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short essays and reports on the economic issues of the day
2005 ■ Number 6

Wicksell’s Natural Rate
Richard G. Anderson
ost central banks now implement monetary policy by
setting a near-term target for an overnight interbank
interest rate. In turn, policymakers face the difficult
issue of how to choose, and adjust, the target rate. One widely
discussed policy guide is the “natural,” or equilibrium, real rate of
interest. To use this guide, one compares the level of a mediumterm financial-market real interest rate—such as the yield on a
10-year Treasury inflation-indexed bond—to an estimate of the
long-term “natural,” or equilibrium, rate of return on the economy’s
capital stock. The idea that inflation will be approximately constant
when these two rates of return are equal is an extension of an idea
advanced in 1898 by the Swedish economist Knut Wicksell.1
Wicksell, throughout his career, was an unwavering advocate
of the quantity theory of money. He argued that increases in the
economy’s average level of prices were due to excessive increases
in the monetary base, that is, increases beyond the increase in
the economy’s overall output. Precisely how this occurred, he felt,
was muddled in writings of the time. With the natural rate concept,
he sought to illuminate the transmission mechanism behind the
quantity theory and to begin connecting the monetary base,
banks’ extension of credit, aggregate demand, and inflation.
Wicksell based his theory on a comparison of the marginal
product of capital with the cost of borrowing money. If the money
rate of interest was below the natural rate of return on capital,
entrepreneurs would borrow at the money rate to purchase capital
(equipment and buildings), thereby increasing demand for all
types of resources and their prices; the converse would be true
if the money rate was greater than the natural rate of return on
capital. (Wicksell did not distinguish real from nominal interest
rates because, under the gold standard of the time, sustained
inflation was unlikely. Here, all interest rates and rates of return
should be interpreted as real rates.) So long as the money rate
of interest persisted below the natural rate of return on capital,
upward price pressures would continue. In Wicksell’s theory,
price pressure could arise even if new credit were extended only
against increases in production, that is, against “real bills.” Price
stability would result only when the money rate of interest and
the natural rate of return on capital—the marginal product of
capital—were equal.
Wicksell did not complete his theory of money, output, and
inflation. He did not propose a market mechanism that determined the money rate of interest. Nor did he advocate an activist


policy based on the natural rate for Sweden’s central bank, the
Riksbank. His work did, however, inspire later writers. John
Maynard Keynes took up Wicksell’s unfinished quest for a theory
connecting the price level to money and credit in his 1930 A
Treatise on Money.
Implementing monetary policy by means of a natural rate
framework has many uncertainties. The most relevant financial
market rates for household and firm behavior likely are not the
overnight rates set by central banks, but rather are intermediaterun rates of 5 to 10 years to maturity. Shocks to the economy,
such as an energy or financial crisis, may cause near-term real
rates of return on capital to deviate significantly from the longerterm rate of return on capital. Further, the natural rate is not
observable. It varies with the economy’s underlying ability to
produce, and must be estimated from empirical models often
subject to substantial disagreement. Beyond differences in structure, models depend on assumed long-run projections for variables such as productivity growth, the share of national income
received by capital, the aggregate savings rate from GDP, the
growth of the labor force, the rate of depreciation of capital, and
the variances and covariance of shocks to the economy. Agreement
among economists on these issues does not seem imminent.
Ironically, Wicksell’s work laid the foundations that have led
economists during the twentieth century to shift away from analysis of the quantity theory and, in some cases, to omit money
entirely from their models. But, models based on the natural rate
concept likely have some distance to go before they become useful guides to monetary policy. ■
Further reading: Angelo Mascaro, “Using the Natural Rate Concept to Assess the
Consistency of Projections Ten Years Ahead for Real Interest Rates and Inflation,”
Congressional Budget Office Technical Paper Series, number 2004-5, March 2004;
Thomas M. Humphrey, “Knut Wicksell and Gustav Cassel on the Cumulative
Process and the Price-Stabilizing Policy Rule,” Federal Reserve Bank of Richmond
Economic Quarterly, 88(3), Summer 2002; Roger W. Ferguson, Jr., “Equilibrium
Real Interest Rate: Theory and Application,” speech at the University of Connecticut
School of Business, October 29, 2004, available at

Wicksell introduced the natural rate in the 1898 paper, “The Influence of the
Rate of Interest on Commodity Prices,” reprinted in Erik Lindahl, ed., Selected
Papers on Economic Theory by Knut Wicksell (1958, pp. 67-92); it remains one
of the clearest expositions. He expanded the idea in Geldzins und Guterpreise
(1898), translated by R.F. Kahn as Interest and Prices (1936). The definitive
biography is Torsten Gårdlund, The Life of Knut Wicksell (1958).

Views expressed do not necessarily reflect official positions of the Federal Reserve System.