What it means
The mechanics are deliberately simple. You name a stop price below the current market level, the order sleeps until the share trades there, and it then becomes a market order that sells at whatever price the market offers next.
That last detail is where most of the confusion in business conversations comes from. Stop-losses matter because human beings are poor at cutting losing positions.
Deciding your exit while you are calm, then delegating the decision to a broker's system, removes the temptation to hold on hoping for a recovery that may never arrive. The usual way to set the level is as a percentage below your entry price or below a recent high, commonly somewhere between 5% and 20% depending on how much the share normally moves.
A share that swings 4% on a quiet day needs a wider stop than a steady utility, otherwise ordinary noise will trigger a sale you never wanted. A trailing stop is the most useful variant.
Instead of a fixed price, it sits a set distance below the highest price reached since you bought, so it ratchets upward as the position gains and locks in more of the profit without capping the upside. The main weakness is gapping, where a share reopens far below its previous close after news and the stop fills at the first available price.
In a disorderly market a stop set at $72 can easily fill in the $60s, which is exactly the scenario that pushes cautious investors towards a stop-limit instead.
In practice
Real-world examples.
Example
A retail investor with a full-time job sets 15% stop-losses across her portfolio so that a bad week cannot become a disaster while she is in meetings. One holding triggers during a profit warning and exits at a 16% loss instead of the 40% fall that followed.
Example
A commodity trading desk at a food manufacturer uses stop-losses on its speculative hedging book, with the risk manager reviewing every trigger the following morning. The rule exists mainly to stop a single trader quietly nursing a losing position.
Example
An estate executor holding a large single-share inheritance places a trailing stop 12% below the running high. The share rises for four months, the stop follows it upward, and when the trend reverses the estate exits well above the original valuation.
Think of it
“Stop-loss protects from further losses-automatic sell if price drops.
Formula
Calculation
Stop price = entry price x (1 - chosen tolerance), and realised loss = (entry price - fill price) x number of shares.
An investor buys 1,500 shares at $80 each, committing 1,500 x $80 = $120,000, and decides they will not risk more than roughly 10%. The stop price is $80 x (1 - 0.10) = $72.
Weak results push the share through $72 and the order fills at an average of $71.40 as sellers queue up. Proceeds are 1,500 x $71.40 = $107,100, so the loss is $120,000 - $107,100 = $12,900. That equals 10.75% of the original $120,000, slightly worse than the 10% target because the fill came in $0.60 below the trigger.Case study
Seen in the real world.
This is an illustrative and clearly fictional scenario. Ashfield Lane Investments, an invented advisory firm serving around forty private clients, reviewed a decade of its worst outcomes and found that most of the damage came from a handful of positions held far too long after they began falling. No client had ever lost badly on a position that was sold at a 15% decline.
The fictional partners introduced a house rule: every discretionary equity position gets a trailing stop 18% below its running high, wide enough to survive ordinary swings. In the first full year, nine positions triggered, of which four subsequently recovered and five continued falling by an average of a further 22%.
The firm's illustrative annual letter was honest about the cost of the four recoveries, estimated at $310,000 of forgone gains, against roughly $1.1m of losses avoided on the other five. Clients accepted the rule because it was stated in advance rather than argued about after the fact.
Watch out
Common mistakes.
- Treating the stop price as the price you will receive, when a stop-loss becomes a market order and can fill materially lower in a fast or gapping market.
- Setting stops so tight that normal daily volatility knocks you out of good positions repeatedly, racking up dealing costs and taxable events for nothing.
- Placing a stop and then never revisiting it, so a position that has doubled is still protected at a level set against the original purchase price.
Questions
People also ask.
Does a stop-loss work overnight or at weekends?
The order rests until the market opens, so news released while trading is closed can trigger it at the opening price rather than your chosen level.
Should long-term investors use stop-losses at all?
Many do not, on the view that they turn temporary declines into permanent losses, so the tool suits traders and concentrated positions more than diversified buy-and-hold portfolios.
What is the difference between a stop-loss and a trailing stop?
A stop-loss sits at a fixed price you set once, while a trailing stop moves up automatically as the price rises and locks in more of the gain.
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