Here's the evidence from Tim Sablik in "Is Cash Still King?" written for Econ Focus from the Federal Reserve Bank of Richmond (Second Quarter 2018, pp. 18-21). Back in the 1990s and into the first decade of the 2000s, $1 bills were most common, with $20s in second place. (This ranking accurately represents my own wallet, for what it's worth!). But $100s have growth steadily and taken over first place.
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Indeed, the total value of US currency in circulation has been rising over time, but most of that gain in value is due to the rise in $100 bills.
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Clearly, there is a puzzle here. As Sablik points out, evidence from consumer surveys finds that cash is used for about 27% of transactions in the last decade or so, but mostly for small purchases. It seems unlikely that the number of $100 bills in circulation is about typical consumers making typical purchases. In round numbers, the 12 billion $100 bills in circulation divided by a US population of 325 million implies that on average, every person in the US has 37 $100 bills in their possession. The total amount of US cash in circulation works out to about $4,800 for every person in the US. (This does not accurately represent the contents of my wallet.)
The standard explanation is that a considerable amount of US currency is being used outside the US, both as a medium of exchange and as a store of value. Some proportion of that amount--no one really knows how much--is surely helping to facilitate illegal activities. There are ongoing proposals to eliminate large-denomination bills: Sablik points out that the European Union ended production of 500-euro notes in 2016.
For some previous posts on the subject, see:
- "Eliminate High-Denomination Bills?" (March 18, 2016)
- "Who is Holding the Large Denomination Bills? (August 11, 2014)
- "The Soaring Number of $100 Bills" (June 10, 2013)