Options skew is the difference in implied volatility (IV) across strike prices at the same expiration date. In SPX, out-of-the-money puts consistently carry higher IV than out-of-the-money calls at the same distance from the current price. This is called negative skew (or put skew), and it is one of the most persistent structural features of equity options markets.
Why Does Skew Exist?
The primary driver is demand for downside protection. Institutional investors and portfolio managers routinely buy OTM puts to hedge against market drawdowns. This elevated demand bids up put prices — reflected as higher implied volatility on the put side of the options chain.
On the call side, fewer participants systematically buy OTM calls for protection, so OTM calls tend to carry lower IV.
The result: on a skew chart that plots IV by delta, you will see IV rising steeply as you move toward lower strikes (deeper OTM puts), while IV on the call side remains relatively flat or gently declining. For how dealer positioning amplifies this structural demand, see how institutional gamma data can improve iron condor setups.
How to Read a Skew Chart
A standard skew chart places the delta (or strike) on the x-axis and implied volatility on the y-axis. Key observations:
- High skew: The put side IV is significantly higher than the call side. Puts are expensive relative to calls.
- Low skew: The put/call IV differential has compressed — markets are calmer or there is less demand for downside protection.
- Flat skew: Unusual; often seen briefly after a sharp market selloff when fear is already elevated across all strikes.
How Skew Affects Iron Condors
For iron condor traders, skew has a direct practical effect. Because OTM puts carry higher IV than OTM calls at the same delta, the put spread side of an iron condor naturally collects more premium per delta unit than the call spread side.
A symmetric iron condor — same delta on both put and call sides — is not truly symmetric in premium terms. The put spread contributes disproportionately more to total credit collected.
Adjusting for Skew
Systematic traders can account for skew in two ways:
- Accept the asymmetry: Use the same delta on both sides and acknowledge that the put spread provides more premium. This is the simplest approach and works well in most market environments.
- Normalize by adjusting deltas: Use a slightly wider (higher delta) call spread and a slightly narrower (lower delta) put spread to equalize the credit collected from each side. This reduces the put spread's outsized contribution.
Neither approach is universally superior — it depends on your risk tolerance for put-side vs. call-side exposure. For the related concept of put skew and how it interacts with iron condor selection, see what is put skew and iron condor selection.
Skew as Background Context
For systematic iron condor traders, skew is best understood as background context rather than a primary trading signal. You do not need to constantly monitor skew to execute a rules-based iron condor strategy. However, understanding that put skew exists explains why:
- Your iron condors typically collect more premium on the put side
- SPX put spreads are structurally more expensive than equivalent call spreads
- Your breakeven points are not mirror images of each other around the current price
Tradematic is an automated iron condor trading platform that incorporates this market structure awareness into systematic execution, so traders maintain consistent rules without manually adjusting for skew on every trade. The CBOE's volatility indexes and skew data provide real-time context for monitoring current skew conditions.
Comparison: High Skew vs Low Skew Environments
| Condition | Put IV vs Call IV | Effect on Iron Condor |
|---|---|---|
| High skew | Puts much more expensive | More premium collected on put side |
| Normal skew | Moderate put/call IV differential | Balanced premium collection |
| Low skew | Put/call IV near equal | More symmetric iron condor |
Frequently Asked Questions
Does skew change over time? Yes. Skew fluctuates with market conditions. It typically spikes during market stress and compresses during calm, trending markets.
Should I avoid trading iron condors when skew is very high? Not necessarily. High skew means more put premium, but also signals elevated fear. Your IVR filter is a more reliable entry gauge than skew alone.
Does skew affect both SPX and SPY? Yes, both exhibit negative skew. SPX typically shows slightly more pronounced skew due to its index composition and institutional hedging activity.
Can I measure skew easily as a retail trader? Yes. Most options chains show IV by strike. Compare the IV of an OTM put at 16-delta to the IV of an OTM call at 16-delta in the same expiration. The difference is your current put/call skew at that delta.
Does the 60/40 premium asymmetry from skew persist over time? Yes. SPX put skew is one of the most persistent features of equity index options markets. The put side has carried higher IV than the call side consistently for decades, driven by persistent institutional demand for downside protection.
Conclusion
Options skew is a structural feature of equity index markets driven by demand for downside protection. For iron condor traders, the practical implication is that put spreads collect more premium per delta than call spreads. Understanding skew helps set realistic expectations about your position's asymmetry — but it does not require constant manual adjustment in a systematic strategy.
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Trading involves risk and losses can occur. Past performance does not guarantee future results. Options trading is not suitable for all investors. Only allocate capital you are comfortable risking.
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