Bollinger Bands

Yaser Rahmati | یاسر رحمتی

What are Bollinger Bands?

Bollinger Bands are a type of statistical chart characterizing the prices and volatility over time of a financial instrument or commodity. They were developed by John Bollinger in the 1980s and are used to identify overbought and oversold conditions, gauge volatility, and determine potential entry and exit points for trades.

Components of Bollinger Bands

1. Middle Band: This is a simple moving average (SMA), usually of 20 periods.

2. Upper Band: This is calculated by adding twice the standard deviation to the middle band.

3. Lower Band: This is calculated by subtracting twice the standard deviation from the middle band.

The formulae for Bollinger Bands are as follows:

• Middle Band (MB) = 20-period SMA

• Upper Band (UB) = MB + (2 * standard deviation)

• Lower Band (LB) = MB - (2 * standard deviation)

Components of Bollinger Bands

Calculating Bollinger Bands: Numerical Example

Let's consider a dataset of closing prices for a stock over 20 days.

1. Dataset of Closing Prices:

[100, 102, 101, 105, 107, 110, 112, 108, 107, 109, 111, 114, 115, 113, 116, 118, 119, 120, 122, 121]

1. Calculate the 20-day SMA (Middle Band):

MB = (100 + 102 + 101 + 105 + 107 + 110 + 112 + 108 + 107 + 109 + 111 + 114 + 115 + 113 + 116 + 118 + 119 + 120 + 122 + 121) / 20
   = 2115 / 20
   = 105.75

1. Calculate the standard deviation (σ):

deviations = [(price - MB)^2 for each price]
            = [(100 - 105.75)^2, (102 - 105.75)^2, ..., (121 - 105.75)^2]
            = [33.0625, 14.0625, 22.5625, 24.0625, 0.5625, 16.5625, 40.5625, 4.0625, 0.5625, 10.5625, 27.5625, 68.0625, 84.5625, 54.5625, 103.5625, 153.5625, 172.5625, 202.5625, 259.5625, 229.5625]
variance = sum(deviations) / 20
         = 1569.75 / 20
         = 78.4875
σ = sqrt(variance)
  = sqrt(78.4875)
  = 8.86

1. Calculate the Upper and Lower Bands:

UB = MB + 2σ
   = 105.75 + (2 * 8.86)
   = 105.75 + 17.72
   = 123.47

LB = MB - 2σ
   = 105.75 - (2 * 8.86)
   = 105.75 - 17.72
   = 88.03

How to Trade with Bollinger Bands

1. Overbought and Oversold Conditions:

• Overbought: If the price touches or exceeds the upper band, it may be considered overbought, suggesting a potential sell signal.

• Oversold: If the price touches or falls below the lower band, it may be considered oversold, suggesting a potential buy signal.

2. Price Breakouts:

• Breakout: When the price moves outside the bands, it indicates a strong momentum and could signal the beginning of a new trend. However, breakouts do not provide information about the direction and extent of the price movement.

3. Volatility Contraction and Expansion:

• Contraction: When the bands are narrow, it indicates low volatility and potential for a significant price movement.

• Expansion: When the bands are wide, it indicates high volatility and the potential for price consolidation.

4. Bollinger Band Squeeze:

• A squeeze occurs when the bands come close together, indicating a period of low volatility. This typically precedes a significant price movement.

5. Using Bollinger Bands with Other Indicators:

• Combining Bollinger Bands with other indicators like Relative Strength Index (RSI), Moving Average Convergence Divergence (MACD), or volume can enhance the effectiveness of trading signals.

Conclusion

Bollinger Bands are a versatile tool that can help traders identify potential overbought and oversold conditions, as well as periods of high or low volatility. By understanding and applying these bands properly, traders can make more informed decisions and potentially improve their trading performance.

Keywords

Bollinger Bands, technical analysis, stock trading, volatility, moving average, trading strategy, overbought, oversold, price breakout, market trends, standard deviation, financial indicators, trading signals, stock market, John Bollinger, یاسر رحمتی