The empirical literature on public debt and growth typically relies on the debt-to-GDP ratio, placing debt quantities at the centre of the analysis. Recent sovereign debt theory, however, emphasizes that sustainability also depends on debt-servicing costs and the economy's capacity to absorb government liabilities. This paper therefore examines whether alternative dimensions of debt sustainability better identify the fiscal stress regimes associated with the debt-growth relationship. Using semiparametric threshold models with endogenous threshold variables and regressors, we compare the debt-to-GDP ratio with interest payments relative to GDP and debt relative to stock-market capitalization, and further examine interest payments relative to debt and debt relative to tax revenue as alternative financing and fiscal-capacity indicators […]