IV Rank converts an absolute IV reading into a relative one. A 25% IV in a security that normally trades at 60% IV is high; a 25% IV in one that normally trades at 15% is low. IV Rank captures that context with a single 0-to-100 figure.
IV Percentile, a closely related metric, reports the fraction of days in the last year where IV closed below the current level. Both are widely used in options selling strategies — premium sellers prefer high IV Rank / IV Percentile because it implies the options being sold are richly priced relative to history.
IV Rank = (IV − IV_52w_low) / (IV_52w_high − IV_52w_low)How ChartGEX uses it
ChartGEX feeds IV Rank into the ML feature vector and surfaces it on the volatility view. It is one of several inputs into the vol regime classification (low, medium, high) that conditions dealer-structure detection thresholds.