The moving average part
The middle line of a Bollinger Band is almost always a 20-day simple moving average (SMA), the arithmetic mean of the last 20 closing prices, recalculated every day as the window rolls forward. This line is the same thing you would get from any moving average study. It smooths out daily noise and shows the general level the price has been trading around over the past month of sessions.
The standard deviation part
The bands themselves come from standard deviation, a statistical measure of how far individual values sit from their average. Take the same 20 closing prices used for the SMA, work out how far each one sits from that average, and standard deviation gives you a single number summarising that spread. A tight, calm price series produces a small standard deviation. A share whipping up and down produces a large one.
John Bollinger's original construction plots the upper band at the 20-day SMA plus two standard deviations, and the lower band at the 20-day SMA minus two standard deviations. Nothing in that formula asks where the price is headed. It only asks how dispersed the last 20 closes have been.
What a touch of the band actually tells you
Because the bands are set at a fixed statistical distance from the average, a touch of either band is simply price reaching an unusual distance from its own recent mean, given how volatile it has been. That is a volatility observation, not a forecast. When volatility is low, the bands sit close together, and even a small price move can push the close up against one of them. When volatility is high, the bands widen, and price can push hard in one direction while staying inside them the whole time.
This is why "riding the band" can happen in trending markets. A share in a strong uptrend can close at or above its upper band for session after session, because the average is dragging upward with it and volatility stays elevated in the same direction. Anyone selling on the first touch in that scenario is fading a trend, not calling a top.
A worked example
Take a hypothetical stock trading at ₦50, with a 20-day SMA of ₦48 and a 20-day standard deviation of ₦1. The upper band sits at ₦48 + (2 x ₦1) = ₦50, and the lower band at ₦48 minus ₦2 = ₦46. At ₦50, the price is already touching the upper band. If the next day's close is ₦51, and the average and deviation shift only slightly, the band itself moves up too, because it is recalculated from the same rolling 20 closes. The stock can keep closing near or above a rising upper band through several sessions of a genuine rally. Nothing about that sequence says the move is exhausted. It says the recent range has been narrow relative to the current push, which is a volatility fact, not a reversal signal.
What decides direction is somewhere else
Direction comes from price structure, volume, the trend of the underlying fundamentals, or other indicators built to read momentum rather than dispersion, such as the relative strength index or a moving average crossover. Bollinger Bands can tell you that a squeeze has formed, bands pulled unusually tight, which can precede a bigger move. What they cannot tell you is which way that move will break. Traders who combine a band touch with a separate momentum reading are, in effect, admitting the bands alone do not answer the direction question.
What this piece has not covered
This is a mechanics explainer, not a market call. It uses illustrative figures to show how the calculation works, not reported prices, standard deviations or band levels for any specific counter on the NGX, GSE or JSE. A reader wanting to see how a real share is sitting against its own bands needs to pull that chart directly rather than take a general rule of thumb from a worked example. The indicator's construction is fixed and well documented. How a specific stock is behaving against it, on any given day, is not something this explainer can answer without live data in front of it.
The practical takeaway is narrow but firm: a Bollinger Band touch describes how stretched a price is relative to its own recent volatility. It does not describe where that price is going next. Treating the two as the same thing is where the indicator gets misused.
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