How does a bank function?
The basic function of a bank is to take deposits (which become the bank’s liabilities) from depositors and invest them in a variety of assets (which become the bank’s assets) with the aim of making a profit between the income generated on the assets versus the income distributed on the deposits.
The assets invested in by the bank range from relatively safe and liquid instruments like cash and government bonds, but banks can also generate higher returns by investing in riskier instruments such as mortgage-backed securities (MBS) and loans (car loans, home loans, business loans, etc.). This setup is best demonstrated below (these figures are for demonstration purposes only, for a fictional bank with R1m in assets):
Source: Sanlam Investments Multi-Manager, March 2023
Banks don’t hold enough cash to pay out all deposits at once. This is because some of the bank’s assets are longer term in nature (think of a 20-year home loan, for example). The bank always tries to match the liquidity of the assets they invest in, to the expected withdrawals from depositors. Regulations also require banks to hold a certain percentage of their assets in safe and liquid instruments to be able to pay out the normal expected withdrawals from deposits.
A ‘run on the bank’ happens when the bank doesn’t have enough liquid assets to fund the withdrawals. However, deposits are spread between millions of depositors and the chance of them all wanting to withdraw all their cash at the same time is quite low. Through the years, the US government has also created additional support for the banking sector by insuring deposits up to USD250,000 in the case of a bank failure to further reduce the probability of a run on the bank.