AP Syllabus focus: ‘The simple money multiplier can overstate expansion when banks hold excess reserves or the public holds more currency.’
The simple money multiplier is a useful benchmark for how deposits might expand from new reserves. In practice, real-world banking and household behavior create “leakages” that make actual money creation smaller.
What the simple money multiplier assumes
The simple money multiplier predicts the maximum potential expansion of checkable deposits from an increase in bank reserves, given a fixed required reserve ratio. It tends to be presented as a best-case, mechanical process.
Simple money multiplier: the maximum predicted ratio of the change in deposits (and thus money supply, in the simple model) to a change in reserves, assuming banks lend all excess reserves and the public holds no extra currency.
This model is “simple” because it relies on strong assumptions about banks and the public.
= simple money multiplier (unitless)
= required reserve ratio (decimal, e.g., 0.10)
Even when the central bank provides reserves, the link from reserves to deposits depends on choices made by banks and households.
Two key leakages that shrink deposit expansion
1) Banks hold excess reserves
Excess reserves are reserves held beyond what is required. When banks keep excess reserves instead of making loans, they reduce the amount of new lending and therefore reduce new deposit creation.
Why banks may hold excess reserves (reducing the multiplier effect):
Risk management: concern about borrower default or future withdrawals
Weak loan demand: few creditworthy borrowers or pessimistic outlook
Liquidity preference: desire to meet payments and withdrawals safely
Regulatory and internal constraints: policies that favour higher liquidity buffers
In the simple multiplier story, every dollar of excess reserves would have become a loan, creating deposits elsewhere. If that step is skipped, the deposit-creation chain is shorter and smaller.
2) The public holds more currency (currency drain)
A currency drain occurs when people choose to hold a larger share of money as cash instead of leaving funds in bank deposits. If households withdraw cash or prefer cash transactions, fewer funds remain in the banking system to support additional lending.
How higher currency holding lowers money creation:
Withdrawn cash reduces bank deposit liabilities
Lower deposits reduce the base on which banks can lend
Less redepositing means fewer rounds of deposit expansion
In short, even if loans are made, the process breaks down when recipients hold cash rather than redepositing funds.
Why “overstate” matters for interpreting policy and data
The simple money multiplier is best interpreted as a ceiling, not a guarantee. It can overstate expansion because actual outcomes depend on:
Banks’ willingness to convert reserves into loans (excess reserve leakage)
The public’s willingness to hold deposits rather than currency (currency leakage)
These leakages help explain why measured money growth may be modest even when reserves rise, and why money creation can vary across time as banking conditions and payment habits change.
FAQ
Yes. More complete models incorporate a currency-to-deposit ratio and an excess-reserve ratio, which mathematically reduce the predicted multiplier below $1/rr$.
Short-run shifts can come from changes in trust, payment frictions, or shock-driven precautionary behaviour. Seasonal spending patterns can also temporarily raise cash holdings.
Yes. Constraints can include insufficient capital, tighter underwriting standards, or a lack of creditworthy borrowers. These factors can raise excess reserves even without a change in required reserves.
You would look for currency rising relative to deposits and weaker growth in deposits than would be expected from reserve increases, alongside higher cash usage indicators.
It becomes less informative because $rr$ no longer meaningfully constrains lending; actual expansion depends more on banks’ and households’ behaviour, making leakages dominate the outcome.
Practice Questions
(2 marks) Explain how banks holding excess reserves can cause the simple money multiplier to overstate the expansion of the money supply.
Identifies that excess reserves are reserves not lent out / held beyond required (1)
Explains that less lending means fewer new deposits are created, so actual expansion is smaller than predicted by the simple multiplier (1)
(5 marks) Using the idea of “leakages,” explain two reasons why the simple money multiplier may overstate the expansion of deposits following an increase in reserves.
Defines or describes the simple multiplier as a maximum based on lending out excess reserves and redepositing (1)
Leakage 1: banks hold excess reserves (1)
Explains how this reduces loans and therefore reduces deposit creation rounds (1)
Leakage 2: public holds more currency / currency drain (1)
Explains how currency held outside banks reduces redeposits and the deposit base for further lending (1)
