Every economy faces a "fiscal limit" that delivers the maximum government debt-GDP ratio that can be sustained without appreciable risk of default or higher inflation. But governments in advanced economies issue substantial nominal debt and nominal debt is a commitment to repay in nominal units. When such economies are approaching their fiscal limits, debt can be devalued through higher current and future inflation rates. The paper develops a simple bond market supply-demand apparatus to explain how fiscal policy can be a source of inflation, while monetary policy merely determines the timing of inflation.