Do primary deficits, not existing debt, drive the rising debt ratio?
Core argument: The annual change in the U.S. debt-to-GDP ratio equals the deficit plus a growth dividend, defined as last year's debt ratio times −y/(1+y), where y is the nominal GDP growth rate.
The deficit as a share of GDP increasingly exceeds each year’s change in the debt-to-GDP ratio. The debt ratio change equals the deficit plus the growth dividend: the amount by which GDP growth shrinks the debt ratio, equal to last year’s debt ratio times −y/1+y where y is the nominal GDP growth rate. The growth dividend has more than doubled since the Great Recession because the debt ratio has more than doubled. Adding a growth dividend row to CBO’s main budget table enables readers to exactly decompose America’s debt ratio path. Current debt increases the debt ratio each year by the amount that interest payments exceed the growth dividend. This excess interest remains negative in CBO baseline’s projection. Hence, America’s current debt is sustainable in the CBO baseline despite currently high interest payments. Projected primary deficits – i.e., future tax revenue failing to cover future non-interest spending – entirely drive America’s unsustainable debt ratio path. The primary deficit provides a good guide to how the debt ratio is projected to change, while the deficit does not.





