Fractional-reserve banking
Money multiplier

The money multiplier is a heuristic traditionally used to demonstrate the maximum amount of broad money that could be created by commercial banks for a given fixed amount of base money and reserve ratio. This theoretical maximum is never reached, because some eligible reserves are held as cash outside of banks. Rather than holding the quantity of base money fixed, contemporary central banks typically focus on setting and maintaining target interest rates in order to satisfy their monetary policy goals, implying that the theoretical ceiling imposed by the money multiplier does not impose a limit on money creation in practice.
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