How often do stock market crashes happen? The historical frequency

How often do stock market crashes happen under a strict definition?

Under a strict definition, stock market crashes are rare. A standard reference states that they are not common, and it describes a crash as a fall of more than 10% over several days across a major cross-section of a market. Big falls cluster in a few episodes across a century, such as 1929 and 1987, while smaller declines appear much more often.

Looser definitions raise the count. A correction of 10% to 20% and a bear market of 20% or more over at least 2 months both belong to the same family of falls, and each has its own frequency. The right answer to the question therefore starts with a second question: which fall do you mean?

Which definition sets how often stock market crashes happen?

Three labels cover most usage. A crash is a fall of more than 10% over several days. A correction is a decline of 10% to 20%. A bear market is a decline of 20% or more over at least 2 months. The labels overlap at the edges, so a single episode can carry 2 of them, such as a crash inside a longer bear market.

Pick the label that matches your decision. A board that fears a sudden loss of liquidity cares about crashes over days. A retirement plan that spans decades cares about bear markets and their length. Writing the label next to every count keeps comparisons honest, and it prevents the common error of mixing a daily crash with a multi-year bear market.

What does the record show for stock market crashes since 1929?

Federal Reserve History dates the 1929 crash to Black Monday, 28 October 1929, when the Dow Jones fell nearly 13 percent, followed by nearly 12 percent the next day. The index peaked on 3 September 1929 and closed on 8 July 1932 at 41.22, 89 percent below that peak. Black Monday on 19 October 1987 then took the Dow down 22.6 percent in one session.

The S&P 500 declines listed on Wikipedia show later episodes: 34% from 19 February to 23 March 2020, 27.55% from 3 January to October 2022, and 23% from a February high to 7 April 2025. 3 episodes of 20% or more began within 6 years. Counting over 6 years gives a very different answer from counting over a century, so the window belongs next to every count.

Why do stock market crashes arrive in clusters?

Crashes follow the build-up of leverage, valuations, and shared positions, so they bunch when those conditions peak and fade when balance sheets are cleaned. Wikipedia reports MIT research suggesting that crash frequency follows an inverse cubic power law, which means that small falls are common and very large falls are rare in a regular pattern.

The same source cites a 2011 study from the New England Complex Systems Institute that found a sharp rise in investor imitation in the year before each crash it examined. Both findings point to structure behind the timing: frequency reflects how crowded and how indebted the market is, and an average over a century hides that variation.

How long do stock market crashes and bear markets last?

A crash lasts days, and the bear market around it lasts months or years. Wikipedia reports that from 1926 to 2014 the average bear market lasted 13 months with an average cumulative loss of 30%, without naming the market. Its list records the S&P 500 falling 36.1% over 20 months from November 1968 and 27.1% over 21 months from November 1980.

Episodes differ widely around those averages. The 2020 fall ran from 19 February to 23 March, about 5 weeks, while the Dow’s decline from 3 September 1929 to 8 July 1932 lasted almost 3 years. Duration matters as much as size, because a long fall tests funding and patience, and a short one tests nerves.

How do you count stock market crashes for your own base rate?

Follow 5 steps: choose the index, write the definition, such as a fall of 20% or more from peak to trough, choose the window, such as 100 years, list the episodes from a public source and count each peak-to-trough fall once, then divide the number of episodes by the number of years. The result is a base rate per year that you can state with its definition and window.

As an illustration, 4 episodes in 40 years give 10% per year, and 1 episode in 40 years gives 2.5%. Both numbers are arithmetic examples that show how a count becomes a rate, and neither describes any real index. Use your own list, then adjust the rate with current readings, as the page on stock market crash probability explains.

How should the frequency of stock market crashes shape a plan?

Use the frequency as an anchor for risk sizing. A base rate says that falls of a given size occur at a known pace over long periods, and it leaves the next month open. As of October 2026 the sensible plan sizes risk to a fall that your finances can carry, whichever year it arrives.

The EQOS Asia method page explains how a structural score adds current conditions to the base rate, and a 30-minute pre-diagnostic applies it to your own exposure. The wider guide shows how the pieces fit. This page is general information, not investment advice.

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About the author

Stéphane Jambu

President, EQOS Forecast Asia

Stéphane Jambu leads EQOS Forecast Asia and works as a consultant in e-commerce, search visibility, and AI. LinkedIn profile