Bollinger Bands, ATR and reading volatility

The indicators so far have tried to describe direction and momentum. This chapter is about a quieter, more fundamental property of price: volatility — how much it's moving around, regardless of which way. Understanding volatility well is arguably more valuable than any directional indicator, because volatility is what you actually feel in your account, it's what determines how big a position you can safely hold, and it's the input that the entire risk half of this module depends on.

Bollinger Bands: standard deviation, drawn on the chart

Bollinger Bands are three lines. The middle is a moving average (commonly a 20-period SMA). The upper and lower bands are placed a number of standard deviations away from that middle line — typically two. Standard deviation is just a statistical measure of how spread out recent prices have been: when price has been calm and tightly clustered, the standard deviation is small and the bands sit close to the middle line; when price has been wild, the standard deviation is large and the bands flare wide apart.

So Bollinger Bands are, quite literally, a moving average with a volatility-scaled envelope drawn around it. The bands breathe — narrowing when the market is quiet, widening when it's turbulent — and that breathing is the whole point. They're often described as containing 'about 95% of recent price action' when set at two standard deviations, but treat that figure as a rough rule of thumb, not a law: it assumes price is normally distributed, and markets have fatter, nastier tails than the bell curve admits. Price pokes outside the bands more often, and more violently, than the tidy statistics suggest.

The squeeze and the expansion

The genuinely useful behaviour of Bollinger Bands is the cycle between contraction and expansion. When the bands narrow tightly together — a squeeze — it means volatility has collapsed and price is coiling in a tight range. Markets don't stay quiet forever; periods of low volatility tend to be followed by periods of high volatility, and vice versa. A squeeze is therefore a heads-up that a big move may be brewing — energy is being stored. When price finally breaks out and the bands flare wide, that's the expansion: volatility has returned, often violently.

Notice what the squeeze does and doesn't tell you. It signals that a large move is becoming more likely — but it gives you no clue about direction. The coil can release upward or downward with roughly equal ease, and false breakouts (price stabs one way, then reverses hard) are common precisely because so many traders are crowded around the obvious breakout level. The squeeze is a statement about volatility regime, not a directional trade. Anyone selling you a 'squeeze buy signal' has invented a direction the indicator simply doesn't contain.

ATR: volatility as a number you can use

Average True Range (ATR) is the most practically important indicator in this entire module, and it's the least glamorous. ATR measures, on average over a window, how much a stock moves in a single period — its typical daily range, accounting for gaps. A stock with an ATR of ₹20 typically swings about twenty rupees in a day; a stock with an ATR of ₹2 barely twitches by comparison. ATR has no direction and no overbought/oversold lines. It's a pure, honest gauge of how much this thing moves.

That sounds dull until you realise it's the missing input behind sane risk-taking. How far away should your stop sit so you're not knocked out by ordinary noise? Some multiple of ATR. How big a position can you hold without a normal day's wobble blowing past your risk limit? A function of ATR. How do you compare the 'riskiness' of a sleepy largecap to a jumpy smallcap on the same footing? Normalise by ATR. The whole execution-and-risk discipline in the next sub-module leans on this one quiet number — which is why we introduce it here, among the indicators, but really treat it as a risk tool.

Sizing stops and positions with ATR

Here's the practical chain, which the execution chapter will formalise. First, ATR tells you a sensible stop distance — wide enough to survive normal volatility, placed using the stock's own movement. Second, once you know your stop distance in rupees, and you've decided the maximum rupees you're willing to lose on the trade, simple division tells you your position size: risk budget divided by per-share stop distance equals how many shares you can buy. Volatility, via ATR, is therefore the link between 'how much can this lose me' and 'how much should I buy'.

Volatility is a regime, not a signal

The deepest point in this chapter: volatility is a regime, not a signal. It doesn't tell you to buy or sell — it tells you what kind of environment you're operating in, and that should change how you behave. In a high-volatility regime, the same percentage stop gets hit far more often, position sizes must shrink, and 'normal' daily moves are large enough to shake out anyone sized for calm conditions. In a low-volatility regime, moves are small, stops can be tighter, and complacency creeps in just before volatility inevitably returns. Volatility also famously clusters: calm follows calm, storms follow storms, and the transitions can be abrupt. This is why treating a volatility indicator as a buy/sell trigger is a category error. ATR and the Bollinger squeeze are telling you about the weather system you're in, so you can dress appropriately — size down in storms, respect that a quiet market is storing energy. They are inputs to your risk decisions, not entries on a trade ticket. Get this right and you'll survive the regimes that wipe out traders who only ever watched direction.