Cash in a vault is an expensive reserve
A bank cannot lend out every dollar deposited by customers: people need to withdraw cash, and payments must clear when money moves between banks. But keeping all those funds as paper bills would tie up space and security resources while earning nothing. Banks therefore hold only the physical cash needed to meet ordinary withdrawals and unexpected spikes in demand.
Most bank money moves as account entries
When a customer pays by card or transfers money, the bank usually does not move a matching bundle of bills. It updates account records and settles with other banks through the financial system. Those records are backed by a mix of assets, including loans and securities, as well as reserves used to make payments. The money is real, but its everyday form is an entry in a ledger rather than cash in a vault.
This arrangement lets banks support far more transactions than could be handled by passing physical currency around. It also creates a tradeoff: a bank must keep enough immediately available funds to handle withdrawals and payments, while putting other resources to work through lending and investment.
The vault is for access, not accumulation
Cash remains essential for customers who want bills and for situations in which electronic systems are unavailable. Yet vaults are designed around that practical need, not to mirror the total value of customer accounts. A bank’s visible stacks of currency are only the small, physical edge of a much larger system of records, loans, securities, and electronic settlement.
