Price tells you where a stock is. Volatility tells you how it is getting there — calmly or violently, predictably or erratically. Two tools dominate the practical measurement of volatility on charts: Bollinger Bands, which wrap a statistical envelope around price, and Average True Range (ATR), which distils the size of a typical bar into one number. They look different on a chart but answer related questions, and together they cover most of what a trader needs to know about a stock's temperament.
Why volatility deserves its own indicator
Two stocks can both close 2% higher and be in utterly different states. For one — a placid FMCG large cap that usually moves 0.7% a day — that 2% day is a three-sigma event worth investigating. For the other — a small cap that routinely swings 4% — it is a quiet Tuesday. Without a volatility yardstick you cannot tell these situations apart, and almost every practical trading decision depends on telling them apart:
- Position sizing — how many shares you can hold for a given rupee risk.
- Stop placement — a stop tighter than the stock's daily noise is a donation to the market.
- Signal interpretation — a breakout on a low-volatility stock means more than the same % move on a chronically jumpy one.
- Expectation setting — how much heat a position will plausibly generate before it works, if it works.
Bollinger Bands: a moving envelope
Developed by John Bollinger in the 1980s, Bollinger Bands consist of three lines:
1. A middle band — usually a 20-period simple moving average. 2. An upper band — the middle band plus two standard deviations of price over those 20 periods. 3. A lower band — the middle band minus two standard deviations.
Standard deviation is the key ingredient. It measures how widely closes have been scattered around their average. When price moves in a tight range, the deviation is small and the bands hug the average; when price swings hard, the bands balloon outward. The envelope therefore breathes with the stock — that is what separates Bollinger Bands from fixed-percentage envelopes.
What touching a band means (and doesn't)
Because roughly 95% of values in a normal distribution fall within two standard deviations of the mean, people leap to "price at the upper band = overbought = sell". That leap is wrong twice over. First, returns are not normally distributed — extreme moves happen far more often than the bell curve implies. Second, and more practically, in a strong trend price can ride a band for weeks. "Walking the band" — close after close pressed against the upper band — is a hallmark of powerful uptrends, not a reversal warning. The same applies inversely in downtrends.
A band touch is information, not instruction: it says price is at the outer edge of its recent range. Whether that means exhaustion or strength depends entirely on the trend context.
The squeeze: volatility's spring
The most celebrated Bollinger pattern is the squeeze: the bands contract to their narrowest width in months because price has gone unusually quiet. Volatility is strongly cyclical — quiet periods tend to be followed by loud ones and vice versa — so an extreme squeeze marks conditions where a large move has better-than-usual odds of starting soon.
Two caveats before anyone gets excited. The squeeze says nothing about direction — the expansion can break either way, and the first move is sometimes a head-fake against the eventual trend. And "soon" is elastic — squeezes can tighten further before resolving. Traders typically wait for the expansion itself (a close outside the bands with volume) rather than positioning inside the squeeze.
%B and bandwidth
Two derived readings make the bands screenable. %B locates the close within the envelope (1 = at the upper band, 0 = at the lower, 0.5 = at the middle). Bandwidth measures the gap between the bands relative to the middle — the squeeze detector. A screen for "bandwidth at a six-month low" is a systematic way to surface coiled springs across the whole market instead of eyeballing hundreds of charts.
ATR: the size of a typical bar
Where Bollinger Bands wrap around price on the chart, Average True Range reduces volatility to a single number: the average size of a day's true movement over a lookback window, commonly 14 days.
The clever part is the "true" in true range. A day's raw high-minus-low understates movement when price gaps. If a stock closes at 500 and opens the next day at 520, a quiet 520–522 session still represents a 22-point journey for anyone holding overnight. True range therefore takes the largest of: today's high minus low; the absolute gap from yesterday's close to today's high; and the absolute gap from yesterday's close to today's low. ATR averages that over the window.
Rupee ATR versus percentage ATR
Raw ATR is denominated in rupees, which makes cross-stock comparison meaningless — 20 points of ATR is enormous for a ₹300 stock and trivial for a ₹20,000 one. The fix is ATR%: ATR divided by price. A stock with ATR% of 1.2 typically travels about 1.2% a day; one at 4.5 is nearly four times as energetic. TaurEye's screener exposes exactly this normalised form as its ATR % filter, so a condition like "ATR% below 2" reliably means calm regardless of price level.
