Indicators
ATR and Bollinger Bands: measure volatility before risk
Use ATR and Bollinger Bands to describe range and dispersion, recognize volatility changes, and avoid confusing volatility with direction.
By atradeaday · Published
Volatility measures help answer how much prices are moving. They do not independently answer which way prices will move next. This makes them useful inputs to trade planning and risk sizing, while leaving direction to a separately defined hypothesis.
Average True Range
True range is the largest of the current high minus low, the absolute high minus previous close, and the absolute low minus previous close. ATR smooths that series, commonly over 14 periods. Because it incorporates the previous close, it can reflect gaps that the candle's high-low range alone misses.
Fidelity's ATR guide explains this non-directional measure. A rise in ATR can accompany either a rally or a selloff.
For a hypothetical instrument at 100 with an ATR of 2, a two-ATR distance is 4 price units. That is a volatility reference, not a maximum possible loss. Gaps and poor liquidity can produce larger moves and worse execution.
Bollinger Bands
Bollinger Bands conventionally surround a moving average with bands based on a multiple of recent standard deviation. A common configuration uses a 20-period average and two standard deviations. The bands expand and contract as the measured dispersion changes.
Touching the upper band does not require an immediate fall. Narrow bands describe recent compression; they do not determine breakout direction or timing. See Fidelity's Bollinger Bands guide for the definition and standard interpretation.
Do not assume two standard deviations imply a reliable 95% future containment range. The indicator describes a rolling price sample, not a calibrated forecast distribution.
Connect volatility to sizing
Suppose a hypothetical risk budget is 40 currency units. A four-unit stop distance permits 10 units of exposure before costs; an eight-unit distance permits five. Keeping the same size while doubling the stop distance doubles the planned price risk.
Choose the invalidation from the trade idea, check whether ordinary volatility makes that location plausible, then size the position. Moving the stop closer merely to fit a desired size changes the strategy.
What to test
Compare fixed-distance and volatility-adjusted rules over distinct market conditions. Keep the ATR or band settings fixed within each test, include transaction costs, and record gap losses separately. A volatility measure trained on a quiet window may react too slowly to a sudden event.
Continue with position sizing and event risk.