Introductory Context
"For practical options trading, understanding the volatility surface reduces to understanding two cross-sections of this surface: the volatility skew (the variation of implied volatility across different strike prices for the same expiry) and the volatility term structure (the variation of implied volatility across different expiry dates for the same strike). These two dimensions explain why the 23,000 PE has a different implied volatility than the 24,000 CE (even though they are equidistant from ATM), and why the current-month ATM option has a different implied volatility than the next-month ATM option at the same strike. "
The Volatility Skew - Different IV for Different Strikes
For equity options -- both global and Indian -- the volatility skew follows a consistent pattern: OTM put options have higher implied volatility than equivalent OTM call options. For Nifty options: an OTM put at 22,500 (when Nifty is at 23,500 = Rs 1,000 below ATM) might have implied volatility of 18.5 percent. An OTM call at 24,500 (Rs 1,000 above ATM, equidistant in the other direction) might have implied volatility of 14.2 percent. The 18.5 versus 14.2 percent difference -- 4.3 percentage points -- is the volatility skew for this specific pair.
The skew's direction (puts more expensive than equidistant calls) is persistent across equity markets globally and is particularly pronounced in Indian index options. It exists because: (1) Portfolio managers and institutions systematically buy OTM puts for downside protection, creating persistent excess demand for OTM puts that inflates their IV premium. (2) Market crashes tend to be faster and larger than market rallies -- the left tail of equity return distributions is fatter than the right tail, and options prices reflect this through higher put IV. (3) Local factors in India: large FII selling episodes (sudden reversal of foreign capital) have historically created sharp Nifty declines that add to the put skew premium.
The Term Structure - Different IV for Different Expiries
The volatility term structure describes how implied volatility changes across expiry dates for the same strike. The normal term structure (contango): near-term IV is lower than longer-term IV. The near-term options are calm (the market's immediate uncertainty is low) while the longer-dated options carry higher IV (more uncertainty over a longer period). This is the typical structure in stable, non-event markets.
The inverted term structure (backwardation): near-term IV is higher than longer-term IV. This occurs immediately before major scheduled events (Budget, elections) when near-term options carry the event's IV premium while longer-dated options (which are post-event) price in a return to normalcy. It also occurs during market crises when immediate fear is priced at its maximum in the nearest-dated options. The term structure inversion before events is the analytical foundation for calendar spreads (Topic 16.8): selling the high-IV near-term option and buying the lower-IV longer-term option captures this inversion as income when the near-term option expires (and its high IV collapses) while the longer-term option retains its moderate IV.
Nifty Volatility Surface Cross-Sections
Skew (across strikes, same expiry): 22,000 PE IV: 20.5%. 22,500 PE IV: 18.8%. 23,000 PE IV: 17.2%. 23,500 ATM (both CE and PE): 15.5%. 24,000 CE IV: 14.1%. 24,500 CE IV: 13.2%. Pattern: IV falls as strikes move from deep OTM puts toward ATM, then falls further as strikes move toward OTM calls. Term structure (across expiries, same ATM strike): Weekly (5 sessions): 12.8%. Monthly (20 sessions): 15.5%. Next month (45 sessions): 16.2%. 3-month (65 sessions): 16.8%. Normal contango: near-term lower than longer-term.
The Volatility Smile vs Volatility Smirk
In equity markets (including India), the volatility surface's strike-cross-section produces a 'volatility smirk' rather than the theoretical 'volatility smile'. A volatility smile (from early Black-Scholes theory) would show IV highest at ATM and declining symmetrically toward both OTM calls and OTM puts. In practice, equity options show the smirk: IV is highest for deep OTM puts, declines through ATM, and continues declining (more slowly) for OTM calls. The smirk is the visual representation of the put skew -- the left side of the smile is elevated while the right side is suppressed.
The smirk has specific practical implications for Indian options traders: (1) Selling OTM puts (collecting the elevated put IV) provides more premium per unit of OTM distance than selling equivalent OTM calls -- because put IV is higher. This is why the bull put spread's short put generates more income than the bear call spread's short call at equivalent delta levels. (2) Buying OTM puts as portfolio insurance is more expensive than the equivalent OTM call -- the put skew premium is the 'insurance premium' built into downside protection. (3) The iron condor's put wing naturally generates more credit than the call wing at equivalent delta levels -- reflecting the structural put skew.
Reading the Surface in Sensibull
Sensibull's Options Trader platform provides direct visual access to the Nifty volatility surface through two displays. First: the IV column in the option chain view shows the implied volatility for each individual strike -- reading down this column reveals the skew profile for the current expiry. Second: the 'Volatility Analysis' feature (available in the Sensibull Pro plan) shows the IV across multiple expiries for the same strike, revealing the term structure. Before entering any calendar spread, diagonal spread, or complex volatility position, read both these displays to understand: (a) which expiry has unusually elevated IV (suggesting event pricing) and (b) which strikes have elevated IV relative to their neighbours (suggesting concentrated demand or specific event risk at that level).
The volatility surface is the options market's complete revelation of what participants believe about the distribution of future prices. Every point on the surface -- every combination of strike and expiry -- tells a specific story about the market's fear and expectation. The put skew tells the story of institutional hedging demand. The term structure tells the story of event timing and post-event normalisation. Reading these stories is what separates the volatility-aware options trader from the directional trader who uses options merely as leveraged directional instruments.
Using ATM IV as the Only Volatility Reference Is a Major Analytical Error
Many traders refer to 'India VIX' or 'options IV' as if every option has the same implied volatility. The volatility surface makes clear why this is wrong: a 22,000 PE might have IV of 21% while a 24,000 CE has IV of 13% -- both for the same expiry. Using 'VIX 15.5' as the reference for both options significantly misestimates the premiums of OTM puts (they are priced above VIX-implied levels) and OTM calls (priced below VIX-implied levels). Always check the specific IV of the option being traded from the option chain, not just the index-level VIX.