New estimates of overseas U.S. currency holdings, the Underground economy and the "Tax Gap"

This paper examines the ‘currency enigma” which arises because despite financial innovation that has created important new substitutes for cash usage, U.S. per capita currency holdings now amount to $2700. American households and businesses admit to holding only 15 percent of the stock of currency outside of the banking system. Some fraction of unaccounted for currency is held overseas (the dollarization hypothesis) and some is held domestically undeclared, as a store of value and a medium of exchange for transactions involving the production and distribution of illegal goods and services, and for transactions involving incomes that are not reported to the IRS (the underground economy hypothesis). We first revisit the longstanding controversy concerning the fraction of U.S. currency held abroad and find that newly revised estimates of U.S. overseas currency stocks estimates the fraction overseas at 37 percent, rather than the widely cited figure of 65 percent. A more refined proxy places the fraction abroad closer to 30 percent. New estimates of overseas holdings permit calculation of domestic currency holdings, as well as narrow and broad measures of domestic monetary aggregates. These are tested to determine their ability to predict fluctuations in real output and prices. The domestic currency figures are then used to estimate the current amount of “unreported income” which approaches $2 trillion, implying a “tax gap” in 2008 of between $446- $490 billion.