Under current law, the level of federal debt relative to gross domestic product (GDP) is projected to rise significantly over the next decade. The relationship between debt and interest rates plays a key role in the Congressional Budget Office’s economic and budget projections (especially long-term projections) and for dynamic analyses of fiscal policy, where the sensitivity of interest rates with respect to changes in the level of debt is vitally important. In this analysis, we use a reduced-form regression to estimate the relationship between projected federal debt and expected long-term interest rates. Our results suggest that the average long-run effect of debt on interest rates ranges from about 2 to 3 basis points for each increase of 1 percentage point in debt as a percentage of GDP. We also use a dynamic stochastic general equilibrium model to illustrate how the response of interest rates to debt depends on the type of fiscal policy generating changes in the debt. In the context of that model, fiscal policies that bolster incentives for households and firms to invest in private capital or supply additional labor elicit a smaller interest rate response than the response suggested by the reduced-form estimates, which do not control for the nature of the fiscal policy change. Conversely, the results suggest that a fiscal policy that contains few or no incentives for households and firms to invest in additional private capital or supply additional labor elicits a larger interest rate response than that suggested by the reduced-form estimates.