Fractional Reserve Banking

How banks multiply money through lending and why it creates both opportunity and risk

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Money Supply (M0, M1, M2)

The Banking Multiplier Effect

When you deposit $1,000 in a bank, you might assume the bank stores that exact cash in a vault. In reality, banks keep only a small fraction as reserves and lend out the rest. This system—fractional reserve banking—is how modern banking multiplies money throughout the economy.

With a 10% reserve requirement, your $1,000 deposit can generate $10,000 in total money supply. Banks earn profits on loans, depositors keep access to funds, and the economy gets credit to grow. But this magic has a dark side: the system is inherently fragile.

The Core Mechanism

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1. Deposit

You deposit $1,000 cash in Bank A

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2. Reserve

Bank keeps $100 (10% reserves), lends $900

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3. Repeat

$900 gets deposited elsewhere, cycle continues

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Key Insight

Banks don't lend out depositors' money—they create new money when they make loans. Your deposit becomes the "reserve" backing multiple loans. This is why the money supply is much larger than physical currency.

Interactive: System Comparison

Compare fractional reserve banking to alternative systems and see how money creation differs.

Fractional Reserve (Current System)

Banks multiply deposits 10x or more

Credit available for business growth

Economy expands with money supply

Vulnerable to bank runs

Requires deposit insurance

Can amplify boom-bust cycles

Historical Context

Medieval Goldsmiths (1600s): Stored gold for merchants, issued receipts. Soon realized they could lend out gold since not everyone withdrew simultaneously—fractional reserve banking was born.
Bank of England (1694): First central bank established reserve requirements to stabilize the system after numerous banking panics.
Modern Era: Federal Reserve Act (1913) created formal reserve requirements in the US. During COVID-19 (2020), the Fed reduced reserve requirements to 0%—essentially removing the constraint entirely.