In real life, depositors often withdraw cash from banks more or less, making some cash flow out of the banking system, resulting in so-called cash leakage.

Generally speaking, the party accepting bank loans from the excess deposit reserve ratio will not transfer all the loans or put them into production, and may also have some cash leakage, which is represented by δ C. The ratio of the cash leaked from the banking system (that is, the cash in circulation δ C) to the total bank deposits (δD) from the excess deposit reserve ratio is called the cash leakage rate, in which C indicates that the cash leaked from the banking system is out of the bank's control and can be used for banks.

Cash leakage is a phenomenon that customers withdraw deposits from banks and ask for cash, so that cash flows out of the commercial banking system as a reserve. When there is cash leakage, the deposit reserve of the banking system will be reduced, that is, the funds for banks to expand loans by absorbing deposits will be reduced accordingly, thus weakening the ability of banks to create derivative deposits. Cash leakage is mainly determined by the disposable income level of non-banking industry, the acquisition of expected opportunity cost, the degree of inflation and the service level of banking industry.