Article ·
What a stop loss can and cannot do
A stop loss is one of the most useful tools in trading, and one of the most misunderstood. Here is what it really protects you from, and where its protection ends.
Almost every trader has heard the advice: always use a stop loss. It is good advice. But a stop loss is often treated as a safety net that catches every fall, and that belief can be expensive. Knowing exactly what a stop loss does, and what it does not, helps you use it properly.
What a stop loss is
A stop loss is an exit decided in advance. Before you enter a trade, you choose the price at which you will accept that you were wrong and close the position. If the market reaches that level, the stop is triggered and an exit order is sent.
In a rule-based strategy, the stop is part of the code. It is written before the market opens, and the system acts on it without hesitation.
What a stop loss can do
It takes the decision out of the moment. The hardest time to decide whether to exit is when a trade is going against you. Fear and hope both arrive at once. A stop decided in advance removes that argument.
It limits loss on a normal day. When prices move smoothly, a stop closes the position close to the level you chose. Most of the time, that keeps a single bad trade from becoming a large one.
It makes position sizing possible. If you know roughly where you will exit, you can decide how large a position should be before you take it. Without a stop, size is a guess.
It makes a strategy testable. Rules that always exit the same way can be tested across years of market data and compared over time. Rules that depend on how someone feels on the day cannot.
What a stop loss cannot do
It cannot stop a gap. If the market closes at one level and opens far away the next morning, there may be no trading at your stop price at all. The order is filled at the first available price, which can be much worse. Overnight news, global events and results can all cause gaps.
It cannot promise your exit price. In fast markets, or in option contracts with few buyers and sellers, the price can jump past your stop before the order is filled. This difference is called slippage. A stop sets when you try to exit, not the exact price you get.
It cannot fix a weak idea. A stop limits the damage of each losing trade. If the strategy itself has no edge, many small controlled losses still add up.
It can take you out just before a reversal. Markets often move sharply and then turn back. A stop that is too tight can close a position that would have recovered. This is the price of protection, and it is a normal part of trading with stops.
It cannot work if the system cannot reach the market. Stops depend on the platform, the broker, the exchange and an internet connection. If any of them has a problem at the wrong moment, the exit may be late or missed.
Stops in options are different
Option prices can move much faster than the index itself, especially close to expiry or around big events. A stop based on an option's price can trigger on a brief spike, while a stop based on the index level may react later. Neither is perfect. Each strategy has to choose, and that choice is part of its design.
How we use them
At Patni Capital Algo, stops are one layer of risk control, not the only one. Depending on the strategy, rules can include:
- a stop loss on each leg of a position;
- a stop on the whole strategy, and in baskets, on the whole basket;
- a scheduled time exit, so intraday positions are not left open by accident;
- hedges on overnight positions, which limit how much a gap can hurt.
None of these remove risk. Together, they make the worst cases smaller and more predictable than having no plan at all.
The takeaway
Use a stop loss, and set it before you enter. But treat it as a plan for an orderly exit, not a promise. Gaps, slippage and system problems are real, and trading in derivatives can lose money even when every rule is followed.