Average True Range - ATR

What

Developed by J. Welles Wilder and introduced in his book, New Concepts in Technical Trading Systems (1978), the Average True Range (ATR) indicator measures a security's volatility. As such, the indicator does not provide an indication of price direction or duration, simply the degree of price movement or volatility.

How

More specifically, the average true range is the (moving) average of the true range for a given period. The true range is the greatest of the following:

• The difference between the current high and the current low
• The difference between the current high and the previous close
• The difference between the current low and the previous close

The average true range is then calculated by taking an average of the true ranges over a set number of previous periods. Care should be taken to use sufficient periods in the averaging process in order to obtain a suitable sample size, i.e. an average true range using only 3 periods would not provide a large enough sample to give you an accurate indication of the true range of the security’s price movement. A more useful period to use for the average true range would be 14

When

Extreme levels (both high and low) can mark turning points or the beginning of a move. As a volatility-based indicator like Bollinger Bands, the ATR cannot predict direction or duration, simply activity levels. Low levels indicate quiet trading (small ranges), and high levels indicate violent trading (large ranges). A prolonged period of low ATR readings might indicate consolidation and the beginning of a continuation move or reversal. High ATR readings usually result from a sharp advance or decline and are unlikely to be sustained for extended periods.