Federal Debt Held by Federal Reserve Banks as Percent of Gross Domestic Product (HBFRGDQ188S) (https://fred.stlouisfed.org/series/HBFRGDQ188S) was first constructed by the Federal Reserve Bank of St. Louis in October 2012. It is calculated using Federal Debt Held by Federal Reserve Banks (FDHBFRBN) (https://fred.stlouisfed.org/series/FDHBFRBN) and Gross Domestic Product, 1 Decimal (GDP) (https://fred.stlouisfed.org/series/GDP): HBFRGDQ188S = (FDHBFRBN/GDP)*100