In any given period the debt stock grows by the existing debt stock (d) multiplied by r-g, less the primary budget balance (p).

ECONOMIST: Daily chart

G. and Bain, stock price was not a useful benchmark of anything in the nineteen-seventies, because the market was stagnant.

NEWYORKER: Money Pol

The simple r-g assumption is one of the most important in debt dynamics: an r-g of greater than zero (when interest rates are greater than GDP growth) means that the debt stock increases over time.

ECONOMIST: Daily chart