Estimates of intergenerational mobility in lifetime income derived from incomplete income histories routinely incorporate in the estimation process, necessary life‐cycle adjustments to annual income data. The two‐stage method presented here first estimates proxies for fathers’ and sons’ lifetime family incomes from annual income observations, schooling and race; and then uses these income proxies to derive mobility measures. Applying this to United States PSID data for sons born between 1952 and 1981, we find a decline in intergenerational mobility in lifetime family income, as measured by the intergenerational elasticity of income, the rank‐rank correlation, absolute upward mobility, and other indicators.