A bank run happens when many depositors try to pull their money out of a bank at the same time, because they fear the bank cannot pay everyone back. Banks lend out and invest most of the money you deposit and keep only a fraction on hand, so a sudden rush of withdrawals can force a bank to sell assets at a loss and can push an otherwise functioning bank into failure within days. The collapse of Silicon Valley Bank in 2023 showed how fast this can now happen.

Why a bank is vulnerable in the first place

A bank takes in deposits that customers can demand back at any time and uses that money to make loans and buy securities that pay back over months or years. That mismatch, short-term money funding long-term assets, is called maturity transformation, and it is the normal business of banking, not a flaw. It works because on any ordinary day only a small share of depositors want their cash, so the bank needs to hold only a fraction of deposits as ready money.

The weakness appears when confidence breaks. If enough depositors demand their money at once, the bank has to raise cash fast, usually by selling its securities. If those securities have fallen in value, the bank books a loss, its finances look weaker, and that can frighten still more depositors. The run feeds on itself.

How the Silicon Valley Bank run unfolded

Silicon Valley Bank is the clearest recent example, and the Federal Reserve documented it in detail in its April 28, 2023 review of the bank's supervision. On March 8, 2023, SVB's parent announced a plan to restructure its balance sheet: it had sold $21 billion of securities, was booking a $1.8 billion after-tax loss, and was trying to raise $2.25 billion in new capital. The announcement signaled distress.

The next day the dam broke. According to the Fed's review, "on March 9, SVB lost over $40 billion in deposits, and SVBFG management expected to lose over $100 billion more on March 10." The $40 billion that left in a single day was "roughly 85 percent of the bank's deposit base." To see how extreme that was, the Fed offered a comparison: the 2008 failure of Wachovia involved about $10 billion of outflows over eight days, and Washington Mutual about $19 billion over sixteen days. SVB lost four times Wachovia's total in one day.

Two features made it so fast. First, SVB's depositors were heavily concentrated among technology startups and venture capital firms, many connected to one another, and most of their balances were far above the insurance limit, so they had every reason to move first. Second, the panic spread online. The Fed concluded that "the combination of social media, a highly networked and concentrated depositor base, and technology may have fundamentally changed the speed of bank runs."

SVB could not meet the demands. On the morning of March 10, 2023 the California Department of Financial Protection and Innovation closed the bank and named the Federal Deposit Insurance Corporation as receiver. The FDIC said insured depositors would "have full access to their insured deposits no later than Monday morning, March 13, 2023," and it created a new entity, the Deposit Insurance National Bank of Santa Clara, to hold them.

Why deposit insurance is the thing that usually stops a run

The reason most people never join a bank run is that they do not need to. The FDIC insures deposits "to at least $250,000" per depositor, per insured bank, per ownership category, so an insured depositor gets their money back whether or not the bank survives. That guarantee removes the incentive to rush the exits, which is exactly why it exists. You can read how the coverage works in our explainer on FDIC deposit insurance.

SVB's problem was that most of its deposits were above that limit. Uninsured depositors had real money at risk and a strong reason to run, which is why the outflow was so violent. In that case regulators took the unusual step of protecting uninsured depositors too, to stop the panic spreading to other banks, but that is a policy decision made case by case, not a standing promise.

The central bank as lender of last resort

Deposit insurance removes most savers' reason to run, but it does not help a solvent bank facing a sudden cash crunch. That is the job of the central bank as lender of last resort: it can lend a bank cash against its good assets so the bank can meet withdrawals without dumping securities at a loss. After SVB failed in March 2023, the Federal Reserve set up an emergency facility, the Bank Term Funding Program, that let banks borrow against bonds valued at their original price rather than their fallen market price, precisely to stop forced sales from turning a liquidity scare into a wave of failures. The tool is powerful, but it is meant for a cash squeeze, not for a bank that is genuinely insolvent.

What a bank run means for an ordinary saver

For a normal customer the practical lesson is narrow and reassuring. If your money is in an FDIC-insured bank and your balances are within the coverage limits, a bank run elsewhere does not put your insured deposits at risk, and panic-withdrawing is unnecessary. The savers who get hurt are typically businesses and wealthy depositors with balances well above the limit, which is why they watch bank health closely and spread cash across institutions.

Understanding how banks actually use your deposits helps put the risk in proportion; our guide to how banks make money covers the lending and interest model that makes a run possible in the first place. The modern twist the Fed identified is speed: with mobile apps and social media, a run that once took days can now take hours, which is why regulators are rethinking how much ready cash banks must hold against their least stable deposits.