What is a flash crash
A flash crash is a very fast, deep fall in the price of an asset that is followed by a quick recovery of much of the loss, often within minutes.
Precise definition. Analysts use the term for an intraday move that is extreme compared with the asset's normal range (see average daily range). In this move, liquidity on the buy side disappears, and much of the drop reverses soon after. The recovery is what separates it from an ordinary crash or a market correction. The price is pushed by the mechanics of the order book rather than by a lasting change in value.
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A worked example (hypothetical)
Suppose a currency pair is trading quietly in a thin session, with few buy orders resting below the market.
- A large sell order arrives. It may be a genuine order, an algorithm reacting to a headline, or a fat finger error.
- The order eats through the few bids that exist. Each fill happens at a lower price than the one before.
- The falling price triggers clients' stop-loss orders. These become market sell orders and push the price lower still.
- Liquidity providers pull their quotes, so spreads widen sharply.
- Within minutes, buyers see the price as far below fair value and step in. The price climbs back towards where it started.
Now consider a trader who held a leveraged long position with a stop-loss placed just below the recent range. The stop was filled far below its level, because there were no buyers at the stop price. The trader also missed the rebound. If the account had little free margin, the broker's stop-out could close the position at the bottom. This is why leveraged CFD and forex trading can lose money very fast, even when the price later recovers.
Flash crash causes
- Thin liquidity, for example during holidays, session handovers or the market open (see opening and closing auctions).
- Algorithmic and high-frequency trading feeding on each other's orders (see API trading).
- Clusters of stop-loss orders that turn a fall into a cascade.
- Order errors and badly set order sizes.
- Sudden news that is quickly corrected or reassessed.
- Spillover from a related market (see financial contagion).
Where you see the term
- News and reports: after unusual intraday moves in currencies, indices, metals or crypto. Exchanges and regulators often publish post-event reviews.
- Platforms: in MetaTrader a flash crash shows up as a single long candle wick, with odd fills or slippage in the trade history. The account statement may show stops filled far from their set level (see account statement).
- Exchange rules: many exchanges use a circuit breaker to pause trading when prices move too far, too fast.
Edge cases
- No recovery: if the price does not come back, analysts call it a crash or capitulation, not a flash crash.
- Broker-only spike: a wick that appears in a single broker's feed but not in the wider market is a pricing error, not a market-wide flash crash.
- Black swan: a flash crash is a market-structure event. A black swan is a rare, high-impact event, usually with lasting effects.
Related terms
Fat tails and tail risk · Fill and partial fill · Fill or kill and IOC · Dead cat bounce · Catching a falling knife · Flight to quality · Risk management · Trading glossary
Frequent questions
What does flash crash mean in simple words?
It means the price falls very sharply in a very short time and then recovers much of the fall soon after.
Does a stop-loss protect against a flash crash?
Not fully. A standard stop-loss becomes a market order when it is triggered. In a flash crash, it can be filled far below the level you set.
Does the price always recover after a flash crash?
A quick recovery is part of the usual definition. Still, no one can know in advance whether a sharp fall will recover. Some falls keep going.
Are flash crashes more likely at certain times?
They are linked to thin liquidity. That makes quiet sessions, holidays and the moments around major news more exposed than busy trading hours.