Sovereign Debt Sustainability and Central Bank Credibility

This article surveys the literature on sovereign debt sustainability from its origins in the mid-1980s to the present and focuses on four debates. First, we evaluate the shift from an accounting-based view of debt sustainability using government borrowing rates to a model-based view that uses stochastic discount rates. Second, we review empirical tests, focusing on the relationship between primary balances and debt. Third, we discuss debt sustainability in the presence of rollover risk. And fourth, we evaluate whether government borrowing costs below rates of growth (r < g) generate a free lunch, in the sense that debt sustainability does not require future primary surpluses. We argue that liquidity services provided by sovereign debt may indeed lead to a free lunch, albeit one of limited size. The value of such services depends on the credibility of the central bank, which can be accumulated via prudent policies and subsequently drawn on to allow for looser fiscal policy.