This paper examines the effects of demographic dynamics on the measured rates of economic growth. First, it develops a model of production with labor productivity that varies with age. Second, it uses macroeconomic and demographic data to estimate the relative productivity of different age groups. Third, it constructs a panel database of effective labor supply in order to reflect the changing age-structure of the population. Fourth, it decomposes the historical measured growth rates into effects of demographic dynamics and into “real” growth rates, net of demographic effects.