What They Are, and What They Tell Investors

A Bollinger Band® is a technical evaluation instrument outlined by a set of trendlines. They’re plotted as two commonplace deviations, each positively and negatively, away from a easy shifting common (SMA) of a safety’s value and could be adjusted to consumer preferences.

Bollinger Bands® was developed by technical dealer John Bollinger and designed to provide traders a better chance of figuring out when an asset is oversold or overbought.

Key Takeaways

  • Bollinger Bands® is a technical evaluation instrument to generate oversold or overbought indicators and was developed by John Bollinger.
  • Three traces compose Bollinger Bands: A easy shifting common, or the center band, and an higher and decrease band.
  • The higher and decrease bands are usually 2 commonplace deviations +/- from a 20-day easy shifting common and could be modified.
  • When the worth regularly touches the higher Bollinger Band, it might probably point out an overbought sign.
  • If the worth regularly touches the decrease band it might probably point out an oversold sign.

Understanding Bollinger Bands

Methods to Calculate Bollinger Bands®

Step one in calculating Bollinger Bands® is to compute the straightforward shifting common (SMA) of the safety, usually utilizing a 20-day SMA. A 20-day SMA averages the closing costs for the primary 20 days as the primary knowledge level.

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The subsequent knowledge level drops the earliest value, provides the worth on day 21 and takes the common, and so forth. Subsequent, the usual deviation of the safety value can be obtained. Commonplace deviation is a mathematical measurement of common variance and options prominently in statistics, economics, accounting, and finance.

For a given knowledge set, the usual deviation measures how far numbers are from a mean worth. Commonplace deviation could be calculated by taking the sq. root of the variance, which itself is the common of the squared variations of the imply.

Subsequent, multiply that commonplace deviation worth by two and each add and subtract that quantity from every level alongside the SMA. These produce the higher and decrease bands.

Right here is that this Bollinger Band® method:

BOLU = MA ( TP , n ) + m σ [ TP , n ] BOLD = MA ( TP , n ) m σ [ TP , n ] the place: BOLU = Higher Bollinger Band BOLD = Decrease Bollinger Band MA = Transferring common TP (typical value) = ( Excessive + Low + Shut ) ÷ 3 n = Quantity of days in smoothing interval (usually 20) m = Quantity of commonplace deviations (usually 2) σ [ TP , n ] = Commonplace Deviation over final  n  intervals of TP beginaligned &textBOLU = textual content MA ( textual content TP, n ) + m * sigma [ text TP, n ] &textBOLD = textual content MA ( textual content TP, n ) – m * sigma [ text TP, n ] &textbfwhere: &textual content BOLU = textual content Higher Bollinger Band &textual content BOLD = textual content Decrease Bollinger Band &textual content MA = textual content Transferring common &textual content TP (typical value) = ( textHigh + textLow + textClose ) div 3 &n = textual content Variety of days in smoothing interval (usually 20) &m = textual content Variety of commonplace deviations (usually 2) &sigma [ text TP, n ] = textual content Commonplace Deviation over final n textual content intervals of TP endaligned

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BOLU=MA(TP,n)+mσ[TP,n]BOLD=MA(TP,n)mσ[TP,n]the place:BOLU=Higher Bollinger BandBOLD=Decrease Bollinger BandMA=Transferring commonTP (typical value)=(Excessive+Low+Shut)÷3n=Quantity of days in smoothing interval (usually 20)m=Quantity of commonplace deviations (usually 2)σ[TP,n]=Commonplace Deviation over final n intervals of TP

What Do Bollinger Bands® Inform You?

Bollinger Bands® is a well-liked approach. Many merchants consider the nearer the costs transfer to the higher band, the extra overbought the market, and the nearer the costs transfer to the decrease band, the extra oversold the market. John Bollinger has a set of twenty-two guidelines to observe when utilizing the bands as a buying and selling system.

The Squeeze

The “squeeze” is the central idea of Bollinger Bands®. When the bands come shut collectively, constricting the shifting common, it’s referred to as a squeeze. A squeeze indicators a interval of low volatility and is taken into account by merchants to be a possible signal of future elevated volatility and attainable buying and selling alternatives.

Conversely, the broader aside the bands transfer, the extra doubtless the prospect of a lower in volatility and the larger the opportunity of exiting a commerce. These situations usually are not buying and selling indicators. The bands don’t point out when the change could happen or through which course the worth might transfer.


Roughly 90% of value motion happens between the 2 bands. Any breakout above or under the bands is important. The breakout will not be a buying and selling sign and lots of traders mistake that when the worth hits or exceeds one of many bands as a sign to purchase or promote. Breakouts present no clue as to the course and extent of future value motion.

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Instance of Bollinger Bands®

Within the chart under, Bollinger Bands® bracket the 20-day SMA of the inventory with an higher and decrease band together with the day by day actions of the inventory’s value. As a result of commonplace deviation is a measure of volatility, when the markets turn into extra risky the bands widen; throughout much less risky intervals, the bands’ contract.

Picture by Sabrina Jiang © Investopedia 2021

Limitations of Bollinger Bands®

Bollinger Bands® will not be a standalone buying and selling system however only one indicator designed to offer merchants with data relating to value volatility. John Bollinger suggests utilizing them with two or three different non-correlated indicators that present extra direct market indicators and indicators based mostly on various kinds of knowledge. A few of his favored technical strategies are shifting common divergence/convergence (MACD), on-balance quantity, and relative energy index (RSI).

As a result of Bollinger Bands® are computed from a easy shifting common, they weigh older value knowledge the identical as the newest, that means that new data could also be diluted by outdated knowledge. Additionally, using 20-day SMA and a pair of commonplace deviations is a bit arbitrary and should not work for everybody in each state of affairs. Merchants ought to alter their SMA and commonplace deviation assumptions accordingly and monitor them.

What Do Bollinger Bands® Inform You?

Bollinger Bands® offers merchants an thought of the place the market is shifting based mostly on costs. It includes using three bands—one for the higher stage, one other for the decrease stage, and the third for the shifting common. When costs transfer nearer to the higher band, it signifies that the market could also be overbought. Conversely, the market could also be oversold when costs find yourself shifting nearer to the decrease or backside band.

Which Indicators Work Greatest with Bollinger Bands®?

Many technical indicators work finest along side different ones. Bollinger Bands® are sometimes used together with the relative energy indicator (RSI) in addition to the BandWidth indicator, which is the measure of the width of the bands relative to the center band. Merchants use BandWidth to search out Bollinger Squeezes.

How Correct Are Bollinger Bands®?

Since Bollinger Bands® are set two use +/- two commonplace deviations round an SMA, we must always anticipate that roughly 95% of the time, the noticed value motion will fall inside these bands.

What Time Body Is Greatest Used With Bollinger Bands®?

Bollinger Bands® usually use a 20-day shifting common.

The Backside Line

Bollinger Bands® generally is a great tool for merchants for assessing the relative stage of over- or under-sold place of a inventory and supplies them with perception on when to enter and exit a place. Sure facets of Bollinger Bands®, such because the squeeze, work nicely for forex buying and selling. Shopping for when inventory costs cross under the decrease Bollinger Band® typically helps merchants make the most of oversold situations and revenue when the inventory value strikes again up towards the middle moving-average line.