Fractional-reserve banking

Fractional-reserve banking is the system of banking under which banks that take deposits from the public keep only part of their deposit liabilities in liquid assets as a reserve, and lend a percentage to borrowers, thus increasing the money supply by the loaned amount. Bank reserves are held as cash in the bank or as balances in the bank's account at the central bank. Fractional-reserve banking differs from the hypothetical alternative model, full-reserve banking, in which banks would keep all depositor funds on hand as reserves.

The country's central bank may determine a minimum amount that banks must hold in reserves, called the "reserve requirement" or "reserve ratio". Most commercial banks hold more than this minimum amount as excess reserves. Some countries, e.g. the core Anglosphere countries of the United States, the United Kingdom, Canada, Australia, and New Zealand, and the three Scandinavian countries, do not impose explicit reserve requirements at all.

Bank deposits are usually of a relatively short-term duration, and may be "at call" (available on demand), while loans made by banks tend to be longer-term, resulting in a risk that customers may at any time collectively wish to withdraw cash out of their accounts in excess of the bank reserves. The reserves only provide liquidity to cover withdrawals within the normal pattern. Banks and the central bank expect that in normal circumstances only a proportion of deposits will be withdrawn at the same time, and that reserves will be sufficient to meet the demand for cash.