A dynamic trailing stop is an order whose trigger price is not a fixed value, but a gap (in percentage or dollar amount) relative to the security’s current price. This is the definition used by the US market regulator, the SEC, in its investor bulletin on stop, stop-limit, and trailing stop orders, published on sec.gov. This permanent recalculation is what distinguishes a dynamic trailing stop from a classic fixed-price stop.
The principle: a gap that follows the market, not a fixed price
With a classic stop order, the trader sets a trigger price once and for all. With a dynamic trailing stop, it is the gap that is fixed, not the price. The SEC states it this way: “A trailing stop order is a stop or stop limit order in which the stop price is not a specific price. Instead, the stop price is either a defined percentage or dollar amount, above or below the current market price of the security”. Concretely, if you hold a long position with a trailing stop set 2 dollars below the price, that trigger price will rise with each new high, always staying 2 dollars away.
Why the price freezes as soon as the market reverses
The central feature of the dynamic trailing stop, the one that gives it its name, is asymmetric: the recalculation only works in one direction. The SEC specifies this explicitly: “As the price of the security moves in a favorable direction the trailing stop price adjusts or trails the market price of the security by the specified amount. However, if the security’s price moves in an unfavorable direction the trailing stop price remains fixed”. In other words, as long as the price rises (for a long position), the trigger price rises with it while keeping the same gap. As soon as the price falls, the trigger price stops moving and stays frozen at its last reached level, waiting for the market to touch it or to rise again.
Triggering is not a guarantee of execution price
A frequent confusion is believing that the stop price is the price at which the position will actually be closed. That is not the case. According to the SEC: “The stop price is not the guaranteed execution price for a stop order. The stop price is a trigger that causes the stop order to become a market order. The execution price an investor receives for this market order can deviate significantly from the stop price”. Once the stop price is reached, the order becomes a simple market order, executed at the price available at that moment. In a fast-moving market, the gap between the trigger price and the price actually obtained can be significant, and in a direction unfavorable to the trader.
A concrete implementation: the trailing stop limit at a broker
The principle described by the SEC is generic and applies to all brokers regulated in the United States. Its technical implementation, however, varies by platform. At Interactive Brokers, for example, the trailing stop limit variant works as follows, according to the TWS platform user guide: “Aux Price (Trailing Amt) – This value is subtracted from the bid price to continually recalculate the stop price, if the market price rises. Use the dropdown to choose Amt or %. The trailing percent is calculated off the current best bid/ask”. The trailing amount can therefore be expressed either as an absolute value or as a percentage, the latter being calculated from the current best sale price (bid) and purchase price (ask).
Another feature specific to this implementation: unlike a simple trailing stop, the initial stop price is not calculated automatically by the platform when the order is transmitted. The guide specifies: “Unlike a trailing stop order, the initial stop price is not automatically calculated by TWS when you transmit the order, since the stop price is needed to calculate the limit price or limit offset. The stop price is continually recalculated when the market price rises”. It is the trader who must enter this initial stop price, since it serves as the basis for calculating the associated limit price or limit offset.
What this text does not cover
This mechanism described by the SEC concerns security orders placed with brokers regulated in the United States. It does not, on its own, describe how a dynamic trailing stop works on a contract for difference (CFD) market or on Forex, where execution rules depend on the broker and local regulation. Likewise, the Interactive Brokers example illustrates one implementation among others: other platforms may recalculate the stop price under different terms, for example based on the last traded price rather than the bid price.
Frequently Asked Questions
Can a dynamic trailing stop move up and down freely?
No. According to the SEC, the trigger price only moves in the direction favorable to the trader. As soon as the market moves in the unfavorable direction, this price stays fixed at its last reached level; it never moves back down to follow a decline on a long position.
Does a dynamic trailing stop guarantee the exit price?
No. The stop price is only a trigger. Once reached, the order becomes a market order, and the price actually obtained can deviate significantly from the stop price, especially if the market moves fast at the moment of triggering.
Do you need to enter the initial stop price yourself?
It depends on the platform. In the trailing stop limit variant offered by Interactive Brokers, the initial stop price must be entered manually by the trader, since it serves as the basis for calculating the limit price. Other implementations may work differently.
Is the trailing amount always expressed as a percentage?
No. According to both the SEC and the Interactive Brokers guide, the trailing amount can be defined either as an absolute value (a fixed amount) or as a percentage of the current price. The choice depends on the trader’s preferences and the options offered by the platform.
To learn more about order mechanisms, you can read our articles on the exact difference between IOC and FOK orders, on how the OCO order works, or on the stop-loss trigger order and why it becomes a market order.