Stop-Loss Order

A stop order carries two prices in practice, even though only one is specified. The stop price is the trigger condition monitored by the exchange or broker; the execution price is whatever the book supplies once the order goes live. Until the trigger is touched, the order sits outside the visible limit order book and contributes no liquidity. On triggering, it becomes an ordinary market order and walks the opposite side of the book, consuming the best bid (for a sell stop) and then progressively worse prices until filled.

The gap between stop price and realised fill is called slippage. Its size depends on depth at the touch, tick size, and whether the trigger event was a gradual drift or a discontinuous jump. In a fast market, or across an overnight gap, the first available price may sit far below the stop, which is precisely why a stop caps intent rather than outcome.

A stop-limit order replaces the market order with a limit order at a stated limit price once triggered. This bounds the execution price but reintroduces execution risk: if the market gaps straight through the limit, the order rests unfilled and the position remains exposed. Candidates should recognise the trade-off explicitly, since price certainty and fill certainty cannot both be secured by a single instruction.

A trailing stop specifies the trigger as a distance, in currency or percentage terms, below the highest price reached since entry for a long position. As the price rises the stop ratchets upward and never retreats, converting the instruction into a mechanical profit-protection device. Buy stops above the market serve the mirror function for short sellers, whose theoretical loss is unbounded, and are also used by momentum traders to enter on a confirmed breakout rather than to exit.

Stops cluster at psychologically salient levels, round numbers, prior highs and lows, and widely quoted technical support. Because triggered stops become market orders, a cluster represents latent one-directional demand for liquidity that materialises only after the price has already moved. This is procyclical: selling begets selling. Regulators addressed the resulting fragility through mechanisms such as limit up-limit down price bands and single-stock circuit breakers, which pause trading rather than allowing orders to sweep an empty book.

Stops also interact with leverage. An investor holding a margined long faces a maintenance margin call at a computable price; a stop placed above that trigger price is an attempt to liquidate voluntarily before the broker liquidates involuntarily. In the FX and futures markets, where positions are marked continuously, this discipline is standard practice.

Be able to classify any described order along the standard dimensions: execution instruction, which governs how and at what price the order is filled; validity instruction, which governs when it may be filled, such as day, good-till-cancelled or immediate-or-cancel; and clearing instruction, which governs settlement, including whether a sale is long or short. A stop is an execution instruction, and it can be combined with a limit and any validity term.

Expect scenario questions that name a current price, a stop price and the next traded prices, then ask for the realised exit or whether the order fills at all. Work through the trigger first, then the fill, and never assume they coincide. You should also be able to explain why stops behave as short volatility positions and why they systematically underperform in markets that exhibit sharp reversals.