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Quantity theory of money (MV = PQ)
Fisher 1911; roots in 1500s· Theory or school
Mainstream viewMost economists and practitioners agree.
The quantity theory says more money chasing the same goods raises prices over time: money times velocity equals prices times output.
See it on the Money & Finance map →How it works
MV = PQ is an identity: money (M) times how often each dollar is spent per year (velocity, V) equals the price level (P) times real output (Q). The theory adds a claim: if velocity and output are fairly stable, faster money growth mainly raises prices. Copernicus sketched the idea in the 1520s, and Jean Bodin used it in 1568 to explain inflation from New World silver. Irving Fisher formalized it in 1911; Milton Friedman revived it as monetarism.
Why it matters
It underlies the rule that printing money to pay bills ends in inflation. Friedman's line: inflation is 'always and everywhere a monetary phenomenon'.
Facts, rules and data
It holds well across countries and decades, especially in high inflation. It fit poorly in the 2010s, when QE ballooned bank reserves but inflation stayed low.
Debates and risks
Velocity proved unstable after the 1980s, so in 1993 the Fed downgraded money growth as a policy guide. How much M2's 2020–22 surge caused the inflation that followed is debated.
Connections (4)
▸Quantity theory of money (MV = PQ) is the core of Monetarism and Milton FriedmanMainstream view
The connection
Monetarism takes the MV = PQ identity and adds a bet: if velocity (V) is fairly stable, faster money growth (M) mainly raises nominal spending and, over time, prices (P). Friedman turned that into policy: grow money at a steady few percent a year, and inflation stays low.
When and why
Irving Fisher stated the equation in 1911; Milton Friedman restated it as a theory of money demand in 1956 and built monetarism on it at the University of Chicago.
How solid is the link?
Friedman's 1956 essay 'The Quantity Theory of Money: A Restatement' explicitly presents his approach as the old theory updated; the lineage is undisputed.
Debates and risks
Velocity swung widely after 1980 and again during QE in the 2010s, so whether money growth predicts inflation closely enough to guide policy is debated.
▸Quantity theory of money (MV = PQ) depends on stable Velocity of moneyExperts disagree
The connection
MV = PQ is true by definition; it becomes a theory of inflation only if velocity (V) is stable. Then more money (M) must mean more spending, and eventually higher prices (P). When velocity began swinging widely in the 1980s, the link between money growth and inflation weakened sharply.
When and why
Irving Fisher, 1911; Milton Friedman and Anna Schwartz argued in 1963 that velocity was predictable. M1 velocity broke from trend in the early 1980s, M2's around 1990.
How solid is the link?
St. Louis Fed velocity data show relative stability before about 1990 and large swings since, including a long fall during 2008–2020.
Debates and risks
The 2020–21 money surge, followed by inflation, reopened the debate over whether velocity is stable enough for money growth to predict prices.
▸Quantity theory of money (MV = PQ) links money growth to Inflation: rising prices, shrinking purchasing powerMainstream view
The connection
If money grows faster than the goods and services it buys, and spending habits (velocity) hold steady, prices must rise. The theory predicts that long-run inflation roughly equals money growth minus real output growth.
When and why
Jean Bodin, explaining silver-driven price rises in 1568; Irving Fisher in 1911; Friedman and Schwartz in 1963.
How solid is the link?
Cross-country data over decades show a strong money-inflation link, especially when inflation is high; year to year in low-inflation economies, the link is weak.
Debates and risks
Whether the 2020–22 jump in M2 caused the inflation, or both came from the same stimulus and supply shocks, is debated.
▸Weimar Germany hyperinflation (1923) is cited as proof of Quantity theory of money (MV = PQ)Mainstream view
The connection
Germany's money stock exploded as the Reichsbank printed to cover war debts, reparations and support for strikers in the occupied Ruhr. Prices rose even faster than money, because people spent marks immediately, raising velocity. Monetarists cite it as the textbook case of money growth driving prices.
When and why
Germany, 1921–23; prices rose about 29,500% in October 1923 alone. It ended with the Rentenmark in November 1923.
How solid is the link?
Reichsbank money and price records, analyzed by Phillip Cagan (1956) and Thomas Sargent (1982), among others.
Debates and risks
Some historians stress reparations and the balance of payments as root causes, with printing a symptom; Sargent stressed fiscal reform in ending it.