Fiscal sustainability is one of the most pressing policy issues of our time. Yet it remains difficult to quantify. Official debt is plagued with a number of measurement difficulties since its measurement reflects the choice of words, not policies. And forming the fiscal gap-the imbalance in the...

Every country faces what economists call an intertemporal (across time) budget constraint, which requires that its government's future expenditures, including the servicing of its outstanding official debt, be covered by its government's future receipts when measured in present value. The...