Fractional-Reserve Banking

A fractional-reserve banking system is the standard arrangement used in modern economies, where commercial banks lend out most of the deposits they receive, keeping only a small fraction in reserve to meet daily withdrawal demands. This system allows banks to create credit and the money supply to expand far beyond the central bank’s monetary base, but it also creates fragility: if too many depositors demand their money at once, a bank can fail.

How it works

A depositor walks into Bank A and deposits $1,000 in cash. Bank A credits the depositor’s account with $1,000. The bank now holds $1,000 in its vault.

The bank is required (or chooses) to keep a portion—say 10%—in reserve. That is $100. The remaining $900 can be lent out to borrowers. Bank A lends $900 to a business that needs capital for equipment.

The business withdraws the $900 and pays a supplier, who deposits the cash in Bank B. Bank B now has $900. It keeps 10% ($90) in reserve and lends out $810 to another borrower.

At this point:

• The original depositor has $1,000 in deposits at Bank A.
• Bank B’s customer has $900 in deposits.
• Total deposits: $1,900, created from $1,000 in original cash.

The money supply has expanded, even though no new base money was created. The banks created it through lending.

Money creation

This is the profound insight of fractional-reserve banking: banks create money when they lend. When a bank extends a $900 loan, it credits the borrower’s account with $900. That $900 is now money—spendable and part of the money supply. The bank did not have that $900 in its vault; it was created by the act of lending.

This is not counterfeiting. The bank has a legal, contractual claim on the borrower (the loan) that balances the bank’s liability to the depositor (the deposit). The $900 is backed by the loan contract, not by physical cash. This works as long as borrowers repay their loans and depositors do not all demand cash simultaneously.

The risk: bank runs

The system’s weakness is apparent: the bank has promised to pay $1,000 in cash on demand to the original depositor, but only has $100 in reserve plus a bunch of loans that will take years to be repaid.

If the depositor and Bank B’s customer both demand their cash, the bank has only $100 (plus whatever it can liquidate quickly). It is insolvent. This is a bank run—a panic where many depositors demand cash simultaneously, causing the bank to fail even if it is fundamentally sound.

Bank runs are catastrophic because they create contagion. If Bank A fails, people fear Bank B and Bank C might be next, so they withdraw from those banks too, triggering runs across the system. A solvent banking system can collapse in days.

Safeguards

Modern economies maintain fractional-reserve banking through several safeguards:

Deposit insurance. The government (via institutions like the FDIC in the US) insures deposits up to a limit (typically $100,000–$250,000). Depositors know their money is safe even if the bank fails, so they do not panic.

Lender of last resort. The central bank stands ready to lend to banks that face temporary liquidity crunches, via facilities like the discount window. This prevents routine liquidity shortages from becoming insolvency.

Reserve requirements. Regulation mandates that banks hold minimum reserves, constraining how much they can lend relative to deposits.

Regulation and supervision. Banks are examined regularly to ensure they are not taking excessive risks and hold adequate capital.

These safeguards make fractional-reserve banking stable, but they do not eliminate the fundamental fragility. A truly severe crisis (like 2008) can overwhelm these protections.

See also