Glossary pillar — part of an ongoing series defining trading terms in plain English. See also: What is VWAP?
A stop-loss is a standing order that closes your position automatically if price moves against you by a chosen amount. Its job is single and profound: deciding your maximum loss in advance, while calm, so you don't have to decide anything during panic. It is the single most important risk tool in trading, and the refusal to use one is the most common way beginners convert small mistakes into account-ending ones.
How it works mechanically#
You buy at 48. Nothing happens while price stays above 48, the stop triggers — becoming a market order that sells immediately at the best available price.
Two consequences of that mechanics:
- The trigger price is guaranteed; the fill price isn't. In fast markets or gaps, your sale may execute slightly below $48 (slippage). Stops limit damage; they don't guarantee exact prices.
- Stops don't work when markets are closed. A stock gapping overnight from 44 blows through any resting 44). This is why position sizing (Part 3 of our series) must assume worse-than-planned fills.
Stop types#
| Type | Behavior | Trade-off |
|---|---|---|
| Fixed stop | Static level until moved or hit | Simple; predictable risk |
| Trailing stop | Follows price by a set distance/percent, never retreats | Locks gains on runners; can be shaken out by noise |
| Guaranteed stop | Broker contractually fills at your exact price | Costs a premium; protects against gaps/slippage |
| Stop-limit | Triggers a limit order instead of market | Controls fill price but may not fill at all in fast moves — risky for exits |
Beginners should use plain fixed stops placed by chart structure. Trailing stops suit trend-following exits; guaranteed stops matter around events with gap risk.
Where to place them: structure decides#
A stop belongs where your trade idea is proven wrong — not where losses start feeling uncomfortable:
- Long off support at 49.40), because "support held" was the thesis.
- Breakout entry above resistance → stop back inside the old range.
- Never tighten a stop to afford a bigger position — size derives from stop distance, never the reverse.
Placing stops inside obvious noise levels is the classic self-defeat: stopped out on a wick, watching the original thesis play out without you.
The mistakes that make stops fail#
- No stop "because I'll watch it." Screens freeze; denial doesn't. Manual stops are hopes with extra steps.
- Moving the stop away as price approaches it. The moment you widen a stop, planned risk becomes negotiable — and negotiable risk grows until it ends accounts. The stop moves toward profit only, never away.
- Mental stops only. Same as no stop, with extra keystrokes of false comfort.
- Ignoring gap risk on instruments prone to overnight jumps — size positions assuming fills worse than trigger.
Why professionals treat stops as sacred#
A stop-loss converts every trade into a bounded experiment: risk exactly −1R to test a hypothesis with defined positive expectancy (Part 3). Without it, one trade carries unbounded downside capable of erasing twenty good decisions. Survival arithmetic — not conservatism — makes the stop-loss the first order placed on every professional ticket, not the last.
Related series: risk management math · where stops fit each strategy · what is VWAP
