Modernized Austrian capital theory implies: in capital market equilibrium without public debt the average period of production equals the average waiting period of households. In the twenty-first century and for the OECD plus China area, demographic and production parameters are such that capital market equilibrium implies a negative real rate of interest. Price stability implies a non-negative real rate of interest. Prosperity requires capital market equilibrium. Thus, positive public debt is required for price stability under conditions of prosperity. Some conclusions are drawn for actual international macropolicy.