We project that the outer-bound debt-to-GDP ratio that the U.S. economy can sustain is about 210 percent of GDP. Above this level, there is no feasible future additional tax on broad-based labor income that can finance the interest payments at the returns demanded by financial markets. The calendar year by which fiscal policy must change (the required “closure year”) varies significantly with a major future cost driver: healthcare excess cost growth. The required closure year is 2051 (25 years from now) under lower healthcare excess cost growth, 2048 (22 years) under medium excess cost growth, and 2045 (19 years) under higher excess cost growth consistent with historical values. Under the historical growth rate of healthcare costs, there is a 25% chance of hitting the debt maximum in 14 years. […]