Vol skew curve

What is vol skew?

Vol skew (also called volatility smile, smirk, or skew curve) is the shape of implied volatility plotted against option delta or strike. For a single expiration, plotting IV at 10Δ put / 25Δ put / ATM / 25Δ call / 10Δ call reveals the market's asymmetric pricing of upside vs downside risk.

In equity index options (SPY, QQQ, IWM), the standard shape is downside skew: out-of-the-money puts trade at higher IV than out-of-the-money calls. This reflects the reality that stock markets tend to crash faster than they rally, so market-makers demand more premium to sell OTM puts than OTM calls.

Reading the skew curve

Downside skew (typical for equities)

Left side of chart (put wings, higher deltas represent further OTM puts) is elevated. Right side (call wings) is flat or lower than ATM. Risk reversal (25Δ put IV − 25Δ call IV) is positive.

• Interpretation: Market prices asymmetric downside fear. Common in SPY/QQQ regardless of regime.
• Trade implication: Selling OTM puts often over-collects premium relative to realized moves. Buying OTM puts costs more than model-fair value.

Upside skew (rare, sometimes cryptos/momentum)

Right side of chart (call wings) elevated relative to put wings. Risk reversal is negative.

• Interpretation: Market prices asymmetric upside fear (fear of missing out on a squeeze). Common in COIN, MSTR, meme stocks during momentum bull phases.
• Trade implication: Selling OTM calls over-collects relative to realized. Buying OTM calls is expensive.

Flat / smile (rare in equities)

Both wings elevated symmetrically vs ATM. Common in currency and rates markets. In equities, appears during earnings weeks when both directions have material risk.

Key skew metrics

Risk Reversal (25Δ)

The workhorse skew metric: RR25 = IV(25Δ put) − IV(25Δ call). Positive = downside skew. Negative = upside skew. SPY 25Δ RR typically runs +2 to +6 vol points in normal markets, spiking to +10-15 during panics.

Put skew (25Δ − ATM)

How much extra premium the market prices into 25Δ puts vs ATM. Higher = more downside fear.

Call skew (25Δ − ATM)

Usually negative (calls are cheaper than ATM in equities). If it turns positive, the market is pricing significant upside risk.

How to trade with skew awareness

For CSP sellers

Higher put skew = richer premium on your CSPs. But it also means the market expects more downside than usual. Use it as a signal: when SPY 25Δ RR > +8 vol points, be more selective about CSP entries.

For CC sellers

Downside skew means OTM calls are relatively cheap (in vol terms). Selling OTM calls in normal skew regimes underperforms relative to selling ATM calls in vol terms. Consider staying closer to ATM.

For iron condor traders

In steep-skew regimes, the natural iron condor width is asymmetric: put wing wider than call wing to reflect the higher put IV. Symmetric strikes leave alpha on the table.

Regime detection

Watching risk reversal shift day-to-day is a leading indicator of sentiment. Sharp jumps in RR25 (positive spikes) often precede or accompany selloffs. Sharp drops (RR25 flattening) often precede reliefs.

How it's calculated

For each target delta (0.10, 0.25, 0.40, 0.50):

1. Fetch the option chain snapshot for the selected expiration from Polygon.io.
2. Filter to contracts with valid gamma, IV, and open interest.
3. Sort by absolute distance from target delta.
4. Take the closest contract's IV as the skew point.
5. Repeat for both puts and calls.

ATM IV is computed as the average of 50Δ put IV and 50Δ call IV. Risk reversal is (25Δ put IV) − (25Δ call IV). All IVs are annualized as returned by Polygon.

Related tools

• Term Structure Curve — complementary chart of ATM IV vs DTE.
• IV Rank Leaderboard — vol regime metric per ticker.
• Expected Move — ATM straddle-based ±1σ envelope.
• Gamma Exposure — dealer positioning that shapes skew via hedging flow.
• Vol Skew glossary — canonical definition with worked example.

Data source: Polygon.io options snapshots. Methodology on the methodology page. Educational only.