into differences in health at age 50, differences in mortality conditional on health, and differences in the evolution of health with age. Remarkably, it is the latter that is the most important for most socioeconomic characteristics. For instance, education and wealth are health protecting but have little impact on two-year mortality rates conditional on health. Finally, we document an increasing time trend of all these differentials in the period 1992–2008, and a likely increase in the socioeconomic gradient in mortality rates in the near future. The mortality differences that we find have huge welfare implications that dwarf the differences in consumption accruing to people in different socioeconomic groups.