The required reserve ratio (rr) is the fraction of deposits that depository institutions must hold as reserves rather than lend out. In AP Macro, it determines the maximum money multiplier (1/rr), which tells you the largest possible expansion of the money supply from new excess reserves.
The required reserve ratio is the percentage of customer deposits a bank legally has to keep on hand as reserves instead of lending out. If the ratio is 10% and you deposit $1,000, the bank must hold $100 as required reserves. The other $900 is excess reserves, and excess reserves are what banks lend out to create new money (EK POL-2.A.3 and POL-2.A.4).
Here's why this one number matters so much. It's the reciprocal of the maximum money multiplier. With a 10% ratio, the multiplier is 1/0.10 = 10, so a $900 loan can ultimately support up to $9,000 in new money as deposits get re-lent through the banking system. The ratio is also one of the central bank's monetary policy tools (EK POL-1.D.2), though in an ample-reserves economy like the United States it takes a back seat to administered interest rates like interest on reserves.
This term sits at the center of Unit 4 (Financial Sector) and bridges two topics. In Topic 4.4, it powers the money creation math you need for LO 4.4.B and LO 4.4.C, where you calculate how a new deposit or an open market operation changes the money supply using balance sheets. In Topic 4.6, it appears under LO 4.6.A as one of the listed tools of monetary policy, alongside open market operations and administered rates. The CED is explicit that which tools matter depends on whether the banking system has limited or ample reserves, and that framing shows up directly in multiple choice questions. If you can't compute 1/rr quickly, a big chunk of Unit 4 falls apart.
Keep studying AP® Macroeconomics Unit 4
Money multiplier and excess reserves (Unit 4)
The required reserve ratio and the money multiplier are two views of the same thing. The ratio tells banks what to hold, and its reciprocal (1/rr) tells you the maximum the banking system can multiply new excess reserves into new money.
Bank balance sheets (Unit 4)
Calculation FRQs in Topic 4.4 often hand you a balance sheet and a reserve ratio. You split total reserves into required reserves (deposits times rr) and excess reserves, and only the excess can be loaned out to expand the money supply.
Ample reserves framework (Unit 4)
In an economy with ample reserves, banks already hold far more than required, so changing the ratio barely moves anything. That's why the Fed now steers the economy with administered interest rates like interest on reserves instead. The CED flags this distinction directly.
Open market operations and monetary policy (Unit 4)
Classic exam problems combine the two tools. The Fed buys bonds to inject reserves, then the required reserve ratio determines how far those reserves multiply. A $500 million purchase with a 10% ratio means up to $5 billion in new money.
This is a calculation workhorse. Expect multiple choice stems like "the Fed conducts an open market purchase of $500 million and the required reserve ratio is 10%; what is the maximum potential increase in the money supply?" The move is always the same. Find the multiplier (1/rr), find the change in excess reserves, multiply. Questions also test the gap between maximum and actual money expansion, so know the leakages. If banks hold extra excess reserves or people hold cash, the real change is smaller than 1/rr predicts. Finally, watch for ample-reserves framing. If a question says the banking system has ample reserves, changing the reserve ratio is not the effective tool; administered interest rates are. No released FRQ has hinged on the term verbatim, but balance sheet and money multiplier calculations are standard Unit 4 FRQ material under LO 4.4.C.
They're reciprocals, not the same number. The required reserve ratio is a fraction of deposits banks must hold (like 0.10), while the money multiplier is how many times new excess reserves can expand into money (1/0.10 = 10). A common exam trap is multiplying by the ratio when you should multiply by 1/rr, or forgetting that the multiplier applies to excess reserves, not the whole deposit.
The required reserve ratio is the percentage of deposits that banks must hold as reserves and cannot lend out.
The maximum money multiplier equals 1 divided by the required reserve ratio, so a 10% ratio means a multiplier of 10.
Only excess reserves get loaned out and multiplied, so the maximum change in the money supply equals the change in excess reserves times 1/rr.
The actual money expansion is usually smaller than the maximum because banks may hold extra excess reserves and people may hold cash instead of depositing it.
In an ample-reserves banking system like the United States, the required reserve ratio is not the Fed's go-to tool; administered interest rates such as interest on reserves do the work.
Raising the ratio shrinks the multiplier and is contractionary; lowering it grows the multiplier and is expansionary.
It's the fraction of deposits that depository institutions must hold as reserves rather than lend out. Its reciprocal (1/rr) gives the maximum money multiplier, which caps how much the banking system can expand the money supply.
Divide 1 by the ratio written as a decimal. A 10% ratio gives 1/0.10 = 10, a 20% ratio gives 1/0.20 = 5, and a 5% ratio gives 1/0.05 = 20.
No. The ratio is what banks must hold (a fraction like 0.10), while the multiplier is its reciprocal (10) and measures how far excess reserves can expand into new money. Mixing them up is one of the most common Unit 4 calculation errors.
Not really. The U.S. has an ample-reserves banking system, so the Fed relies on administered interest rates like interest on reserves instead. The AP CED expects you to know which tools work in ample versus limited reserves economies.
Because of leakages. If banks hold extra excess reserves instead of lending everything out, or if borrowers hold cash instead of redepositing it, the multiplication process stalls before reaching the maximum. AP multiple choice loves testing this gap.
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