ATM IV
Every strike has its own implied volatility, but the market’s one-number verdict on how much the index will move is the IV at the money. Everything else is skew around it.
In short: ATM IV is the implied volatility of the option strike closest to the current underlying price, usually read as the average of the ATM call and put IVs for a given expiry. Because the at-the-money option has the most time value and the highest vega, its IV is the cleanest measure of the volatility the market is pricing, and it is the reference point from which the skew of other strikes is measured. Divided by the square root of the number of trading periods, it gives the expected move: at 14% annualised, NIFTY at 24,000 is priced for about 212 points a day.
The intuition
An option’s price has two parts, intrinsic and time value, and implied volatility is backed out of the time value. The at-the-money strike has no intrinsic value and the largest time value of any strike, so its price is almost pure volatility and its IV is the least noisy. Far strikes carry small premiums where a tick of mispricing moves the IV a lot, and they also carry the demand premium of hedgers, which is the skew. The ATM IV strips that out and answers the simple question: how much movement is this expiry pricing?
Formula
ATM IV = average of the implied volatilities of the ATM call and the ATM put for the same expiry (or the IV interpolated to the forward price)
Expected one-day move ≈ S × ATM IV × √(1 ÷ 252)
Expected move to expiry ≈ S × ATM IV × √(T), with T in years, or approximately 0.8 × the ATM straddle price
Worked example (illustrative prices)
Suppose NIFTY is at 24,000 and the monthly 24,000 call and put, 30 days to expiry, trade at ₹451 and ₹323 with an IV of 14% each.
| Measure | Calculation | Result |
|---|---|---|
| ATM straddle | 451 + 323 | ₹774 |
| Expected move to expiry (straddle shortcut) | 0.8 × 774 | about 620 points, or 2.6% |
| Expected move to expiry (formula) | 24,000 × 0.14 × √(30/365) | about 963 points as one standard deviation; the straddle shortcut gives the expected absolute move, which is smaller |
| Expected one-day move | 24,000 × 0.14 ÷ √252 | about 212 points |
| Vega of the ATM call | price change per 1 vol point | about ₹27 per unit, so a rise to 15% adds about ₹1,760 per lot |
If the chain’s 30-day realized volatility is 8.4%, the Vol Spread between implied and realized is 5.6 points: the market is pricing much more movement than it has recently seen. If India VIX is at 13 on the same day, the 30-day ATM IV at 14 is close to it, which is expected since VIX is built from near-the-money NIFTY options across the next two expiries.
Why it matters
- It sets the price of time. Theta on every strike scales with ATM IV; a chain at 14% decays faster in rupees than one at 10%.
- It is the reference for rich or cheap. IV rank and percentile are computed on ATM IV, and the term structure is the ATM IV of each expiry plotted against time.
- It defines the expected range. Strategy selection, strike selection for strangles and condors, and the width of a protective hedge all begin from the expected move that ATM IV implies.
- It moves on events. ATM IV rises into results, budgets and policy days and collapses afterwards; the collapse is IV crush, and it hits ATM options hardest because they have the most vega.
Common mistakes
- Reading a single strike’s IV as the market’s view. A far out-of-the-money put at 19% is skew; the market’s volatility forecast is the ATM figure.
- Treating one standard deviation as the expected move. The formula gives a one-sigma range, which the index stays inside about two thirds of the time; the straddle shortcut gives the smaller expected absolute move.
- Comparing ATM IVs across expiries without adjusting for time. A 7-day ATM IV of 16% and a 30-day ATM IV of 14% describe different horizons; the forward volatility between them is what the longer contract adds.
- Forgetting that the ATM strike moves. When the index moves 100 points the ATM strike changes, and the quoted ATM IV switches to a different option whose IV already included some skew.
Indian specifics
With NIFTY strikes 50 points apart, the ATM strike is always within 25 points of spot, so NSE’s chain gives a clean ATM reading without interpolation; on BANKNIFTY the 100-point step means the nearest strike can be 50 points away. India VIX, published by NSE, is computed from the bid-ask midpoints of out-of-the-money NIFTY options in the two nearest expiries and interpolated to 30 days, so it tracks the 30-day ATM IV closely but is not identical to it. Weekly Tuesday expiries mean the nearest-expiry ATM IV on NSE is often a 1-to-7-day figure and swings sharply on expiry day; the monthly ATM IV is the stabler benchmark.
FAQ
What is ATM IV?
The implied volatility of the at-the-money strike (average of ATM call and put IV), the chain's benchmark for priced movement.
How do I convert ATM IV into an expected daily move?
Spot × IV ÷ √252. At 24,000 and 14%: about 212 points a day.
Is ATM IV the same as India VIX?
Not exactly; VIX is a 30-day figure built from OTM NIFTY options, so it tracks the 30-day ATM IV closely but not shorter expiries.
Why is ATM IV lower than the IV of far strikes?
Skew. OTM puts and far calls carry demand premiums; the ATM strike is the low point of the smile.
How does the ATM straddle relate to ATM IV?
Straddle ≈ 0.8 × spot × IV × √T; the ATM straddle price is a quote of the expected move to expiry.
ATM IV, IV Rank and Vol Spread on one strip
The TradePulse option chain’s analytics strip shows ATM IV, IV Rank and the Vol Spread between IV and 30-day historical volatility, with the ATM IV coloured when elevated.
Related terms
- Implied volatility, the measure itself
- IV rank, ATM IV against its own history
- Volatility skew, how other strikes differ from ATM
- Straddle, the market’s expected-move quote
- India VIX, NSE’s 30-day volatility index
- Term structure, ATM IV across expiries