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Why does sustained money growth cause inflation but not long-run real growth?

Topic 5.3 Money Growth and Inflation: apply the quantity theory of money and the equation of exchange to explain why sustained money growth raises the price level in the long run.

A focused answer to AP Macroeconomics Topic 5.3, covering the quantity theory of money, the equation of exchange, the long-run neutrality of money, and why sustained money growth causes inflation rather than real growth, with full worked calculations.

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  1. What this topic is asking
  2. The equation of exchange
  3. The quantity theory of money
  4. The long-run neutrality of money
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What this topic is asking

Topic 5.3 explains the long-run link between money growth and inflation. The College Board wants you to use the equation of exchange and the quantity theory of money to show that, in the long run, sustained money growth raises the price level rather than real output, because money is neutral in the long run.

The equation of exchange

The quantity theory of money

The quantity theory makes two simplifying assumptions: velocity is roughly stable, and in the long run real output is fixed at potential (set by resources and technology, the vertical LRAS). Writing the equation of exchange in growth rates:

The long-run neutrality of money

In the short run, monetary policy does affect real output (because of sticky wages), but in the long run only the price level moves. This is the same lesson as the vertical long-run Phillips curve and the vertical long-run aggregate supply curve seen from a third angle: demand-side stimulus, including money creation, cannot raise real output permanently. It also explains the classic AP result that a central bank which repeatedly expands the money supply to chase lower unemployment ends up with persistently higher inflation and unemployment back at its natural rate. Hyperinflations, where money growth runs to hundreds or thousands of percent, are the extreme illustration: the price level tracks the money supply almost exactly, because real output cannot keep pace with the printing press.

Try this

Q1. State the equation of exchange. [1 point]

  • Cue. M×V=P×YM \times V = P \times Y.

Q2. Money grows 5%, velocity is stable, real output grows 2%. What is long-run inflation? [2 points]

  • Cue. %ΔP=5%−2%=3%\%\Delta P = 5\% - 2\% = 3\%.

Exam-style practice questions

Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

AP 2018 (style)1 marksMultiple choice. According to the quantity theory of money, if the money supply grows by 6% a year, velocity is constant, and real output grows by 2% a year, the long-run inflation rate will be approximately (A) 2%. (B) 3%. (C) 4%. (D) 6%. (E) 8%.
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The answer is (C). The equation of exchange in growth-rate form is %ΔM+%ΔV=%ΔP+%ΔY\%\Delta M + \%\Delta V = \%\Delta P + \%\Delta Y. With %ΔV=0\%\Delta V = 0, inflation %ΔP=%ΔM−%ΔY=6%−2%=4%\%\Delta P = \%\Delta M - \%\Delta Y = 6\% - 2\% = 4\%.

(D) ignores real growth. (A) reports real growth, not inflation. (B) and (E) miscompute. Subtracting real growth from money growth gives 4%, so (C).

AP 2021 (style)4 marksFree response. (a) State the equation of exchange. (b) Explain the meaning of velocity. (c) The money supply grows by 8% a year, velocity is stable, and real output grows by 3% a year. Calculate the long-run inflation rate. (d) Explain why this sustained money growth raises prices rather than real output in the long run.
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A 4-point calculation FRQ.

(a) Equation (1 point): M×V=P×YM \times V = P \times Y, where M is the money supply, V is velocity, P is the price level, and Y is real output.

(b) Velocity (1 point): velocity is the average number of times a unit of money is spent on final goods and services in a period.

(c) Inflation (1 point): in growth rates, %ΔP=%ΔM+%ΔV−%ΔY=8%+0%−3%=5%\%\Delta P = \%\Delta M + \%\Delta V - \%\Delta Y = 8\% + 0\% - 3\% = 5\%.

(d) Reasoning (1 point): in the long run the economy is at full employment, so real output is fixed by resources and technology; extra money cannot raise real output and instead bids up prices (money is neutral in the long run).

Markers reward the equation of exchange, the velocity definition, the 5% inflation rate, and the long-run-neutrality reasoning.

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