A trailing stop order is an order whose trigger threshold moves automatically to follow the best price available in the market. You do not reposition it yourself: the system does, according to a rule you set in advance. But this tracking mechanism should not be confused with a guarantee of the execution price, and regulatory texts are explicit on this point.
The technical definition: a threshold that follows the best market price
The European text governing the order-counting method under MiFID II defines the trailing stop this way: it is a stop order whose trigger price changes according to the BBO (best bid and offer, meaning the best buy and sell limits displayed in the market). In practice, if the price moves in the direction favorable to you, the threshold moves with it, at a fixed distance you have defined. If the price reverses, the threshold stays frozen at its last position: it never moves back. This is what distinguishes the trailing order from the classic stop order, whose threshold is fixed once and for all when the order is placed.
What happens to the order once the threshold is reached
This is where the technical definition meets a constant warning from regulators. The Autorite des marches financiers notes that orders with a trigger threshold carry a boundary beyond which they turn into a market order: once the threshold is reached, the order is automatically activated and converted into a market order, with no price limit at all. The American broker regulator, FINRA, states the same rule directly: a trigger price is never a guaranteed execution price, since the stop order becomes a market order as soon as the threshold is touched, and intermediaries must then execute it fully and promptly at the prevailing market price.
In other words, the threshold that moves with the market only protects the moment the order triggers. It does not protect the price at which you will ultimately be executed.
A real case settled by the AMF ombudsman
This principle is not a theoretical nuance: it has been the subject of an actual mediation case. An investor, referred to as Mr. G in the case published by the AMF ombudsman, had placed two trigger-threshold orders set at 12.03 euros and 11.98 euros. He found that his orders had been executed at a price of 11.42 euros, while he believed the thresholds had not been reached. The case review showed that a first fixing had been set at 11.34 euros, before the actual execution at 11.42 euros. The ombudsman concluded that this outcome was not an anomaly: this type of order does not, by design, allow control over the execution price. The gap between the threshold the investor had set and the price he ultimately received was therefore not a malfunction, but the logical consequence of the rule itself.
The specific case of the trailing stop loss on CFDs
On CFDs, the mechanism follows the same logic but with vocabulary specific to each broker, and the generic trailing order used on equity markets should not be assumed, without verification, to be identical to the one offered on a CFD account. The execution policy of a CFD broker specifies, for example, that for a sell order at a target price, the trailing stop loss triggers when the best bid price becomes equal to or lower than the target price, and is then executed at the first available bid price on the price ladder corresponding to the order size at the time it is processed. This last point deserves close reading: it is not the target price that serves as the execution price, but the first available price once the order triggers, which can create a gap depending on liquidity at that moment.
In addition, the American regulator of the retail Forex market, the NFA, requires market makers to have written procedures on how price slippage is applied. It specifies that a broker who advertises no slippage must design its platform to execute a market order at the price displayed at the time of entry, and to execute a stop order at the displayed threshold price. This requirement shows that the absence of slippage is not the default standard: it is a commitment some brokers make explicitly, and one that should be verified in their published conditions rather than assumed.
What none of these sources document
It is worth being precise about the limits of what these texts cover. None of the sources consulted provides a statistic on how often a trailing stop order actually triggers during a trading session, nor on the optimal distance to set between the price and the trailing threshold. These parameters depend on the volatility specific to each instrument and on each broker’s policy, and no general rule published by a regulator quantifies them. Presenting a precise figure on this point would amount to inventing data that neither the AMF, nor FINRA, nor the NFA, nor the European text actually provides.
What this means for a trader in evaluation
For a trader going through a prop firm comparison, the distinction between trigger threshold and execution price has a direct consequence for risk management: a daily drawdown can be reached faster than expected if execution occurs at a less favorable price than the set threshold, particularly during a widened bid-ask spread. This is why it remains useful to compare this trailing order to the classic stop order and to the limit order, whose price-protection logic differs significantly.