Forward-looking versus realized
The VIX is a forward-looking estimate of the S&P 500's expected volatility over the next thirty days, built from a model-free formula across the full range of strikes rather than a single option's implied volatility. It carries the crash-insurance premium embedded in far out-of-the-money puts. Realized volatility, sometimes shown as HV30, looks backward instead — the annualized standard deviation of the last thirty daily returns, what actually happened rather than what was priced.
The VIX trades above realized volatility roughly seventy to eighty percent of months — a persistent gap called the volatility risk premium, worth three to five volatility points on average. It is not a market inefficiency; it is rational compensation for underwriting crash risk. A simple shortcut for translating the VIX into an expected daily move: divide by sixteen.
The shape of the curve
Term structure plots at-the-money implied volatility across expirations. An upward-sloping curve — contango — reads as calm and normal; an inverted curve — backwardation — reads as near-term fear; a sharp kink at one date usually marks a single scheduled catalyst, an earnings report or a policy decision.
Skew plots implied volatility across strikes within one expiration. A normal put skew, where out-of-the-money puts carry richer volatility than calls, reflects steady demand for downside protection. A call skew, where the richness runs the other way, tends to show up in names prone to upside squeezes. A smile, where both tails are bid, prices binary risk in both directions at once. Put/call ratios — by volume for today's flow, by open interest for held positioning — round out the picture: readings above 1.5 or below 0.4 are read as contrarian extremes.
Reading volatility's own volatility
IV Rank places today's implied volatility between its own fifty-two-week low and high, as a percentage — a metric sensitive to a single outlier day, which can compress the whole scale. IV Percentile instead measures the share of days in the same window where volatility was lower than today, a rank rather than a range, and more robust to one extreme print. The two can disagree, and it is worth checking both before calling volatility cheap or rich.
Vol of vol measures how much implied volatility itself jumps around day to day, independent of its level — high vol-of-vol names see volatility spike and crush quickly, which matters to anyone holding a long-vega position through a binary event. IV dispersion measures how rough or smooth the volatility surface is across nearby strikes and expirations after accounting for the normal skew and term shape; high dispersion can mean thin liquidity, or genuine disagreement priced into nearby strikes.
Structure and sentiment
OI concentration measures how much open interest clusters at a handful of strikes rather than spreading thin — high concentration builds stronger, more reliable walls. Options liquidity, read from bid/ask tightness relative to price, tells you how much to trust the quote in the first place.
Two sentiment cross-checks round out the picture: the Fear & Greed Index, a zero-to-hundred composite score built from momentum, volatility, and options flow; and the VIX futures basis, where futures trading above spot — contango — reads calm and futures trading below spot — backwardation — usually accompanies acute stress.