Volatility Smile

OTM options have higher IV than ATM options. Creates smile shape when plotted.

Volatility Skew

Puts typically have higher IV than calls. Reflects demand for downside protection.

Implications

  • OTM puts expensive (insurance)
  • OTM calls cheaper (speculation)
  • ATM options best value

Trading Application

Understanding skew helps in strike selection and strategy construction.

The Anatomy of the Volatility Smile

The volatility smile is the U-shaped curve formed when you plot implied volatility against strike prices for options with the same expiration. After the 1987 crash, deep OTM puts started trading far above the Black-Scholes fair value, and deep OTM calls followed suit, bending the flat theoretical line into a smile. In the Indian market the curve is rarely a perfect U; it is usually a smirk, with the left wing rising more sharply because downside protection is always in demand.

Why the Smile Exists

  • Fat tails: Markets move violently more often than a lognormal model suggests, so tail options must be priced higher.
  • Supply and demand: Institutional hedging concentrates buying pressure in OTM puts, lifting their premiums.
  • Crashes are feared: Skew persists because investors pay a premium to sleep at night during uncertainty.

Reading the Skew in Nifty and Bank Nifty

Compare the implied volatility of the 5% OTM put against the 5% OTM call. When the gap widens sharply, protection buyers are panicking and a washout may be near; when the gap narrows, the market is complacent. A 92:100 ratio on the 95-105 skew is normal; anything beyond 1.15:1 signals genuine fear.

How Traders Exploit the Skew

  1. Skew sellers: Sell the expensive OTM puts and buy the cheap OTM calls, pocketing the premium difference as theta works.
  2. Risk reversal: Buy the put and sell the call to own the skew on a zero-cost structure.
  3. Vertical spreads: Buy the skew-rich option and sell a further OTM leg to finance the risk.

Practical Checks Before Trading the Smile

Always measure the skew on the same expiration and after adjusting for the risk-free rate; otherwise the numbers are not comparable. Notice when the smile flattens during calm sessions, because that is when strangle sellers on short expiry face their biggest risk: a sudden re-pricing of tail risk. Finally, remember that the smile is an input, not a signal; use it to choose which option is priced fairly, then stack your directional bias on top.

Smile by Expiry Tenure

The smile is not a fixed sculpture; it changes with time to expiry, and intraday traders should read the pattern per tenure:

  • Short-dated expiries show a pronounced smile because pin-risk and event risk make tails expensive near zero DTE.
  • Mid-tenure (30-90 DTE) smiles flatten; the term structure shows the smile is a horizon-dependent risk premium, not a static quote.
  • Long-dated tenures smirk less because compounding uncertainty smooths out one-off gap risk.

Reading tenure matters for choosing which expiry to trade: the smile shape is your first filter between weekly structures and monthly structures.

Skew as an Insurance Price

The skew (higher IV on OTM puts than OTM calls) is best understood as the cost of crash insurance, and it moves with fear:

  • When Bank Nifty puts price 6-8 IV points richer than calls, the market has already bought crash protection; sellers of that protection are collecting event insurance premium.
  • Steepening skew before an event is rational, cheapening after is normalisation; a flat skew into a known catalyst is the anomaly to distrust.
  • Skew trades (selling the skew by owning puts and selling the equal calls) harvest this premium but carry the left-tail risk they are literally selling.

Reading Indian Index Skews

India's skew has a fingerprint worth learning:

  • Nifty typically skews softer than Bank Nifty because the index diversifies idiosyncratic bank stress.
  • Around policy months the put side of Bank Nifty steepens visibly, while Nifty's call side catches up after rallies (a "smirk"), the tell of a market that sells rump upside aggressively.
  • Expiry-week skews are dominated by gamma and pin mechanics rather than crash insurance; do not read weeklies through the same lens as monthly tenors.

Arbitrage Limits: Why Smiles Don't DVL Close

Why does nobody trade the smile away? Because real money surfaces constrain the arbitrage:

  • Bid-ask widths near the smile's tails eat the theoretical profit; the edge inside a 2-point wide far-OTM quote rarely covers the fill.
  • Margin and capital destroy the neck-up; selling expensive puts requires an equal offsetting position, and the risk budget disappears before the math does.
  • Inventory funding: a market maker's smile mirror bears financing and hedging cost the public trader never prices.

A Model-Free Variance Reading

The professional way to consume the smile is never raw levels but the variance it implies:

  1. Collect all strikes' mid-prices at a single tenure and integrate across the chain; the result approximates the market's variance forecast, the model-free approach used by VIX-style indices.
  2. Compare that implied variance to the recently realised variance; the spread (variance risk premium) tells you whether options as a family are cheap or rich right now.
  3. Trade the family, not the strike: buy the variance when it trades below realised and above its own mean, sell it when the reverse.

The smile and its skew are the ledger of the market's fear and greed for the exact horizon you hold. Traders who price insurance, calibrate the variance risk premium and respect tenure grammar outperform traders who chase a "hidden edge" in the curve itself; the edge is earned by positioning around the premium, not by outsmarting its display.