Intermediatemacroeconomics
Fractional Reserve Banking Explained
Overview
Modern banking rests on a simple but powerful idea: banks do not keep all deposits in the vault. They hold a fraction as reserves and lend the rest, earning interest on the loans while depositors keep the convenience of on-demand balances. This lesson uses balance-sheet T-accounts to show exactly how a loan creates a deposit, why the system multiplies the monetary base, and what risks fractional reserves introduce. It is the mechanical heart of the money supply — and of bank fragility.
Learning objectives
- Explain what fractional reserve banking means in one precise sentence.
- Use a bank T-account to show how a loan creates a deposit.
- Distinguish required reserves from excess reserves.
- Describe how fractional reserves let banks create broad money.
- Identify the liquidity risk created by maturity mismatch.
The Core Idea: Lend Most, Keep Some
Under fractional reserve banking, a bank keeps only a fraction of its deposit liabilities as reserves — vault cash plus balances at the central bank — and puts the rest to work as loans and investments. The fraction held back is the reserve ratio, set partly by regulation and partly by the bank's own caution. Depositors, meanwhile, treat their full balances as money available on demand. The system works because on any normal day only a small share of depositors withdraw at once, so the bank can safely lend out the rest and earn the interest spread that is its profit.
A T-Account Walkthrough: How a Loan Creates Money
Picture a new bank receiving a 1,000 in reserves and liabilities of 100 but may lend 900 loan, it does not hand over vault cash; it credits the borrower's checking account. Now deposits total 1,000 of reserves. No new base money was printed, yet the money supply (deposits) grew — the loan created the deposit, not the other way around.
Textbook shorthand says 'banks take deposits and lend them out,' but the balance-sheet truth is sharper: bank lending creates deposits. The constraint on lending is profitable borrowers and capital rules, not a pre-existing pile of deposits.
Required vs Excess Reserves
Required reserves are the minimum a bank must hold against certain deposits, dictated by the reserve ratio. Any reserves above that minimum are excess reserves, which the bank can lend out or leave parked at the central bank earning interest. In normal times banks hold little excess because idle reserves earn less than loans; in crises they may hoard excess reserves, which weakens the link between the monetary base and broad money. Since 2020 the US Federal Reserve has set required reserve ratios to zero, making the distinction historical there — but the economics of reserve choice remain.
From One Bank to the Whole System
The 810, and so on down the chain. Each round creates new deposits from the reserves freed by the last, which is the money multiplier process covered in the next lesson. The key point here is that no single bank creates money out of thin air beyond its own balance sheet — the system-wide expansion emerges from the network of banks each doing ordinary fractional-reserve lending. This is why monetary policy works through the banking system rather than around it.
The Built-In Fragility: Maturity Mismatch
Fractional reserve banking bakes in maturity mismatch: banks borrow short (deposits withdrawable on demand) and lend long (multi-year mortgages and business loans). If too many depositors demand cash at once — a bank run — the bank cannot liquidate long-term loans fast enough and can fail even while solvent on paper. Deposit insurance, the central bank's lender-of-last-resort role, and liquidity regulations all exist to manage this structural fragility. Understanding the mismatch is essential: it explains both why banking is profitable and why it periodically needs rescuing.
A bank can be solvent (assets exceed liabilities) yet die from illiquidity (cannot meet today's withdrawals). Fractional reserves make liquidity, not just solvency, a survival condition.
Key points
- Banks hold a fraction of deposits as reserves and lend the rest; the reserve ratio governs the split.
- A bank loan creates a matching deposit — lending creates money, not the reverse.
- Required reserves are the regulatory minimum; excess reserves are the lendable surplus.
- System-wide deposit expansion emerges from many banks repeating the lend-and-redeposit cycle.
- Borrowing short and lending long (maturity mismatch) makes banks profitable but run-prone.
Common misconceptions
✓ Truth: Banks create new deposit balances when they lend; the original reserves mostly stay on the balance sheet. Total deposits in the system far exceed total reserves — that is the whole point of fractional reserves.
✓ Truth: Reserves protect against withdrawals, but a bank can still fail from bad loans destroying its capital. Solvency (assets minus liabilities) and liquidity (cash on hand) are two different survival conditions.
✓ Truth: Banks create deposits, but every deposit is matched by a loan asset on the balance sheet — nothing is created without an offsetting obligation. The system is leveraged, not magical.
Practice questions
Q1. A bank receives a $2,000 deposit when the reserve requirement is 10%. After keeping required reserves, what is the maximum new loan it can make from this deposit?
- $2,000
- $1,800
- $200
- $1,000
Required reserves are 10% of 200. The bank may lend the remaining $1,800, which it does by crediting the borrower's deposit account — creating new broad money in the process.
Q2. On a bank's T-account, a new $500 loan appears as:
- A $500 decrease in reserves and a $500 decrease in deposits
- A $500 loan asset and a $500 deposit liability
- A $500 increase in equity only
- No change until the borrower repays
Making the loan creates two entries: the loan as an asset (someone owes the bank) and the credited deposit as a liability (the bank owes the depositor). Both sides of the balance sheet expand by $500.
Q3. Maturity mismatch in banking refers to:
- Loans maturing faster than deposits
- Borrowing short-term (deposits) while lending long-term
- Assets and liabilities in different currencies
- Banks opening branches in mismatched locations
Banks fund themselves with demand deposits withdrawable at any time but invest in long-term loans like mortgages. This borrow-short/lend-long structure is profitable but creates run risk.
Q4. If banks collectively decide to hold large excess reserves during a crisis, the likely macro effect is:
- A stronger money multiplier and faster broad-money growth
- A weaker link between the monetary base and broad money
- An automatic fall in the reserve requirement
- Immediate hyperinflation
Excess reserves are base money that is not being relent through the deposit multiplier. When banks hoard them, base-money injections translate weakly into broad money and credit — exactly what happened after 2008.
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Frequently asked questions
What is a T-account and why do economists use it?
A T-account is a simplified balance sheet with assets on the left and liabilities plus equity on the right. Economists use it to trace exactly how a transaction — like a new loan — changes both sides while keeping the books balanced.
Can a single bank multiply deposits by itself?
Only modestly. A single bank loses most of each loan's proceeds when the borrower spends them at other banks. The full multiplier effect requires the whole banking system recycling deposits from bank to bank.
What limits how much a bank can lend?
Three main limits: finding creditworthy borrowers, capital adequacy rules that require equity against risky assets, and reserve/liquidity requirements. In modern systems, profitable lending opportunities usually bind before reserves do.
Why don't banks just hold 100% reserves to be safe?
That is 'narrow banking,' and it would eliminate bank runs — but also eliminate the interest income that lets banks pay for free checking and cheap loans. Society accepts some fragility in exchange for credit intermediation.