Stop Order
A dormant order that becomes a market order once price reaches a trigger level.
Also called: stop market order · stop market
Written by Javier Sánchez Ros
In plain language
A stop order does nothing until the market touches its stop price. At that moment it converts into a market order and takes the best price available.
That conversion is the important detail. The stop price is where the order wakes up, not where it fills.
Stop orders work in both directions. A sell stop below the market protects a long position; a buy stop above the market protects a short, or triggers a breakout entry.
Worked through
A stop at $92 on a stock that gaps to $88.10
- Stop trigger
- $92.00
- Previous close
- $95.40
- Next open
- $88.10
- Loss against plan
- $3.90 per share worse
The stop worked exactly as specified. $92 was never traded — the stock closed at $95.40 and opened at $88.10 — so the order was triggered by the opening print and filled there, because a stop order becomes a market order the moment its level is passed.
That is the distinction the word "stop" hides. It is a trigger, not a price. It guarantees you will be taken out; it guarantees nothing about where.
Most of the time the difference is a cent or two and nobody notices. It matters on gaps, on news, and in fast markets — which is to say, precisely in the conditions the stop was bought for.
The practical answer is not to abandon stops, which is the wrong lesson. It is to size positions so that a gap of the size this instrument actually produces is survivable, and to know that overnight and weekend risk is not covered by any order type.
Why it matters
Understanding that a stop is a trigger rather than a guaranteed price is the difference between a risk model that holds up and one that fails in the exact conditions it was built for.
Common mistakes
- Believing the fill will match the stop price during a fast move or an overnight gap.
- Placing stops at obvious round numbers where many other stops cluster.
- Using a stop order in an illiquid instrument where the resulting market order fills badly.
Keep exploring
These concepts are connected. Understanding one usually makes the next one easier.
A predefined exit that closes a losing trade before the loss becomes serious.
A stop order that becomes a limit order instead of a market order when triggered.
The difference between the price you expected and the price you actually got.
A jump between one period’s close and the next period’s open with no trading in between.
An instruction to buy or sell immediately at the best price currently available.