How high can government debt rise before it becomes unsustainable?
Core argument: Sustainable net debt limits across the US and 24 other OECD countries average 234% of GDP under historical interest rate–growth differentials and 221% for the US, falling to 214% on average and 186% for the US under current, higher interest rates and growth.
Using historical, current, and dynamic interest rate-to-economic growth differentials, countries’ sustainable debt limits are calculated on a net of central bank holdings of government debt basis. Sustainable net debt limits average 234% of GDP for these countries assuming historical rates and economic growth (221% for the US), 214% assuming (higher) current interest rates and economic growth (186% for the US). If, however, interest rates were to rise systematically with debt according to conservative assumptions, there is no model solution for France, Greece, Japan, Italy, the UK, and the US, given their current high debt levels; the average sustainable limit is 178% for the other countries. A reasonable conclusion to draw for the US is that the fiscal path under current policy and trends with rising interest rates is not sustainable in the short to intermediate term. A major fiscal consolidation package will be needed soon, as interest rates rise, unless significantly higher inflation or capital controls will result.