What ATR is used for
- Stops that respect the noise. A widely used technique places stops a multiple of ATR (often 2× to 3×) away from entry. The stop then adapts to each stock's temperament instead of imposing one arbitrary percentage on everything.
- Position sizing. Decide the rupees you are willing to risk, divide by the rupee distance of your ATR-based stop, and you get a share count that equalises risk across calm and wild stocks. This single habit does more for consistency than most indicator tweaks.
- Regime awareness. A rising 14-day ATR on an index tells you the whole tape has become more energetic — spreads widen, gaps grow, and yesterday's "safe" stop distances quietly become inadequate.
- Screening for temperament. Volatility is a preference. Some want movers ("ATR% above 4"); others want sleep ("ATR% below 2"). Neither is right — but mismatching your temperament to a stock's is how plans get abandoned mid-trade.
Using the two together
Bollinger Bands and ATR measure cousins of the same quantity (dispersion of price), so they usually agree — squeezing bands and falling ATR both say "quiet". Their value comes from their different vantage points:
- Bands give volatility a location. Price at the lower band after a long slide is a different situation from price at the upper band after a vertical rally, even at identical ATR readings.
- ATR gives volatility a unit. You cannot size a position or set a stop with band width; you can with rupees of typical daily travel.
A coherent workflow uses each for what it is: screen for conditions with bandwidth or ATR% (find squeezes, find calm stocks, find movers), read the context on the chart with the bands (trend, walking, mean reversion), then plan the trade mechanics with ATR (stop distance, position size).
A worked example
Suppose a mid cap has spent eight weeks in a tightening range around ₹840. Bandwidth is at its lowest since last year; ATR has drifted from 24 to 11 rupees (ATR% ≈ 1.3). One session, price closes at ₹868 — outside the upper band — on twice its average volume.
The squeeze has resolved upward. The bands begin expanding; ATR ticks up within days as bar sizes grow. A trader who takes the breakout might place a stop 2.5 × ATR below entry — about 28 rupees at the new ATR of 11-and-rising — and size the position so that those 28 rupees times the share count equals a pre-decided fraction of capital. Whether this particular breakout works is unknowable in advance; the process guarantees only that the risk was defined by the stock's own behaviour, not by hope.
Now run the counterfactual: the same close at ₹868, but with the bands already wide after a month-long rally and ATR at 30. That is not a squeeze resolution — it is a late-stage thrust in an already-loud trend, with triple the stop distance and a materially different risk profile. Identical price event; opposite volatility context. This is the distinction these tools exist to make visible.
Reading band shapes: M-tops and W-bottoms
Beyond squeezes and walks, John Bollinger himself emphasised pattern reading relative to the bands — the same price pattern means different things depending on where it forms in the envelope.
A W-bottom is a double bottom with a specific volatility signature: the first low pierces or touches the lower band, the bounce lifts price back toward the middle band, and the second low — even if it is lower in absolute price — holds inside the lower band. Price made a new low; volatility-adjusted price did not. That undercut-but-inside structure says selling pressure is exhausting relative to the stock's own recent dispersion, which is more information than the raw chart shape alone provides. Confirmation is conventionally the move through the middle band, or through the bounce high, on expanding volume.
An M-top mirrors it: the first high rides outside or at the upper band, the second high — often at a higher absolute price — stalls inside it. Strength is narrowing. Again, no single pattern is decisive; the pattern's value is that it normalises price action by volatility, exactly the adjustment human eyes fail to make when staring at raw candles.
The general principle is worth internalising: any signal is stronger or weaker depending on its position within the bands. A breakout that starts from the middle of the envelope has room to travel; one that starts already pressed against a band is stretched before it begins.
Volatility across the Indian market
A screening habit that pays for itself quickly: know the typical ATR% terrain of the market you trade.
- Index heavyweights and large caps commonly sit in the 1–2% ATR band. Their squeezes are subtle, their breakouts measured, and their liquidity means stops execute close to where you placed them.
