Banks can create money through lending, but their ability to do so depends on reserves. Understanding required reserves, excess reserves, and how lending changes deposits is essential for explaining money supply expansion in a fractional-reserve system.

Core ideas: reserves and lending capacity

What banks mean by “reserves”

Bank reserves are assets held to meet deposit withdrawals and to satisfy legal or regulatory requirements. In AP Macroeconomics, reserves are typically treated as:

• Vault cash (currency in the bank)

• Deposits held at the central bank (e.g., balances at the Fed)

A higher required-reserve rule forces banks to keep more funds idle as reserves, limiting how much they can lend out of deposits.

Required reserves, excess reserves, and why the distinction matters

Banks commonly hold reserves for two reasons:

• Required reserves to meet the rule

• Excess reserves as a buffer or because lending opportunities are limited

Excess reserves are central to the syllabus point: bank reserves include required and excess reserves, and excess reserves support the expansion of the money supply—because they are the portion available (in principle) to back new loans and deposits.

Measuring reserves in a simplified AP framework

Banks compare their actual reserves to the required amount. The required amount depends on deposits and the required reserve ratio.

Graph illustrating how the maximum potential money/deposit creation from a fixed increase in reserves varies with the required reserve ratio. Visually, higher $rr$ implies a smaller multiplier effect (less potential expansion), while lower $rr$ implies greater potential expansion—connecting the rule to the system’s lending capacity. Source

In this framework, lending is constrained by whether a bank has excess reserves (or can obtain reserves) after meeting the required minimum.

How lending changes deposits and the money supply

The mechanical link: loans create deposits

When a bank makes a loan, it typically credits the borrower’s checking account. That action:

• Increases bank deposits (a liability of the bank)

• Increases the money supply (because checkable deposits are money in common measures)

• Uses available lending capacity that must remain consistent with reserve requirements

Why excess reserves “support” money creation

Excess reserves matter because they represent room to expand lending without violating the requirement:

• If a bank has no excess reserves, additional lending would push it below the required minimum unless it gains reserves (e.g., by attracting deposits or borrowing reserves).

• If a bank has excess reserves, it can make new loans and still meet the requirement, enabling additional deposit creation.

Key exam-safe statements

• Required reserves are the minimum; they are not lent out if the bank is exactly meeting the requirement.

• Excess reserves are the immediate source of potential new lending in the simplified model.

• New lending tends to raise deposits, and higher deposits tend to raise required reserves, tightening the constraint as expansion proceeds.

What can limit lending even with excess reserves?

Even if a bank has excess reserves, lending may not rise because:

• Borrowers may be less creditworthy, increasing perceived default risk

• Banks may choose to hold more excess reserves for precautionary reasons

• Banks may face internal capital/risk management rules that make them reluctant to expand loans

These considerations help explain why excess reserves can exist alongside weak loan growth, even though excess reserves still represent the system’s capacity to support expansion.