Quoted: Some of the money may be overseas. Less than a quarter of U.S. currency resides abroad, estimates University of Wisconsin economist Edgar Feige. Where?s the rest? Legitimate business owners and those without bank accounts rely heavily on cash. And some is hidden away by the real-life equivalents of Breaking Bad?s Walter White in an underground ?cash only? economy. The U.S. may lose more than $100 billion a year in taxes on unreported income of over $400 billion, according to the Tufts study and others.