Federal Debt Held by Private Investors as Percent of Gross Domestic Product (HBPIGDQ188S) (https://fred.stlouisfed.org/series/HBPIGDQ188S) was first constructed by the Federal Reserve Bank of St. Louis in October 2012. It is calculated using Federal Debt Held by Private Investors (FDHBPIN) (https://fred.stlouisfed.org/series/FDHBPIN) and Gross Domestic Product, 1 Decimal (GDP) (https://fred.stlouisfed.org/series/GDP): HBPIGDQ188S = (FDHBPIN/GDP)*100