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The rest of the world holds a great deal of U.S. currency, i.e., cash. Although the amount can’t be precisely tracked, the Federal Reserve Board of Governors recently estimated that foreigners held $950 billion in U.S. banknotes at the end of the first quarter of 2021, or about 45% of all Federal Reserve notes outstanding, including two-thirds of all $100 bills. Overall holdings of U.S. currency have grown rapidly, however, and overseas holdings of Federal Reserve notes would now be worth closer to $1.1 trillion if such holdings are still half of all U.S. currency.
From: The Innocent Greenbacks Abroad: U.S. Currency Held Internationally.
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The U.S. currency supply has increased rapidly in recent years to about $2.28 trillion in September 2022.4 If 45% of that is held abroad, foreigners are currently giving the U.S. government an interest-free loan of $1.03 trillion each year.