Volatility Smile vs Skew: What's the Difference?

SPY's 25-delta put carries an implied volatility of 29.2%. The same-delta call sits at 16.7%. That's a 12.6 percentage point gap, and it tells you something that most options textbooks get wrong from page one.

Every introductory course draws a symmetric U-shape for implied volatility across strikes: out-of-the-money puts are expensive, ATM options are cheap, out-of-the-money calls are expensive. A clean, tidy curve. The problem is that real equity options chains haven't looked like that since October 1987. What you actually see when you pull up a live SPY chain is a steep slope on the put side and a declining line on the call side. That shape has a different name. It's called volatility skew, and understanding why it replaced the volatility smile tells you where the variance risk premium concentrates by strike.

What Is a Volatility Smile?

A volatility smile is what you get when you plot implied volatility against strike price and the resulting curve looks like a U. Both out-of-the-money puts and out-of-the-money calls carry higher IV than at-the-money options, creating roughly symmetric wings on either side of spot.

The smile was the dominant shape in equity options markets before October 1987 and remains common in currency markets today. Its existence reflects a straightforward reality: traders on both sides of the distribution want protection against large moves. In FX, a sharp appreciation of one currency is as damaging to one side of a trade as a sharp depreciation is to the other. Both tails carry real economic risk, so both tails get bid up.

Fischer Black observed in 1976 that option prices systematically deviated from the predictions of the Black-Scholes model, with out-of-the-money options carrying higher implied volatilities than the model suggested¹. The smile was the market's way of acknowledging what Black-Scholes assumed away: returns aren't normally distributed, jumps happen, and tails are fatter than a Gaussian bell curve allows.

The key feature of a true volatility smile is symmetry. Both wings are elevated. Both tails are priced for jump risk. The curve bends upward on both sides of the strike axis with roughly equal magnitude.

That's not what equity markets show today.

What Is Volatility Skew?

Volatility skew, sometimes called a volatility smirk, describes the pattern where implied volatility increases steeply for out-of-the-money puts while staying flat or declining for out-of-the-money calls. The curve doesn't form a U. It forms a tilted line that slopes downward from left to right, with a pronounced kink on the put side.

This shape became the permanent feature of equity options markets after the crash of October 19, 1987. Before that date, equity volatility surfaces looked closer to a smile. After the S&P 500 dropped 20.5% in a single session, the market collectively repriced downside risk and never went back.

Mark Rubinstein documented this shift in 1994, showing that the implied binomial trees extracted from post-crash option prices embedded a persistent fear of large downward moves that hadn't existed in the pre-crash data². The symmetric smile was gone. What replaced it was a structural asymmetry: OTM puts became permanently expensive relative to their call-side equivalents.

The distinction matters because it changes how you think about options pricing. A smile says "both tails are dangerous." Skew says "the left tail is where the real fear lives." And that fear has a price, one that premium sellers collect and premium buyers pay, every single day.

The Data Shows Skew, Not a Smile

Theory is useful. Data is better. Here's what SPY's options chain actually looks like at 27 DTE, using the April 10, 2026 expiration with SPY trading at $663.75.

[Chart 1: SPY IV by Strike (27 DTE, Apr 10 2026 expiry)] SPY implied volatility by strike, April 10 2026 expiration. IV climbs from 13.7% at the 5-delta call to 40.8% at the 5-delta put. Data: ThetaData via td-cli.

On the put side, IV rises from 25.1% at the money to 40.8% at the 5-delta wing. That's a 15.7 percentage point increase as you move further out of the money. On the call side, IV falls from 19.9% at the money to 13.7% at the 5-delta wing, a 6.2 percentage point decline.

This is not a U-shape. The put wing climbs. The call wing drops. If you drew this curve, it would look like a ski slope tilted from upper-left to lower-right, with the steepest gradient on the far left side where deep OTM puts live.

The asymmetry is the entire story.

Why Equity Skew Exists

On October 19, 1987, the S&P 500 fell 20.5% in a single trading session. No earnings miss, no credit event, no war. The crash emerged from portfolio insurance programs that triggered cascading sell orders, and the market gapped through levels that nobody had priced as realistic.

Before that day, equity options markets showed something closer to a smile. After it, the market permanently repriced the probability of extreme downside moves. The crash proved that left-tail events weren't theoretical, and the institutional memory of that proof has persisted for nearly four decades.

The demand side reinforces the shape every day. Pension funds, endowments, and mutual funds systematically buy OTM puts as portfolio insurance. This structural bid inflates put implied volatility whether or not the market delivers the moves those puts are pricing. On the supply side, dealers who sell those puts demand higher IV to compensate for the jump risk they're absorbing. The further out of the money the put, the more extreme the scenario it covers, and the higher the premium the dealer requires.

David Bates documented this dynamic in 2000, showing that the post-crash fear premium in S&P 500 futures options was not a temporary reaction but a permanent structural feature of the market³. And the market has validated that fear repeatedly. The 2008 financial crisis, the 2020 COVID crash, the tariff-driven selloff of April 2025, each event reinforced the lesson that left-tail risk is real, frequent enough to matter, and catastrophic enough to justify expensive insurance.

