Volatility smile: Answer Guide 2027
The volatility smile (or smirk/skew) is the pattern where implied volatility varies by strike price — typically higher for far out-of-the-money puts than for at-the-money options — contradicting the constant-volatility assumption of Black-Scholes. In a volatility smile interview question, describe the shape, explain the economics behind it, and note the 1987 origin.
Volatility Smile Interview Questions: What They Test
The shape first: plot implied vol against strike and you get a "smile" in some markets (FX) or a downward "smirk" in equities — OTM puts commanding much higher IV than OTM calls. The textbook model says the curve should be flat; the market disagrees, and the market is right.
The economics: crash fear. After the 1987 crash, investors permanently bid up downside protection, embedding fat-tail expectations into put prices. Portfolio insurance demand, leverage constraints, and the simple fact that markets fall faster than they rise all sustain the skew. Practitioners handle it with local-vol or stochastic-vol models rather than pretending Black-Scholes' flat vol is real.
How to Answer a Volatility Smile Interview Question
- Describe the shape. "IV plotted against strike is not flat — in equities it slopes down: OTM puts trade at much higher implied vol."
- Explain the economics. "Crash protection demand — investors pay up for downside puts because markets crash faster than they rally."
- Cite the history. "The skew steepened permanently after 1987 — the market learned tails are fatter than lognormal."
- Name the modeling fix. "Practitioners use local-vol or stochastic-vol models that take the smile as an input, not an error."
Common Mistakes in Volatility Smile Interview Answers
- Saying Black-Scholes is "wrong." It is a quoting convention now — traders quote in vol precisely because the smile exists.
- Forgetting the asymmetry. The equity skew is directional (downside bid) — a symmetric smile story misses the point.
- Ignoring the demand driver. It is not a math artifact — real hedging demand for puts sustains the pattern.
The smile is where textbook models meet market reality — shape, crash economics, and the 1987 break is the full answer.
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FAQ
Q: What causes the volatility smile? A: Market pricing of fat tails and crash risk — especially persistent demand for downside put protection since the 1987 crash.
Q: What is the difference between smile and skew? A: "Smile" describes a U-shape (common in FX); "skew" or "smirk" describes the downward slope typical in equity index options.
Q: Does the volatility smile violate Black-Scholes? A: It violates the constant-volatility assumption — which is why traders use Black-Scholes as a quoting language and handle vol variation separately.
Q: How do traders model the smile? A: With local volatility or stochastic volatility models calibrated to reproduce the observed smile across strikes and expiries.
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