Options Skew Explained: What Volatility Skew Tells Traders
Deep dive into volatility skew, its causes, and how traders use it.
Options Skew Explained
Volatility skew refers to the pattern of implied volatility across different strike prices for options with the same expiration date. In a perfectly efficient market with normally distributed returns, all strikes would have the same implied volatility. In reality, they do not, and the shape of this skew curve reveals critical information about market expectations and positioning.
The Shape of Skew
**Put Skew (Negative/Reverse Skew):** In equity markets, out-of-the-money puts almost always trade at higher implied volatility than at-the-money options, which in turn trade at higher IV than out-of-the-money calls. This creates a downward-sloping curve from left to right. This is the dominant pattern for indices like the S&P 500 and most individual stocks.
The primary driver is demand for downside protection. Portfolio managers systematically buy puts to hedge long equity exposure. Since the 1987 crash, which demonstrated that markets can gap down dramatically, the demand premium for OTM puts has persisted.
**Call Skew (Positive Skew):** Some assets exhibit higher implied volatility in OTM calls than OTM puts. This is common in commodities with supply constraints (like crude oil or natural gas) and in heavily shorted or momentum stocks where explosive upside moves are priced in.
**Volatility Smile:** When both OTM puts and OTM calls trade at elevated IV relative to ATM options, the curve forms a smile shape. This is typical in currency markets and around binary events like earnings or FDA decisions, where large moves in either direction are expected.
### Measuring Skew
The most common skew measurement compares the implied volatility of a 25-delta put to a 25-delta call. A positive skew value (put IV > call IV) indicates more demand for downside protection. Traders also compare the 25-delta put IV to the ATM IV to isolate the put-specific demand premium.
The CBOE publishes the SKEW Index, which measures the perceived tail risk in S&P 500 returns. Higher SKEW values indicate greater perceived risk of a large downside move.
### Trading with Skew
**Mean Reversion:** When skew reaches extreme levels, it often reverts. Extremely steep put skew may indicate excessive fear, creating opportunities to sell expensive puts (via put spreads) with a statistical edge. Unusually flat skew can signal complacency, making put protection historically cheap.
**Event Trading:** Before binary events, skew shifts can telegraph market expectations. If call skew steepens ahead of earnings, it suggests options market participants are positioning for upside surprise. If put skew steepens, the market is bracing for disappointment.
**Risk Reversals:** A risk reversal trade (selling an OTM put and buying an OTM call, or vice versa) directly monetizes skew. When put skew is steep, selling OTM puts and buying OTM calls gives you a credit or minimal debit while maintaining upside exposure. This is a common institutional structure.
### Skew as a Sentiment Indicator
Changes in skew over time are often more informative than absolute levels. When put skew steepens rapidly, it signals a sudden increase in demand for protection—institutional hedging is accelerating. When put skew flattens, it suggests hedges are being unwound or demand for protection is declining, which is generally a bullish signal.
Cross-asset skew comparisons are also valuable. If SPX put skew is steepening while individual stock skew remains flat, it suggests macro hedging rather than stock-specific concerns. This distinction helps traders determine whether the fear is systemic or idiosyncratic.
Understanding skew gives traders insight into the market's true risk assessment, often revealing positioning and expectations that are not visible in price alone.
**Put Skew (Negative/Reverse Skew):** In equity markets, out-of-the-money puts almost always trade at higher implied volatility than at-the-money options, which in turn trade at higher IV than out-of-the-money calls. This creates a downward-sloping curve from left to right. This is the dominant pattern for indices like the S&P 500 and most individual stocks.
The primary driver is demand for downside protection. Portfolio managers systematically buy puts to hedge long equity exposure. Since the 1987 crash, which demonstrated that markets can gap down dramatically, the demand premium for OTM puts has persisted.
**Call Skew (Positive Skew):** Some assets exhibit higher implied volatility in OTM calls than OTM puts. This is common in commodities with supply constraints (like crude oil or natural gas) and in heavily shorted or momentum stocks where explosive upside moves are priced in.
**Volatility Smile:** When both OTM puts and OTM calls trade at elevated IV relative to ATM options, the curve forms a smile shape. This is typical in currency markets and around binary events like earnings or FDA decisions, where large moves in either direction are expected.
### Measuring Skew
The most common skew measurement compares the implied volatility of a 25-delta put to a 25-delta call. A positive skew value (put IV > call IV) indicates more demand for downside protection. Traders also compare the 25-delta put IV to the ATM IV to isolate the put-specific demand premium.
The CBOE publishes the SKEW Index, which measures the perceived tail risk in S&P 500 returns. Higher SKEW values indicate greater perceived risk of a large downside move.
### Trading with Skew
**Mean Reversion:** When skew reaches extreme levels, it often reverts. Extremely steep put skew may indicate excessive fear, creating opportunities to sell expensive puts (via put spreads) with a statistical edge. Unusually flat skew can signal complacency, making put protection historically cheap.
**Event Trading:** Before binary events, skew shifts can telegraph market expectations. If call skew steepens ahead of earnings, it suggests options market participants are positioning for upside surprise. If put skew steepens, the market is bracing for disappointment.
**Risk Reversals:** A risk reversal trade (selling an OTM put and buying an OTM call, or vice versa) directly monetizes skew. When put skew is steep, selling OTM puts and buying OTM calls gives you a credit or minimal debit while maintaining upside exposure. This is a common institutional structure.
### Skew as a Sentiment Indicator
Changes in skew over time are often more informative than absolute levels. When put skew steepens rapidly, it signals a sudden increase in demand for protection—institutional hedging is accelerating. When put skew flattens, it suggests hedges are being unwound or demand for protection is declining, which is generally a bullish signal.
Cross-asset skew comparisons are also valuable. If SPX put skew is steepening while individual stock skew remains flat, it suggests macro hedging rather than stock-specific concerns. This distinction helps traders determine whether the fear is systemic or idiosyncratic.
Understanding skew gives traders insight into the market's true risk assessment, often revealing positioning and expectations that are not visible in price alone.
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