In AP Macro, the supply of money is the total quantity of money available in the economy, determined by the central bank's monetary policy rather than the nominal interest rate, which is why the money supply curve is drawn as a vertical line in the money market graph (Topic 4.5).
The supply of money is the total amount of money available in the economy at a given time, including currency in circulation and demand deposits (checking account money). Here's the part the AP exam actually cares about. Per EK MKT-3.A.2, the money supply is set by the central bank through the monetary base, and it does NOT respond to the nominal interest rate. That's why you draw it as a vertical line on the money market graph. Banks don't suddenly create more money supply just because interest rates rise; only the central bank moves that line.
This makes the money supply fundamentally different from the supply curves you drew in micro or Unit 1. A normal supply curve slopes upward because higher prices coax out more output. The money supply is a policy choice. When the Fed conducts expansionary monetary policy, the vertical line shifts right and the equilibrium nominal interest rate falls. Contractionary policy shifts it left and the rate rises. Where this vertical supply line crosses the downward-sloping money demand curve, you get the equilibrium nominal interest rate (EK MKT-3.B.1).
The supply of money lives in Topic 4.5 (The Money Market) in Unit 4: The Financial Sector, supporting learning objectives 4.5.A (define money supply), 4.5.B (define money market equilibrium), 4.5.D (explain what shifts supply and demand), and 4.5.E (explain how those shifts change the equilibrium nominal interest rate). It's one half of the money market graph, which is one of the must-know graphs in AP Macro. Beyond Unit 4, the money supply is the lever the central bank pulls for all of monetary policy, so it connects directly to how the Fed fights recessions and inflation later in the course. If you can't draw and shift the money supply curve correctly, the whole monetary policy chain falls apart.
Keep studying AP Macroeconomics Unit 4
Demand for Money (Unit 4)
Money supply is the vertical half of the money market; money demand is the downward-sloping half. Demand slopes down because higher nominal interest rates raise the opportunity cost of holding cash. Supply stays vertical because the central bank, not the interest rate, decides how much money exists.
Monetary Policy (Unit 4)
Monetary policy IS the act of shifting the money supply curve. Expansionary policy (like the Fed buying bonds) shifts money supply right and lowers the nominal interest rate; contractionary policy shifts it left and raises the rate. Per EK MKT-3.D.1, monetary policy is the shifter to know for the supply side.
Money Market Graph (Unit 4)
On the AP money market graph, the money supply is the vertical line, money demand slopes down, and the nominal interest rate sits on the vertical axis. Drawing money supply as upward-sloping is one of the most common graph errors on FRQs.
Monetary base (Unit 4)
The monetary base (currency plus bank reserves) is what the central bank directly controls. The broader money supply grows out of that base through bank lending, so the base is the raw material and the money supply is the finished product.
Money supply questions almost always run through the money market graph. MCQs give you a Fed action (like increasing the money supply) and ask for the effect on the nominal interest rate. The answer chain is mechanical. Money supply shifts right, there's a temporary surplus of money at the old rate, and the nominal interest rate falls to restore equilibrium (EK MKT-3.C.1). Practice questions also test the reverse setup, like a central bank holding the rate at 3% when equilibrium is 5%, which creates a shortage of money. On FRQs, expect to draw a correctly labeled money market graph with a vertical money supply curve, show the shift from a policy action, and identify the new equilibrium nominal interest rate. Labels matter. The vertical axis is the nominal interest rate, not just "price," and the supply curve must be vertical.
The monetary base is the narrow foundation, currency in circulation plus bank reserves, that the central bank directly controls. The money supply is the broader total that includes demand deposits created when banks lend. The CED frames it this way (EK MKT-3.A.2). Given a monetary base set by the central bank, the resulting money supply is fixed with respect to the interest rate. So the base is the input, the money supply is the outcome you graph.
The money supply curve is vertical because the central bank sets the quantity of money, so it does not change when the nominal interest rate changes (EK MKT-3.A.2).
Equilibrium in the money market happens where money supply equals money demand, and that intersection determines the nominal interest rate (EK MKT-3.B.1).
An increase in the money supply shifts the vertical curve right and lowers the equilibrium nominal interest rate; a decrease shifts it left and raises the rate.
Monetary policy is the main shifter of money supply, while changes in the price level or income shift money demand instead (EK MKT-3.D.1).
If the interest rate sits above or below equilibrium, the resulting surplus or shortage of money pushes the nominal rate back toward equilibrium (EK MKT-3.C.1).
The money market determines the nominal interest rate, not the real interest rate, so label your graph's vertical axis accordingly.
It's the total quantity of money available in the economy, including currency and demand deposits, set by the central bank. On the AP money market graph (Topic 4.5), it's drawn as a vertical line because it doesn't depend on the nominal interest rate.
Because the central bank decides the quantity of money through its control of the monetary base, the amount supplied doesn't change when the nominal interest rate changes (EK MKT-3.A.2). A vertical line shows that fixed quantity at every interest rate.
No, it lowers them. When the Fed increases the money supply, the vertical curve shifts right, creating a temporary surplus of money at the old rate, and the nominal interest rate falls until the market clears (EK MKT-3.C.1).
Money demand slopes downward because higher nominal interest rates make holding cash more costly, so people hold less of it. Money supply is vertical because it's a central bank policy decision, not a market response to interest rates.
No. The monetary base is just currency in circulation plus bank reserves, which the central bank directly controls. The money supply is broader because it also includes demand deposits that banks create through lending.