Volatility skew reflects genuine tail risk that has materialized multiple times within most traders' careers, not an inefficiency waiting to be arbitraged. Does the market overprice that risk on average? Yes, and that overpayment is what creates the variance risk premium. But the skew itself reflects genuine structural demand for downside protection.

The Skew Gradient: How Overpricing Accelerates

The relationship between delta and skew isn't linear. It accelerates as you move further from the money, and the acceleration tells you something important about where the variance risk premium concentrates.

Moving from ATM to 25-delta, the skew roughly doubles from 5.2 to 12.6 percentage points. From 25-delta to 10-delta, it jumps again to 20.3 points. And at 5-delta, the gap between put and call IV reaches 27.1 percentage points. Each step further out of the money adds more skew than the last.

This convexity in the skew gradient means that deep OTM puts carry disproportionate overpricing relative to their closer-to-the-money equivalents. A 5-delta put doesn't just cost more than a 25-delta put in absolute terms. It costs more per unit of probability it represents. The market charges a premium on top of a premium for the most extreme downside protection.

For premium sellers, that gradient is the map. It shows exactly where the richest implied volatility sits relative to what the market is likely to deliver.

Why Volatility Skew Matters for Options Traders

Volatility skew maps the spatial distribution of the variance risk premium across strikes, and understanding that distribution changes how you select strikes, size positions, and think about the source of your edge.

Consider a short strangle. The put leg at the 16-delta level carries an IV of roughly 31.7%, while the call leg at the same delta sits around 15.6%. The put side is generating more than twice the implied volatility of the call side, which means the put side is collecting a disproportionate share of the variance risk premium. When we sell a strangle, the put isn't just "the other leg." It's the primary source of the edge.

This has practical consequences. If you're choosing between selling a short strangle or an iron condor, the skew tells you which strikes offer the richest premium relative to their probability of being breached. Steeper skew means more VRP on the put side, which favors structures that emphasize put credit. Flatter skew means the premium is distributed more evenly, which might favor symmetric structures like a straddle.

Skew also works as a regime signal. When skew steepens beyond its normal range, the market is pricing elevated crash risk. That steepening can precede large moves, or it can simply reflect elevated hedging demand that creates opportunity for premium sellers willing to lean into it. When skew flattens, the market is relaxed about tail risk, and the richness of OTM puts compresses. Tracking the 25-delta skew over time gives you a real-time read on how the market is pricing directional fear.

What does the current skew level tell us about the next 30 days?

Volatility Smile vs Skew Across Asset Classes

The shape of the implied volatility curve varies by asset class, and each shape tells you what that market fears most.

Equities show skew: steep on the put side, declining on the call side. The market fears crashes more than rallies, and institutional demand for downside protection drives the asymmetry. This has been the dominant pattern since 1987, and it persists across individual stocks, sector ETFs, and broad indices.

Currencies show a true smile. In FX markets, a sharp move in either direction creates winners and losers. A euro rally is a dollar decline, and hedgers exist on both sides. That two-sided demand for tail protection creates the symmetric U-shape that textbooks describe.

Commodities display mixed patterns depending on the specific market. Agricultural commodities and energy can show reverse skew, with the call side elevated above the put side. Why? Supply shocks drive prices higher, not lower. A drought or a pipeline disruption creates upside tail risk that buyers need to hedge, which inflates call-side IV relative to put-side IV.

VIX options show reverse skew for a different reason. The VIX tends to spike rather than collapse, so OTM calls on the VIX carry higher IV than OTM puts. A VIX of 40 is far more probable than a VIX of 5, and the options market prices that asymmetry directly.

The shape of the curve is diagnostic. It tells you which tail the market is paying to protect against, and that information feeds directly into strike selection and strategy design.

How Volatility Skew Changes Over Time

Skew isn't static. It compresses and expands with market conditions, and those shifts carry information about regime changes and risk appetite.

In calm markets with low realized volatility and steady trending, skew tends to flatten. The demand for crash protection softens because the market feels safe. Put premiums still exceed call premiums, but the gap narrows. This compression typically coincides with VIX readings in the low teens and realized volatility tracking close to implied.

In stressed markets, skew steepens dramatically. The 2020 COVID crash saw 25-delta put skew on SPY surge to levels that dwarfed the prior two years of readings. The same dynamic played out during the tariff-driven selloff in April 2025. When fear arrives, skew is the first indicator to react, often before VIX fully reprices, because the bid for OTM puts accelerates faster than ATM IV adjusts.

The term structure of skew adds another dimension. Near-term skew (7 to 30 DTE) is typically steeper than longer-term skew (60 to 90 DTE) because near-term options are more sensitive to the immediate risk of a gap move. When near-term skew steepens relative to longer-term skew, the market is pricing a specific catalyst: an earnings announcement, an FOMC decision, or a geopolitical event. That steepening is a warning sign for premium sellers operating at short tenors.