- Quality mid caps typically run 2–3.5%. This is where many swing traders live — enough energy to pay for the trade, enough liquidity to exit mistakes.
- Small caps and news-driven names run 4% and beyond, with the added hazard that ATR understates their risk: circuit limits, gap opens and thin order books mean realised slippage can exceed anything the indicator promised.
- Regime shifts move the whole distribution. In stressed markets, index ATR% can double in weeks, and a filter like "ATR% below 2" that returned 800 stocks last quarter may return 200 today. Volatility screens are relative to their era — re-baseline your thresholds periodically instead of treating them as constants.
The practical use: set your screener's ATR% range to match both your holding period and your stomach, and let the filter enforce the discipline your enthusiasm won't. A positional investor has no business being surprised that a 6% ATR stock produced a 15% adverse week; the number was on the label.
Questions that come up
Which settings should I use for the bands? The 20-period, 2-standard-deviation default is the reference standard and the right starting point. Shortening the window makes the envelope twitchier; widening the deviation to 2.5 or 3 captures more extreme excursions only. Changing settings to make past signals look better is curve-fitting, not analysis.
Is a close outside the bands a signal by itself? No — statistically it happens regularly and in trends it happens persistently. It is a volatility event that demands context: fresh expansion out of a squeeze reads very differently from the fifteenth consecutive close hugging the band.
ATR or standard deviation — which is the better volatility measure? They usually agree, but ATR incorporates gaps (via true range) while close-based standard deviation does not. In a gap-prone market like India's — earnings nights, global overnight moves — ATR is the truer description of what a holder actually experiences.
Do the bands work on weekly charts? Yes, and weekly squeezes are rarer and more consequential than daily ones — they mark multi-month compressions that often precede a stock's defining move of the year. The trade-off, as always, is patience: weekly setups take weeks to resolve.
Common mistakes
- Selling every upper-band touch. In trends, band-walking is strength. Fading it mechanically has been one of the most reliable ways to fight — and lose to — a bull market.
- Using raw ATR across stocks. Always normalise to ATR% when comparing or screening.
- Setting stops inside the noise. A stop closer than about one ATR is odds-on to be hit by ordinary fluctuation, unrelated to whether the idea was right.
- Assuming a squeeze picks a direction. It forecasts energy, not sign.
- Forgetting volatility clustering. Loud days follow loud days. After a shock, ATR stays elevated for a while — position sizes calculated from last month's calm are too big for this month's storm.
A screening recipe to start with
If you want to put all of this to work tomorrow morning, here is a conservative three-step recipe using end-of-day data:
1. Find compression. Screen for stocks whose ATR% sits in the bottom of their usual range — say "ATR% below 2" — combined with a liquidity floor such as "volume above 100000" so the quiet you find is genuine rest, not neglect. 2. Demand an intact trend. Add "price above the 200-DMA" (and, stricter, "% vs 50DMA above 0"). Quiet consolidation within an uptrend is historically a far better hunting ground than quiet drift below a falling average — compression resolves in the direction of the prevailing trend more often than against it. 3. Wait for ignition. From the resulting shortlist, act only on the names that subsequently print a range expansion — a close beyond the recent consolidation with relative volume above 1.5× or 2×. The screen finds the springs; the expansion tells you one has released.
The philosophy embedded in the recipe: volatility filters select conditions, trend filters select direction of least resistance, and volume confirms participation. No step predicts anything — each simply stacks the situation a little further from randomness. Position sizing with ATR, as described above, then converts whatever happens next into a bounded, pre-accepted outcome rather than a surprise.
Putting the two to work
Volatility tools do not tell you where price is going; they tell you what kind of ride to expect and how to prepare for it. Bollinger Bands turn dispersion into a picture — squeezes, expansions, band-walks. ATR turns it into a number you can build stops and position sizes from. Learn to read the first and budget with the second, and most of the "surprises" in a trading month become things you had already measured.
You can screen for both in TaurEye — try ATR % filters in the Screener, and pair them with trend conditions like distance from the 50- and 200-DMA to separate quiet trends from quiet drifts.
Written for education, not as a recommendation. Volatility measured from history can shift abruptly and without notice; treat every statistic here as context, not certainty. A SEBI-registered adviser is the right person to consult before any market decision.