I estimated the impact on GDP of America’s recent and projected debt increase (in which the explosive growth of public spending on pensions and health care looms largest), using four alternative estimates of the effect of debt on growth: a smaller Reinhart/Rogoff estimate from a more recent paper; a widely used International Monetary Fund study, which finds a larger impact (and which deals with the potential reverse-causality problem); a related CBO study; and a simple production function with government debt crowding out tangible capital.