Monitoring these shifts helps time premium selling decisions. A flattening skew in a calm market suggests reduced edge on the put side. A steepening skew in a nervous market suggests elevated premium that may compensate for the risk, or may signal an incoming dislocation that overwhelms the collected premium. For a deeper look at how these dynamics play out across the full volatility surface, the term structure of skew is where the most actionable signals live.

The ATM Put-Call IV Gap

Even at the money, where puts and calls share the same strike, implied volatility isn't equal. SPY's ATM put shows IV of 25.1% while the ATM call at the same strike reads 19.9%, a 5.2 percentage point gap.

This gap doesn't violate put-call parity. Put-call parity is a relationship between prices, not implied volatilities, and it holds perfectly well when put and call IVs differ. The gap exists because the market embeds directional risk into the volatility surface itself. ATM puts are more sensitive to the scenarios where skew matters most (a sharp decline), so the market prices them with higher IV even at the same strike.

Think of the ATM gap as the baseline from which skew radiates outward. It's the starting point, the minimum asymmetry between puts and calls. Every further move away from ATM amplifies that baseline into the steepening gradient we see at 25-delta, 10-delta, and 5-delta levels. The 5.2-point ATM gap becomes a 27.1-point gap at 5-delta. Skew begins at the money and accelerates from there.

Frequently Asked Questions

What is the difference between a volatility smile and volatility skew? A volatility smile is a symmetric U-shaped curve where both OTM puts and OTM calls carry higher implied volatility than ATM options. Volatility skew is an asymmetric pattern where OTM puts carry much higher IV than ATM options, while OTM call IV stays flat or declines. Equity markets have shown skew rather than a smile since the 1987 crash, because institutional demand for downside protection permanently inflated put-side IV.

Why do OTM puts have higher implied volatility than OTM calls? Two forces drive the asymmetry. On the demand side, pension funds and portfolio managers systematically buy OTM puts as crash protection, which inflates their price and implied volatility. On the supply side, market makers who sell those puts charge a higher premium to compensate for jump risk, the possibility that the market gaps through their hedges overnight. The 1987 crash, the 2008 financial crisis, and the 2020 COVID selloff all reinforced the lesson that left-tail risk is real and expensive to absorb.

Do all asset classes show the same volatility skew pattern? No. Equities show steep put-side skew. Currencies tend to show a true smile with symmetric wings, because hedgers exist on both sides of any currency pair. Some commodities show reverse skew with elevated call-side IV, reflecting supply-shock risk that drives prices higher. VIX options also show reverse skew, because the VIX is more likely to spike than collapse. The shape of the curve tells you which tail each market fears most.

How does volatility skew affect options pricing? Skew inflates the price of OTM puts relative to what a flat-volatility model would predict. A 10-delta SPY put carries 34.8% IV versus 14.5% for the same-delta call, meaning the put is priced for roughly 2.4 times the expected move of the call at the same probability level. For premium sellers, this means the put side of any short volatility structure generates a disproportionate share of the credit. For premium buyers, it means downside protection is structurally expensive.

Can we profit from volatility skew? The variance risk premium, the tendency for implied volatility to exceed realized volatility, concentrates on the put side of the skew. Selling OTM puts at elevated IV and capturing the spread between what options price and what the market delivers is the core of premium selling. But profiting from skew requires measuring the VRP to confirm that the elevated IV actually represents overpricing rather than a correct assessment of near-term risk. If you want to learn how to trade volatility using these signals, the VRP framework is the starting point.

What caused the shift from smile to skew in equity markets? The crash of October 19, 1987, when the S&P 500 fell 20.5% in a single session. Before that date, equity options showed a pattern closer to a symmetric smile. After, the market permanently embedded a fear premium into OTM puts. Rubinstein (1994) documented this structural shift using implied binomial trees extracted from post-crash option prices². Nearly four decades later, the skew persists because the institutional demand for crash protection has never subsided.

Conclusion

The volatility smile is a textbook diagram. Volatility skew is what you see when you pull up a live equity options chain. The distinction matters because skew tells you where overpricing concentrates by strike, and that concentration is the map for anyone selling premium or buying protection.

Every SPY option chain carries the memory of October 1987 in its shape. OTM puts are expensive because the market pays a structural premium for crash protection, and that premium is the spatial distribution of the variance risk premium across strikes. Measure it, track it over time, and let it guide your strike selection.

For more on how theta decay translates VRP into daily P&L, and why theta is the consequence of correctly identifying overpriced volatility rather than the edge itself, that's where the real framework begins.

Want to see live implied volatility by strike and delta for 400+ tickers? Sharpe Two provides real-time IV surfaces, VRP signals, and probability forecasts across the full options universe. Sign up for early access.

1. Black, F. (1976). "The Pricing of Commodity Contracts." Journal of Financial Economics, 3(1-2), 167-179. ↩
2. Rubinstein, M. (1994). "Implied Binomial Trees." Journal of Finance, 49(3), 771-818. ↩↩
3. Bates, D. (2000). "Post-'87 Crash Fears in the S&P 500 Futures Options Market." Journal of Econometrics, 94(1-2), 181-238. ↩