The True Range Indicator is the greatest of the following: - Current high less the current low. - The absolute value of the current high less the previous close. - The absolute value of the current low less the previous close. "The average true range is a moving average (generally 14-days) of the true ranges".
ATR was originally developed for commodities but the indicator can also be used for stocks and indexes. Simply put, a stock experiencing a high level of volatility will have a higher ATR, and a low volatility stock will have a lower ATR.
Current ATR = [(Prior ATR x 13) + Current TR] / 14
ATR is not a directional indicator, such as MACD or RSI. Instead, ATR is a unique volatility indicator that reflects the degree of interest or disinterest in a move. Strong moves, in either direction, are often accompanied by large ranges, or large True Ranges. This is especially true at the beginning of a move. Uninspiring moves can be accompanied by relatively narrow ranges. As such, ATR can be used to validate the enthusiasm behind a move or breakout. A bullish reversal with an increase in ATR would show strong buying pressure and reinforce the reversal.
Technical chart for ATR