We document the cumulative effect of four decades of income growth below the growth of per capita gross national income and estimate that aggregate income for the population below the 90th percentile over this time period would have been $2.5 trillion (67 percent) higher in 2018 had income growth since 1975 remained as equitable as it was in the first two post-War decades. From 1975 to 2018, the difference between the aggregate taxable income for those below the 90th percentile and the equitable growth counterfactual totals $47 trillion.