4.5 The Money Market

The money market shows how the demand for money and the supply of money set the equilibrium nominal interest rate. Money demand slopes downward because the opportunity cost of holding money is the interest you give up, while money supply is a vertical line set by the central bank.

Money Market Graph for AP Macro

On an AP Macro money market graph, the vertical axis is the nominal interest rate and the horizontal axis is the quantity of money. The money demand curve slopes downward, while the money supply curve is vertical because the central bank sets the monetary base.

Equilibrium is where money demand and money supply intersect. If money demand shifts right, the equilibrium nominal interest rate rises. If money supply shifts right, the equilibrium nominal interest rate falls. Most exam mistakes come from shifting the wrong curve or labeling the vertical axis as the real interest rate instead of the nominal interest rate.

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Why This Matters for the AP Macroeconomics Exam

The money market is one of the core graphs in the financial sector, and it connects directly to how monetary policy works. On the exam, you may be asked to draw the money market, show a shift caused by a change in the price level, real GDP, or central bank action, and explain how the nominal interest rate adjusts. Getting this graph right also sets you up for monetary policy questions, where a change in the nominal interest rate feeds into investment, consumption, and aggregate demand. Expect this model in both multiple-choice reasoning and free-response graphing and explanation.

Key Takeaways

• Money demand slopes downward because the opportunity cost of holding money is the nominal interest you could earn on bonds or other assets.
• Money supply is vertical because the central bank sets the monetary base, so the money supply does not respond to the nominal interest rate.
• Equilibrium happens at the nominal interest rate where quantity of money demanded equals quantity of money supplied.
• Money demand shifts from changes in the price level, real GDP, and transaction costs of spending money.
• Money supply shifts only from central bank monetary policy.
• A surplus of money pushes the nominal interest rate down, and a shortage pushes it up, until equilibrium is restored.

The Demand for Money

There is an inverse relationship between the nominal interest rate and the quantity of money people want to hold.

The reason comes down to opportunity cost. If you hold $100 as money (cash or a checking deposit), you give up the interest you could have earned by holding that $100 in bonds or other interest-bearing assets. That lost interest is the opportunity cost of holding money.

• When nominal interest rates are low, the opportunity cost of holding money is low, so people hold more money.
• When nominal interest rates are high, the opportunity cost of holding money is high, so people hold less money.

This is a movement along the money demand curve, not a shift. As the nominal interest rate falls, the quantity of money demanded rises, and as the nominal interest rate rises, the quantity of money demanded falls.

A quick reminder on rates:

• Nominal interest rate = real interest rate + expected inflation rate.

Shifters of the Demand for Money

Three things shift the entire money demand curve:

1. Price level
2. Real GDP
3. Transaction costs

A higher price level increases money demand because people need more money to make the same purchases at every nominal interest rate. The money demand curve shifts right, and the equilibrium nominal interest rate rises. A lower price level decreases money demand, shifting the curve left and lowering the equilibrium nominal interest rate.

An increase in real GDP raises money demand because there are more transactions happening in the economy, shifting money demand right. A decrease in real GDP lowers money demand, shifting it left.

Changes in transaction costs work the same way. If it becomes harder or more costly to turn other assets into money, people hold more money, increasing demand.

The Supply of Money

The monetary base is set by the country's central bank, which is the Federal Reserve in the United States. Because of this, the money supply is independent of the nominal interest rate, so the money supply curve is vertical.

The money supply stays fixed at whatever level the central bank sets, no matter the nominal interest rate. The way the money supply changes is through monetary policy. A change in monetary policy shifts the vertical money supply curve left or right, which changes the equilibrium nominal interest rate.

When the central bank uses monetary policy to increase or decrease the money supply, the goal is to move the nominal interest rate. A lower nominal interest rate encourages more investment and consumption, while a higher nominal interest rate discourages them. You will see how this plays out in monetary policy questions, but the money market is where that interest rate change starts.

