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Bollinger Bands are a tool of technical analysis which was invented by John Bollinger in the 1980s. Having evolved from the concept of trading bands, Bollinger Bands are an indicator that allows users to compare volatility and relative price levels over a period time. Basically, this tool provides a relative definition of high and low. By definition prices are high at the upper band and low at the lower band. This definition can aid in rigorous pattern recognition and is useful in comparing price action to the action of indicators to arrive at systematic trading decisions. When the market is calm, the Bollinger Band lines get closer together and when the market was changing Bollinger Band line expand. The indicator consists of three bands designed to encompass the majority of a security's price action:

1. A simple moving average in the middle
2. An upper band (SMA plus 2 standard deviations)
3. A lower band (SMA minus 2 standard deviations)


Standard deviation is a statistical unit of measure that provides a good assessment of a price plot's volatility. Using the standard deviation ensures that the bands will react quickly to price movements and reflect periods of high and low volatility. Sharp price increases (or decreases), and hence volatility, will lead to a widening of the bands.

For easier understanding, see the following chart: when the price was calm, Bollinger Band lines were close to one another, but when the price jumped up, Bollinger Band lines are spread. The same would happen if the price fell.



Calculation

• Upper = Average + 2*SD = X + 2*σ
• Middle = Average = X
• Lower = Average - 2*SD = X - 2*σ

Bollinger Bounce

The first thing you should know about Bollinger Band is that prices strive to return to the center of the Bollinger Bands. On the following chart you can see that the price has returned back towards the middle of Bollinger Bands.



What you just saw was a classic Bollinger Bounce. The reason why this “bounce” occurs is that Bollinger Band lines act like a level of support and resistance. The larger time period that you observe in the graph (H1, H4, D1), the stronger the Bollinger Bands get. Most traders developed systems that rely on the “jumps”. This strategy is best used when the market is in the range (ranging market) and while there is no clear trend.

Bollinger Squeeze

When the Bollinger Band lines get close together, it usually means that a break out will appear. If the candlesticks start to break out above the upper Bollinger Band line it is customary that the upward trend will continue, same thing is true for the downward trend.



If you look at the chart above you can see the Bollinger Band lines shrinking. Price is just beginning to penetrate upper Bollinger Bands lines and continues to go up. This is the way a typical Bollinger Squeeze works. This strategy is designed to catch a trend as soon as possible. This situation does not happen every day, but you can probably encounter it several times a week if you observe a 15 minute chart.

Interpretation

The use of Bollinger Bands varies wildly among traders. Some traders buy when price touches the lower Bollinger Band and exit when price touches the moving average in the center of the bands. Other traders buy when price breaks above the upper Bollinger Band or sell when price falls below the lower Bollinger Band.
When the bands lie close together a period of low volatility in stock price is indicated. When they are far apart a period of high volatility in price is indicated. When the bands have only a slight slope and lie approximately parallel for an extended time the price of a stock will be found to oscillate up and down between the bands as though in a channel.

As always, traders are inclined to use Bollinger Bands with other indicators to see if there is confirmation. In particular, the use of an oscillator like Bollinger Bands will often be coupled with a non-oscillator indicator like chart patterns or a trend line. If these indicators confirm the recommendation of the Bollinger Bands, the trader will have greater evidence that what the Bands forecast is correct.

Conclusion

Even though Bollinger Bands can help generate buy and sell signals, they are not designed to determine the future direction of a currency. The Bollinger Bands were designed to augment other analysis techniques and indicators. By themselves, Bollinger Bands serve two primary functions:

- To identify periods of high and low volatility
- To identify periods when prices are at extreme, and possibly unsustainable, levels

As stated above, currencies can fluctuate between periods of high volatility and low volatility. Being able to identify a period of low volatility can serve as an alert to monitor the price action of a currency. Other aspects of technical analysis, such as momentum, moving averages and retracements, can then be employed to help determine the direction of the potential breakout.

Remember that buy and sell signals are not given when prices reach the upper or lower Bollinger Bands. Such levels merely indicate that prices are high or low on a relative basis. A currency can become overbought or oversold for an extended period of time. Knowing whether or not prices are high or low on a relative basis can enhance our interpretation of other indicators, and it can assist with timing issues in trading.