Stop-Loss Order

A stop-loss order is an instruction to sell an asset (or buy it back, for a short position) once its price reaches a chosen trigger level, called the stop price, in order to cap a loss. Until the stop price is reached the order is dormant and invisible to the market; once it is triggered it becomes a live market order or, in the stop-limit variant, a limit order. Stop-losses are used by investors in shares, by currency traders and, very widely, by traders on crypto exchanges.

A stop-loss is a risk-management tool rather than a guarantee. It decides when to exit, not the price received. It is closely tied to margin trading and leverage, where a planned exit can prevent a position from reaching a margin call or forced liquidation.

Think of a stop-loss as a smoke alarm wired to the exit door. You buy something at 100 and decide in advance that if it ever falls to 90, you want out, whatever happens. You set the alarm at 90 and stop watching. Nothing happens while the price stays above 90; once it touches 90, the door swings open and you leave.

The catch is that you leave at the price on the other side of the door, not the price on the alarm. If the price drifts smoothly to 90, you sell near 90. If it jumps overnight from 95 to 80, the alarm goes off at 80 and that is roughly where you get out. A stop-loss limits how long you hold a losing position, not exactly how much you lose.

A sell stop is placed below the current price for a long position; a buy stop is placed above the current price to close a short position. When the market trades at or through the stop price, the order is triggered. Depending on the venue, the trigger may be the last traded price, the bid or offer, or, on many crypto derivatives platforms, a "mark price" derived from several spot exchanges to reduce the effect of a single bad trade.

The loss a stop is designed to accept can be estimated in advance:

• $P_{\text{entry}}$ is the price at which the position was opened.
• $P_{\text{stop}}$ is the stop price.
• $Q$ is the number of shares, coins or contract units held.

A trader who buys 50 shares at 40 and sets a stop at 36 plans to lose $(40 - 36) \times 50 = 200$, before fees. Many traders size positions backwards from this formula: if they will risk only 200 on a trade and the stop is 4 below entry, they buy no more than 50 shares. The actual loss can be larger if the fill comes below 36.

• Stop-market order. Becomes a market order when triggered. It almost always fills, but the price can be well beyond the stop in a fast market.
• Stop-limit order. Becomes a limit order at a set limit price. It caps the exit price but may not fill at all if the market gaps through the limit, leaving the position open.
• Trailing stop. The stop price follows the market at a fixed distance or percentage as the price moves in the trader's favour and stays put when it moves against them, locking in part of a gain.
• Take-profit order. The mirror image: a resting order to close at a target price above the market for a long position. Crypto and FX platforms often pair it with a stop-loss in a single "one-cancels-the-other" bracket.

Share markets close overnight, so a stock can open far below the previous close after bad news; a stop-market order then fills near the opening price, not the stop. During the US "flash crash" of 6 May 2010, prices collapsed and recovered within minutes, and stop-market orders triggered in that window were filled at whatever bids remained, in some cases far below the stop price.

In foreign exchange, trading runs continuously through the week, but gaps occur over weekends and around shocks such as the Swiss National Bank's removal of the franc's minimum exchange rate in January 2015, when many retail stop-losses on the franc were filled far beyond their stop levels.

On centralized crypto exchanges trading never closes, but thin weekend books and high volatility mean triggered stops can cascade: one stop sells into the book, pushes the price lower and triggers the next. Clusters of stops at obvious round numbers are sometimes called liquidity pools by traders, and large players are often accused of pushing prices toward them, a practice informally called a "stop hunt". On perpetual futures, a stop placed well inside the liquidation price lets a trader exit on their own terms before the exchange's liquidation engine takes over.

Stop-losses are blunt. A tight stop can be hit by normal day-to-day noise just before the price recovers, turning a sound trade into a realised loss. Stops left resting with a broker or exchange are only as reliable as that venue's systems during stress, when outages are most likely. On a decentralized exchange there is usually no native stop order; users depend on bots or third-party services that submit the trade when a price oracle or pool price crosses the trigger, adding execution risk and gas fees. Used with that in mind, a stop-loss remains one of the simplest forms of risk management available to an individual trader.

• Investor.gov (SEC): Stop Order
• Investor.gov (SEC): Types of Orders