Money Market Equilibrium

Money market equilibrium is the nominal interest rate at which the quantity of money demanded equals the quantity of money supplied. On the graph, the nominal interest rate is on the vertical axis and the quantity of money is on the horizontal axis.

Disequilibrium and How the Nominal Interest Rate Adjusts

If the nominal interest rate is above equilibrium, the quantity of money demanded is less than the quantity supplied, creating a surplus of money. People use that extra money to buy bonds and other financial assets, which bids up bond prices and pushes the nominal interest rate down toward equilibrium.

If the nominal interest rate is below equilibrium, the quantity of money demanded is greater than the quantity supplied, creating a shortage of money. People sell bonds and other financial assets to get money, which lowers bond prices and pushes the nominal interest rate up toward equilibrium.

This connects to a key relationship from earlier in the unit: bond prices and interest rates move in opposite directions.

Shifts in the Money Market

Money demand shifts from a change in the price level, a change in real GDP, or a change in transaction costs. Money supply shifts only from central bank monetary policy. Here are the four basic outcomes:

• An increase in money demand shifts money demand right and raises the equilibrium nominal interest rate.
• A decrease in money demand shifts money demand left and lowers the equilibrium nominal interest rate.
• An increase in money supply shifts money supply right and lowers the equilibrium nominal interest rate.
• A decrease in money supply shifts money supply left and raises the equilibrium nominal interest rate.

How to Use This on the AP Macroeconomics Exam

Free Response

Label your axes correctly: nominal interest rate on the vertical axis and quantity of money on the horizontal axis. Draw money demand as a downward-sloping curve and money supply as a vertical line.

When a question gives you a change, decide first whether it shifts money demand or money supply, then show the direction of the shift and the new equilibrium nominal interest rate. Always state what happens to the equilibrium nominal interest rate, since that is usually the point being tested.

If the question continues into policy effects, connect the new nominal interest rate to investment and consumption, and then to aggregate demand. Use clear cause and effect language, such as "lower nominal interest rate leads to more investment, which increases aggregate demand."

MCQ

Watch for whether the question describes a shift of a curve or a movement along a curve. A change in the nominal interest rate alone moves you along money demand. A change in the price level, real GDP, or monetary policy shifts a curve.

Common Trap

When a question asks which central bank action fits a scenario, name the specific action that matches, not a list of every tool. Read carefully and answer the exact question asked.

Common Misconceptions

• The money supply curve is not upward sloping. It is vertical because the central bank sets it, independent of the nominal interest rate.
• A change in the nominal interest rate does not shift money demand. It causes a movement along the money demand curve. Only the price level, real GDP, or transaction costs shift the curve.
• The money market uses the nominal interest rate, not the real interest rate. The real interest rate belongs to the loanable funds market.
• Higher interest rates mean lower bond prices, not higher ones. Bond prices and interest rates move in opposite directions.
• An increase in the money supply lowers the equilibrium nominal interest rate. Students often flip the direction, so check the shift carefully.

zontal axis. Draw money demand as a downward-sloping curve and money supply as a vertical line, then mark equilibrium where they intersect.

Why is money demand downward sloping?

Money demand slopes downward because the nominal interest rate is the opportunity cost of holding money. When nominal interest rates rise, people want to hold less money and more interest-bearing assets.

Why is the money supply curve vertical?

The money supply curve is vertical because the money supply is set by the central bank and is independent of the nominal interest rate in the basic money market model.

What shifts money demand in AP Macro?

Money demand shifts when the price level, real GDP, or transaction costs change. A higher price level or higher real GDP increases money demand and shifts the curve right.

What happens when the money supply increases?

An increase in the money supply shifts the vertical money supply curve right. In the money market model, that lowers the equilibrium nominal interest rate.

Related AP Macroeconomics Guides

• 4.1 Financial Assets
• 4.3 Definition, Measurement, and Functions of Money
• 4.4 Banking and the Expansion of the Money Supply
• 4.2 Nominal vs. Real Interest Rates
• 4.6 Monetary Policy
• 4.7 The Loanable Funds Market