Acceleration Bands: Width From the Bar
Acceleration Bands place an envelope around a moving average using each bar's own high-low range as the scaling factor rather than the standard deviation of closes. The result reacts to a change in bar width one bar sooner than a deviation-based band does.
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How it works
Acceleration Bands wrap an envelope around a moving average. What makes them their own indicator is where the width comes from — each bar’s own high and low, not the spread of closing prices.
Each bar’s high is scaled up and its low scaled down by a factor derived from the bar’s range relative to its midpoint, and those scaled values are then smoothed into the upper and lower bands.
The practical difference is timing. A Bollinger Band widens only after the larger closes have entered its deviation window; a range-scaled band widens on the bar that was wide.
What it is used for
The rule as published is a two-bar confirmation. Price closing outside the upper band for two consecutive bars is treated as the start of a move rather than a single excursion.
The width itself is the more useful output. Any envelope’s separation is a volatility measurement, and reading it directly is often more informative than watching for touches.
Say a stock’s 14-bar average true range sits at $0.40 in a quiet month and $1.20 in a busy one — a threefold change in how far an ordinary bar travels.
That spread is the argument for adaptive bands of any kind. A fixed envelope sized for the middle, $0.80, is too tight in the busy month and too loose in the quiet one, and a real market spends much of its time nearer one of those states than the middle.
In practice
Nothing in the calculation reads volume. A wide bar on no participation widens the bands exactly as much as one on heavy trading, and only one of those is a genuine expansion.
The smoothing length is measured in bars, so a 20-period setting on a five-minute chart and on a daily chart are completely different instruments with one label.
A gap is the one case a range-based band handles badly. The gap itself is not inside any bar’s high-low range, so the bands widen only once a wide bar prints — after the event.
Using the opposite band as a stop is common and very loose. It is a wide exit that needs a correspondingly small position size, and that adjustment is the part usually left out.
Band-touch systems are high turnover. Each trade pays the spread and commission going in and again coming out, and touches are frequent by construction.
No participant is defending a band. Unlike a prior high, the level is arithmetic — which is the reason a touch alone has never been a sufficient signal in any envelope system.
How it sits in the envelope family
Three envelopes cover almost every variation and they differ only in what sets the width. Bollinger Bands use the standard deviation of closes. Keltner Channels use the average true range. Acceleration Bands use each bar’s own high-low range scaled by its midpoint.
Those three inputs disagree most in exactly the conditions that matter. Deviation of closes stays narrow through a session of wide bars that all close in the same place; a range-based measure does not. Knowing which input your envelope uses explains its behavior better than any parameter, and it is the first question to ask about any band you have not built yourself.
One more property separates a range-based band from a close-based one, and it shows up on the day it matters. A session of very wide bars that all close near the same level produces almost no deviation of closes and a large amount of range. The deviation band stays narrow through it; the range band widens.
Which of those is correct depends entirely on what you are using the band for. For a mean-reversion rule the closes are the relevant series, because that is where price keeps settling. For a stop distance the range is, because that is what price is capable of doing inside a bar.
What acceleration bands are not
They are not Bollinger Bands. Different width input, different behavior.
They are not a probability. No distribution is assumed or implied.
They are not a signal on their own. The published rule needs two bars.
And they are not adaptive to participation. They read price width only.
How this connects
This is one of a family of envelopes drawn around price. Bollinger bands use standard deviation, Keltner channels use average true range, and these use a fraction of the bar’s own range.
All three answer the same question differently. How far from a moving average is far enough to be unusual - and each measures “unusual” with a different yardstick.
The width is a volatility reading. Bands narrowing means recent ranges shrank; widening means the opposite. That is the same information an ATR gives, drawn on the price scale instead of below it.
A touch is not a signal. In a trend price can ride a band for many bars, which is why a breakout read from band contact alone produces so many false starts.
And the band you compare against is still a moving average, so everything true of that line - the lag, the arbitrary period - is true here too.
When it fails
In a range both bands get touched repeatedly and every touch looks like the start of something. A breakout rule applied there produces a steady sequence of round trips against a market that ends the period where it began.
The second failure is the two-bar rule in a fast market. Two closes outside the band can be most of the move, so the confirmation that removes false starts also removes the good entries.
A third is treating a touch as a level. Nothing rests there.
A fourth is running it beside a Bollinger Band as confirmation. Two envelopes computed from overlapping inputs agreeing is not independent evidence.
And a fifth is leaving the smoothing at a default. The length sets how quickly the bands respond, and it deserves the same attention the multiple gets on any other volatility tool.
The original data
Real volatility arrives in bursts, and the S&P 500 record shows how often. Between 1950 and 2026 the index had 68 separate spells closing 5% or more below its record, about 0.89 a year, and the worst ran from 9 Oct 2007 to 9 Mar 2009 for a fall of 56.8%. A band width calibrated in the calm years between those spells is far too narrow for the months inside them.
Smoothing is the trade-off hiding inside every band. Say one day’s range jumps to $2.00 where the 14-bar average was $0.80: a simple average of the last 14 bars rises only about $0.09 that day, which is what makes a smoothed band usable and also what makes it late. Decide which of those two properties your method needs before choosing a band — a breakout system wants the responsiveness and a mean-reversion system wants the stability, and no single setting delivers both.
Related
Bollinger Bands are the deviation-based envelope. Keltner Channels use average true range instead. And breakout is the event these bands were built to identify.
What matters is not which envelope you pick but that you know what sets its width. Deviation bands, range bands and fixed-percentage bands behave differently in exactly the conditions where you most need to trust them. Learn the family before settling on one member of it.
— Michael Whitman
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