Monetary policy is easiest to understand by linking three diagrams that translate central bank actions into changes in interest rates, aggregate demand, and short-run output and inflation.

The three-model sequence (what you are modelling)

In the short run, AP Macroeconomics commonly models monetary policy as a chain:

• Reserve market: the central bank changes the supply of bank reserves, affecting an overnight policy rate

• Money market: the policy rate influences the nominal interest rate, changing the opportunity cost of holding money

• AD–AS: the interest rate changes planned spending, shifting aggregate demand (AD) and changing real output and the price level in the short run

Key idea: one policy move, three graphs

A single policy action should produce a consistent story across all three:

• Expansionary policy → interest rates fall → AD increases

• Contractionary policy → interest rates rise → AD decreases

Step 1: Reserve market (from policy action to the policy rate)

The reserve market focuses on banks’ demand for reserves and the central bank’s supply of reserves.

Reserve market equilibrium is shown by the intersection of banks’ demand for reserve balances and the Fed’s supply of reserves. The figure also highlights key administered rates (e.g., IORB and ON RRP) that help anchor overnight market rates, illustrating how changes in reserve conditions translate into movements in the policy rate. Source

• Supply of reserves is set by the central bank (treated as a shift factor)

• Demand for reserves is downward-sloping in the interest rate because higher rates make it more costly to hold reserves

When the central bank conducts expansionary monetary policy, it increases reserves:

• Reserve supply shifts right

• Equilibrium overnight interbank rate (often proxied by the federal funds rate) falls

With contractionary monetary policy, it decreases reserves:

• Reserve supply shifts left

• Equilibrium overnight rate rises

In the AP short-run linkage, the key output from the reserve market is the direction of movement in the policy rate.

Step 2: Money market (from the policy rate to the nominal interest rate)

The money market translates interest-rate changes into an equilibrium where money demand (MD) equals money supply (MS).

The diagram shows money market equilibrium where vertical money supply intersects downward-sloping money demand, determining the nominal interest rate. It visually supports the idea that, with $M^s$ fixed in the short run, changes in interest rates correspond to movements along the money demand curve toward the vertical supply line. Source

• Money demand slopes downward in the nominal interest rate because a higher interest rate raises the opportunity cost of holding money

• Money supply is drawn vertical when the central bank fixes the quantity of money (or monetary base with a stable multiplier)

A fall in the policy rate is modelled as a fall in the economy’s market nominal interest rate:

• Movement down along money demand to the given money supply

• The equilibrium nominal interest rate decreases

A rise in the policy rate is modelled as:

• Movement up along money demand

• The equilibrium nominal interest rate increases

In short-run policy modelling, it is common to treat real output (Y) and the price level (P) as unchanged at the instant the money market clears, so the interest rate adjusts first.

Step 3: AD–AS (from interest rates to output and the price level)

In the AD–AS model, the interest rate affects components of spending, especially:

• Investment (I): typically decreases when interest rates rise and increases when interest rates fall

• Interest-sensitive consumption: can also move with rates (e.g., durable goods)

Model the spending response as a shift in aggregate demand:

The figure illustrates how a shift in aggregate demand changes the short-run equilibrium in the AD–AS model. A rightward AD shift raises real output and the price level in the short run, while a leftward AD shift lowers both, matching the directional results used to score full credit on AP-style monetary policy questions. Source

• Expansionary policy (rates ↓) → AD shifts right → real GDP rises and the price level rises in the short run

• Contractionary policy (rates ↑) → AD shifts left → real GDP falls and the price level falls in the short run

Short-run results depend on the position/slope of SRAS, but the required AP linkage is directional consistency: policy → rates → AD → (Y, P).

Common modelling conventions (to earn full credit)

• Keep the sequence consistent: reserve market first, then money market, then AD–AS

• Use correct labels: nominal interest rate on the vertical axis in money market; price level and real output in AD–AS

• Emphasise that policy affects interest rates before output and prices adjust

• Do not shift SRAS for a pure monetary policy shock; the standard short-run channel is an AD shift