Volatility Term Structure in Options Explained Simply
Volatility term structure is the curve you get when you plot implied volatility for the same underlying across different expiries. Normally it slopes upward, because a far month option carries more uncertainty than a near month one. When it inverts, the market is pricing a known event in the near term.
Traders read this curve the way bond traders read the yield curve. Its shape carries information a single volatility number cannot.
What the Normal Shape Looks Like
Take an illustrative Nifty snapshot with spot at 24,000. At the money implied volatility might read like this:
| Expiry | Days to expiry | At the money IV |
|---|---|---|
| Current week | 3 | 11.0% |
| Next week | 10 | 12.2% |
| Current month | 24 | 13.1% |
| Next month | 52 | 13.8% |
| Three month | 80 | 14.4% |
This upward slope is called a normal or contango term structure. Two forces create it. More calendar time means more chance of a shock, and long dated options are harder to hedge, so market makers ask for wider volatility.
Why the Curve Inverts
Inversion means near dated implied volatility sits above far dated. It happens when a specific dated event falls inside the near expiry but not the far one, so the near option must price a jump the far option spreads over more days.
Common Indian triggers:
- Quarterly results for a single stock, where the reporting date is known weeks ahead.
- RBI Monetary Policy Committee outcomes, which move Bank Nifty and rate sensitive stocks.
- Union Budget day, historically one of the sharpest single session moves for Indian indices.
- Election results and major state poll counts.
- Sharp selloffs, where panic bids up front month protection faster than long dated protection.
An inverted curve is not a forecast of direction. It only says the market expects the near term to be bumpier than the medium term.
A Single Stock Illustration
A stock trades at Rs 1,450 and reports results in four days. Weekly at the money implied volatility prints 46% while the two month reading sits at 28%. The near contract has to compress one uncertain event into very few days, so the annualised figure balloons. After results are out, that 46% typically collapses toward the 28% area within a session.
How Weekly Expiries Distort the Near End
India has an unusual options market. Weekly index expiries mean the shortest contract can have one or two trading days left, and at that horizon the implied volatility number becomes unstable.
Three specific distortions to watch:
- Annualisation noise. Implied volatility is quoted per year. Dividing a one day expectation by the square root of a tiny time fraction magnifies small premium changes into large volatility swings.
- Pin risk and cheap tails. On expiry day, out of the money options trade at Rs 1 or Rs 2 with a tick size of Rs 0.05, so the quoted implied volatility jumps around for reasons that have nothing to do with real expectations.
- Weekend and holiday gaps. Most models count calendar days, so a Thursday expiry followed by a long weekend gives a different reading from a plain midweek expiry.
The practical fix is to ignore the very front contract when judging the curve’s shape, or compare weekly to weekly and monthly to monthly rather than mixing them.
Reading the Curve Before an Event
Here is a workflow that does not need any software beyond a live option chain.
- Note at the money implied volatility for the expiry before the event and the expiry after it.
- Measure the spread. A wide spread means the event is already priced generously in the near contract.
- Check whether the event date actually falls inside the near expiry. Traders lose money by buying the wrong expiry and holding an option that expires before the news lands.
- Compare today’s spread with what it looked like ahead of the previous two or three similar events for that underlying.
The common misconception is that a high near term implied volatility means an option is overpriced. It may simply be correctly priced for a real event. What matters is whether the eventual move exceeds what the premium was charging, and nobody knows that in advance.
Frequently Asked Questions
Is India VIX the same as the term structure?
No. India VIX is a single number derived from near month Nifty option prices, roughly a 30 day volatility expectation. The term structure is the whole set of readings across expiries, so India VIX is one point on that curve.
Which expiry does a calendar spread depend on?
A calendar spread is a direct trade on the shape of the curve, since you sell one expiry and buy another on the same strike. Its profit depends on how the spread between the two implied volatilities changes, not just on where spot goes.
Why does my broker show different IV for the same strike?
Implied volatility is back solved from the traded premium, so a stale last traded price or a wide bid ask spread gives a distorted figure. Use the mid price of the bid and ask for a cleaner reading.
Does the curve invert during a market crash?
Usually yes. Demand for immediate protection spikes, so front month implied volatility rises faster than the back months and the curve flips downward sloping until conditions settle.
Key Takeaways
- Term structure plots implied volatility across expiries for the same underlying.
- An upward slope is normal because more time means more uncertainty.
- Inversion signals a dated event inside the near expiry, such as results, an RBI policy meeting or the Budget.
- Weekly Indian expiries make the front end noisy, so compare like expiries.
- High near term implied volatility is not proof an option is mispriced.
