Federal Debt Held by Agencies & Trusts as Percent of Gross Domestic Product (HBATGDQ188S) was first constructed by the Federal Reserve Bank of St. Louis in October 2012. It is calculated using Federal Debt Held by Agencies & Trusts (FDHBATN) and Gross Domestic Product, 1 Decimal (GDP): HBATGDQ188S = ((FDHBATN/1000)/GDP)*100 FDHBATN/1000 transforms FDHBATN from millions of dollars to billions of dollars.