Who determines how much interest is paid on the national debt?
No one. Interest is the price of credit and, as in any competitive market, prices are determined by supply and demand. The Federal Reserve — the nation's central bank — auctions the securities on behalf of the U.S. Treasury. The securities go to the highest bidders.
SOURCE: Federal Reserve Bank of New York
National Debt Glossary
Looks up the key terms for understanding America's financial crisis