A stop loss feels like a promise: price hits that level, the trade closes there. But that's not what happens. A stop is a trigger. When price reaches it, the order converts to a market order and fills at whatever price is available.
In calm markets, the difference is a fraction of a pip. In fast ones, it can be many pips. News spikes, gaps and thin liquidity are the usual culprits. A 5 pip stop that fills at 12 pips of loss is not a platform glitch, it's the design.
Guaranteed stops exist at some brokers, usually at a premium or with a wider minimum distance. They promise the exact fill price, and the broker takes the slippage risk. Not many offer them for scalping, and the cost often makes tight scalps unworkable.
The practical effect: position size should be set assuming the stop might slip, not assuming it will fill perfectly. A little buffer in the risk calculation goes a long way.
How much slippage buffer gets added to risk calculations, if any?
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Stop losses become market orders
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