VIX Explained: What the CBOE Volatility Index Means for Options Traders

How the VIX Is Calculated

The VIX is derived from real-time bid/ask prices of a wide range of SPX options across multiple strikes — both puts and calls — for the two nearest expirations. The CBOE methodology aggregates these option prices to extract the market's expectation of future volatility without requiring specific model assumptions. The result is a forward-looking measure: the VIX is not based on what the market has done historically, but on what market participants are currently paying to hedge or speculate on future SPX moves over the next 30 days.

The key insight: VIX is derived from options prices, and options prices reflect implied volatility. High options premiums → high VIX. Low options premiums → low VIX. The VIX is essentially a real-time aggregated measure of the implied volatility of the SPX options market.

Converting VIX to Expected Daily and Weekly Moves

VIX is expressed as an annualized figure. To convert to a daily expected move (1 standard deviation):

Daily expected move (1 std dev) = VIX / √252 ≈ VIX / 15.87

At VIX 20: daily expected move ≈ 20 / 15.87 ≈ 1.26%. The S&P 500 is expected to move approximately ±1.26% on any given day with 68% probability (1 standard deviation).

For weekly expected moves (5 trading days): VIX / √52 ≈ VIX / 7.21. At VIX 20: weekly expected move ≈ 2.77%.

These expected move figures directly determine iron condor and credit spread strike selection — placing short strikes at 1–2 standard deviations from current price is the mechanical basis for defining "where the underlying is unlikely to reach" in any given options cycle.

VIX Regimes: What Different Levels Mean

VIX levels have historically clustered into regimes with different implications for options traders:

• VIX below 15 — low volatility regime: Complacency or genuinely calm markets. Options premiums are cheap. Premium sellers collect less absolute credit. Buyers can acquire options at lower cost. Historically, sustained very low VIX has preceded volatility regime changes — though the timing is unpredictable.
• VIX 15–25 — normal range: The VIX spends most of its time in this zone during normal market conditions. Options premiums are moderate. Standard premium selling strategies (iron condors, credit spreads, covered calls) generate reasonable income without excessive risk premium overpayment by buyers.
• VIX 25–35 — elevated volatility: Market stress or uncertainty. Options premiums are significantly elevated. Premium sellers can collect larger credits for the same strike distances, improving the risk/reward profile of income strategies. VIX at this level has historically been an above-average environment for selling options.
• VIX above 40 — crisis/spike territory: Extreme fear events (market crashes, macro shocks). Options premiums are very high but realized moves can be extreme. While the edge for premium selling in very high VIX is historically strong (options have tended to overprice realized volatility even in crises), position sizing and strike selection must account for the possibility of sustained extreme moves.

VIX Mean Reversion: The Core Premium-Selling Edge

The VIX is strongly mean-reverting. Unlike stock prices, which can trend indefinitely, the VIX always reverts toward a long-term mean (approximately 18–20 over its history). VIX spikes above 40 or 50 are followed by reversion to normal levels within weeks to months. VIX below 12 tends to be temporary before reverting upward toward the mean.

This mean-reversion is the foundation of the Volatility Risk Premium (VRP) — the statistical tendency for implied volatility (VIX) to be higher on average than realized volatility. The market consistently overpays for options relative to what volatility actually materializes. Options sellers capture this premium systematically by selling when IV is elevated and allowing the mean reversion to work in their favor.

Practically: when VIX spikes sharply — say, from 18 to 35 in a week — the probability that it will be lower in 30 days than it is today is historically high. This is the classic entry signal for premium selling: enter iron condors, credit spreads, or short strangles when VIX has spiked, because you are selling elevated implied volatility that is statistically likely to revert lower before your options expire.

VIX Term Structure: VIX vs VIX3M

The CBOE also publishes VIX3M (formerly VXV) — the 3-month implied volatility for SPX. The ratio VIX/VIX3M or the shape of the VIX term structure provides additional information:

• Contango (VIX < VIX3M, normal): Near-term implied volatility is lower than medium-term. The market is calm now but uncertain longer-term. This is the typical state — options sellers benefit from near-term contango by selling short-dated premium that is cheaper relative to longer-term expectations.
• Backwardation (VIX > VIX3M, stress): Near-term implied volatility exceeds medium-term. The market is pricing an acute near-term risk — a major event, earnings season, geopolitical risk. Backwardation signals elevated near-term uncertainty and often coincides with VIX spikes above 25–30.

Backwardation in the VIX term structure is one of the most reliable signals of a fear spike that will likely revert. When VIX flips from backwardation back into contango, it historically marks the peak of the fear episode and the beginning of options premium compression.

VIX and GEX: Complementary Volatility Measures

VIX measures market-wide implied volatility derived from SPX options prices — a demand-side measure (what people are paying for options). GEX measures dealer positioning derived from options open interest — a supply-side mechanical measure (what dealers must do to hedge their exposure). They are complementary:

• High VIX + negative GEX: the most dangerous combination — fear is elevated and dealer mechanics are amplifying moves. Both directional buyers (expensive but may profit from continuation) and sellers (high premium but high risk of breach) face difficulty.
• High VIX + positive GEX: transitioning environment — fear remains elevated but structural suppression is returning. This is typically the best entry for premium sellers: high extrinsic to collect + structural damping to protect short strikes.
• Low VIX + positive GEX: the calmest environment — cheap options and suppressed mechanics. Good for steady income strategies but low absolute premium collection.