The true answer to that is trends last for as long as they last. It isn’t our job to know how long a trend lasts. It is our job to identify the trends, to capture part of the trend for a profit, and to get out before the trend comes to an end and reverses. Note that trends come in a number of varieties. There are both uptrends and downtrends, and even sideways trends. There are trends that last for 5 years or longer, trends that last for a year or less, and even trends that occur over a single trading session. That’s how long a trend lasts.