Bollinger Band


When it comes to technical analysis in the world of finance, there are numerous tools and indicators that traders and investors rely on to make informed decisions. One such tool is the Bollinger Band, which has gained popularity among market participants due to its ability to provide valuable insights into price volatility and potential trend reversals. In this article, we will explore the concept of Bollinger Bands, how they are calculated, and how they can be effectively used in trading strategies.

What are Bollinger Bands?

Bollinger Bands, developed by John Bollinger in the 1980s, are a widely used technical analysis tool that consists of a set of three lines plotted on a price chart. The middle line is a simple moving average (SMA), typically based on the closing price over a specified period. The upper and lower bands are calculated by adding and subtracting a certain number of standard deviations from the middle line.

The standard deviation is a statistical measure that quantifies the amount of price volatility or dispersion around the moving average. By using standard deviations, Bollinger Bands dynamically adjust to market conditions, expanding during periods of high volatility and contracting during periods of low volatility.

Calculation of Bollinger Bands

The calculation of Bollinger Bands involves three main steps:

  1. Calculate the middle band, which is typically a 20-day simple moving average (SMA).
  2. Calculate the standard deviation of the closing prices over the same period as the SMA.
  3. Calculate the upper and lower bands by adding and subtracting a certain number of standard deviations from the middle band. The most common value used is 2 standard deviations.

For example, let's consider a stock with a 20-day SMA of $50 and a standard deviation of $2. The upper band would be $54 ($50 + 2 * $2) and the lower band would be $46 ($50 – 2 * $2).

Interpreting Bollinger Bands

Bollinger Bands provide valuable information about price volatility and potential trend reversals. Traders and investors can interpret Bollinger Bands in the following ways:

1. Volatility

When the price is moving within the Bollinger Bands, it indicates a period of relatively low volatility. Conversely, when the price moves outside the bands, it suggests a period of increased volatility. Traders can use this information to gauge the potential for price breakouts or reversals.

2. Squeeze

A Bollinger Band squeeze occurs when the bands contract, indicating a period of low volatility. This often precedes a significant price move, as periods of low volatility are typically followed by periods of high volatility. Traders can watch for a squeeze and prepare for potential breakout trades.

3. Support and Resistance

The upper and lower bands of Bollinger Bands can act as dynamic support and resistance levels. When the price approaches the upper band, it may encounter resistance and reverse its direction. Conversely, when the price approaches the lower band, it may find support and bounce back up. Traders can use these levels to identify potential entry and exit points.

Using Bollinger Bands in Trading Strategies

Bollinger Bands can be used in various trading strategies to generate buy and sell signals. Here are a few common strategies:

1. Bollinger Band Breakout

Traders can look for breakouts when the price moves outside the bands. A breakout above the upper band can signal a bullish trend, while a breakout below the lower band can indicate a bearish trend. Traders can enter long or short positions accordingly and set stop-loss orders to manage risk.

2. Bollinger Band Reversal

When the price reaches the upper or lower band, it does not necessarily mean that a trend reversal will occur. However, if the price starts to reverse and move back towards the middle band, it can be a potential reversal signal. Traders can wait for confirmation, such as a candlestick pattern or a trendline break, before entering a trade.

3. Bollinger Band Width

The Bollinger Band width, which is the difference between the upper and lower bands, can be used to gauge volatility. When the band width is narrow, it suggests low volatility, while a wide band width indicates high volatility. Traders can use this information to adjust their trading strategies accordingly.

Case Study: Bollinger Bands in Action

Let's consider a real-life example to illustrate the effectiveness of Bollinger Bands in trading. Suppose we are analyzing the price chart of a stock and notice that the price has been consistently touching the upper band over the past few weeks. This indicates that the stock is in an overbought condition and may be due for a pullback.

As a trader, we decide to wait for confirmation before entering a short position. We look for a candlestick pattern or a bearish divergence on the relative strength index (RSI). Once we have confirmation, we enter a short trade with a stop-loss order above the recent swing high.

Over the next few days, the price indeed reverses and moves back towards the middle band. We decide to take partial profits and adjust our stop-loss order to breakeven. As the price continues to decline, we trail our stop-loss order to lock in additional profits.


Bollinger Bands are a powerful technical analysis tool that can provide valuable insights into price volatility and potential trend reversals. By understanding how to interpret Bollinger Bands and incorporating them into trading strategies, traders and investors can make more informed decisions and improve their chances of success in the financial markets.

Remember, Bollinger Bands are not a standalone indicator and should be used in conjunction with other technical analysis tools and risk management techniques. As with any trading strategy, it is important to backtest and validate the effectiveness of Bollinger Bands before applying them in real-time trading.

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