A stock market crash is a rapid and severe decline in stock prices across a broad market, such as the S&P 500 or Dow Jones Industrial Average. The October 19, 1987 crash shows how quickly one can happen: the Dow fell 22.6% in a single day.
Crashes often involve widespread selling, falling investor confidence, reduced liquidity and, in some cases, forced selling after margin calls. No official percentage defines a crash. The term refers to the speed, scale and severity of the decline.
A crash can happen in one trading session, as it did in 1987, or unfold over several sessions, as it did in 1929.
Stock Market Crash at a Glance
| Term | Typical meaning | Main distinguishing feature |
|---|---|---|
| Pullback | A modest decline in prices | Usually temporary and limited in scale |
| Market correction | A decline of about 10% from a recent high | A normal reversal after rising prices |
| Bear market | A broad market decline of about 20% or more | A deeper, sustained fall in market prices |
| Stock market crash | A sudden, severe and widespread collapse | Speed, panic and disorderly selling |
| Circuit breaker | A temporary trading halt | A market safety mechanism, not a type of crash |
A bear market generally means that a broad index has fallen at least 20% from a recent high and remains under pressure for a sustained period. A correction commonly refers to a decline of at least 10%.
How Does a Stock Market Crash Happen?
A crash often develops through several connected steps:
A shock changes investor expectations. The trigger may be economic weakness, higher interest rates, banking problems, geopolitical events, disappointing corporate earnings or the collapse of an asset bubble.
Investors begin selling. Selling can start with institutions, individual investors, traders or automated trading strategies.
Sell orders overwhelm available buyers. When fewer buyers are willing to trade, sellers may accept lower prices. Liquidity can shrink while volatility rises.
Leverage adds more selling pressure. Investors who borrowed money to buy stocks may receive margin calls after prices fall. If they cannot provide more cash or securities, their broker may sell investments to recover the loan.
Fear feeds the decline. Falling prices cause more investors to sell, which can push prices down further. This cycle is often called panic selling.
In 1987, portfolio insurance and derivatives helped accelerate selling after prices started to fall.
What Causes a Stock Market Crash?
Crashes usually result from several factors acting together rather than one isolated event.
Overvaluation and Speculation
A market becomes more vulnerable when stock prices rise much faster than company earnings, economic output or other fundamental measures. If investors start to believe prices have moved too far, a relatively small decline can trigger much larger selling.
Economic or Financial Shocks
Recessions, bank failures, credit-market stress, corporate bankruptcies and other unexpected changes can cause investors to reassess what stocks are worth.
Interest-Rate and Policy Changes
Higher interest rates can reduce the present value of future corporate profits. They can also make bonds or cash more attractive compared with stocks. Sudden policy changes may weaken investor confidence as well.
Leverage and Margin Calls
Borrowed money increases both gains and losses. During a crash, falling prices can force leveraged investors to sell, adding to the decline.
Loss of Confidence
Stock prices reflect expectations about future profits. When investors lose confidence in the economy, financial system or corporate earnings, they may sell before the full economic damage becomes visible.
What Is the Difference Between a Crash, Correction and Bear Market?
The main difference is how quickly and how far prices fall.
- A correction is usually a decline of around 10% from a recent high.
- A bear market is generally a decline of 20% or more in a broad market index.
- A crash is a sudden and unusually severe sell-off. It may develop into a bear market, but the terms do not mean the same thing.
A 20% decline spread over many months would usually be described as a bear market. A 20% decline in one day would more naturally be called a crash.
What Are Stock Market Circuit Breakers?
Stock market circuit breakers are temporary trading halts designed to slow disorderly selling. They give investors time to process new information before trading resumes.
In the United States, market-wide circuit breakers are based on the S&P 500's decline from the previous trading day's close:
- 7% decline: Level 1 trading halt
- 13% decline: Level 2 trading halt
- 20% decline: Level 3 halt for the rest of the trading day
Level 1 and Level 2 halts generally pause trading for 15 minutes when triggered before 3:25 p.m. Eastern Time.
Circuit breakers do not prevent losses or guarantee a recovery. They interrupt extreme trading conditions. They do not remove investment risk.
What Are the Effects of a Stock Market Crash?
A crash can affect:
- Individual stock portfolios
- Retirement accounts and pension funds
- Mutual funds and exchange-traded funds
- Corporate access to financing
- Consumer and business confidence
- Employment and economic growth
- Banks and other financial institutions
A crash does not automatically cause a recession. The 1987 crash was not followed by a banking crisis or recession. The 1929 crash occurred alongside wider banking and economic problems that contributed to the Great Depression.
What Are Some Major Stock Market Crashes?
The 1929 Stock Market Crash
On October 28, 1929, the Dow Jones Industrial Average fell nearly 13%. On October 29, it fell nearly 12%. By mid-November, the Dow had lost almost half its value from its peak.
The decline was followed by bank failures and a prolonged economic contraction. Historians distinguish the initial crash from the wider causes of the Great Depression.
The 1987 Stock Market Crash
On October 19, 1987, known as Black Monday, the Dow Jones Industrial Average fell 22.6% in one day. Automated and derivative-based selling intensified the decline, while weaknesses in the market's structure made the fall worse.
The Dow recovered much of the loss within two trading sessions and later moved above its pre-crash high.
What Should Investors Do During a Stock Market Crash?
The right response depends on an investor's time horizon, financial needs, risk tolerance and portfolio allocation. A practical checklist is:
- Avoid decisions based only on panic or headlines.
- Check whether the portfolio is properly diversified. Diversification can reduce the effect of one company, sector or asset class performing badly, although it cannot eliminate market losses.
- Review near-term cash needs. Money needed soon should not depend entirely on stock prices recovering quickly.
- Be cautious with margin and leverage. Borrowing can force sales at unfavorable prices.
- Revisit the investment plan instead of trying to predict the exact bottom.
- Remember that every stock may not recover. Broad markets can regain their losses while individual companies fail or remain permanently impaired.
A stock market crash is a sharp decline across the market, not proof that every company has become worthless. It is not automatically a buying opportunity either. The strongest protection is a portfolio and time horizon that can withstand substantial short-term losses without forcing an unnecessary sale.