This paper identifies how a rise in the deficit/debt impacts interest rates by looking at the high-frequency response of interest rates to fiscal surprises. The fiscal surprises are the unexpected components of deficit releases and the changes in official forecasts by the Congressional Budget Office and by the Office of Management and Budget. The paper estimates that a rise in the deficit-to-GDP ratio of 1 percentage point raises the 10-year nominal rate by 8.1 basis points. This is quantitatively similar for other Treasury maturities and for corporate debt interest rates. The paper also investigates which of the theoretical channels is driving this relationship and whether surprises are affecting interest rate expectations or the term premium. These results are used to estimate how recent spending proposals may affect interest rates.