How much cash should you carry? A lot more than you think

How much cash do you carry? How often do you hit the ATM? Are your habits the most efficient? If you carry less than $500, the answer is no.

You may be surprised to learn that this question has generated a great deal of debate among economists. One way of approaching the question was by applying the Baumol-Tobin model of cash management, which takes into account several variables.

Professor Greg Mankiw ran the model for a person who spends $10 a day of cash, earns $60 an hour, takes 10 minutes per ATM visit, and makes 5% annual interest on his bank account. For this person, the model shows that this person should take out $1,200 three times a year, carrying an average balance in his wallet of $600. Much of this surprisingly high number is a function of the value of this person's time.

In 1995, Mankiw calculated that even the average American would be better off carrying an average of $551.05, when in fact the average citizen carried around $75.