This paper presents a general equilibrium monetary model in which infl
ation distorts a variety of marginal decisions. Although individually
none of the distortions is very large, they combine to yield substanti
al welfare cost estimates. A sustained 4 percent inflation like that e
xperienced in the US since 1983 costs the economy the equivalent of 0.
41 percent of output per year when currency is identified as the relev
ant definition of money and over 1 percent of output per year when M1
is defined as money. The results illustrate how the traditional, parti
al equilibrium approach can seriously underestimate the true cost of i
nflation.