Implied volatility

Implied volatility, abbreviated IV, is the market’s forecast of how much an underlying will move in future, backed out of an option ’s traded premium using an option-pricing model, and expressed as an annualised percentage. It is called implied because it is not measured from price history but inferred from what traders are paying for the option today: given the premium, strike, time to expiry, spot and interest rate, IV is the volatility figure that makes the model’s price equal the market price. It is the single most important driver of an option’s time value after moneyness and time.

IV is forward-looking by construction, which separates it from historical volatility, the backward-looking measure of how much the underlying actually moved. Because IV is implied by demand for options, it rises when traders expect or fear a large move and falls when they expect calm, often independently of where price itself is going. A raw IV number carries little meaning on its own; it is read against its own history through IV rank and IV percentile.

This article defines IV and contrasts it with historical volatility, sets out IV rank and IV percentile, explains IV crush after events and the vega mechanism that makes IV move premiums, and shows where Kite surfaces IV. For the index-level version of expected volatility, see India VIX .

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How implied volatility is derived

An option’s premium can be split into intrinsic value and time value. The pricing model, Black-Scholes-Merton for European-style index options, takes the spot, strike, time to expiry, interest rate and a volatility input and returns a theoretical premium. Four of those inputs are observable. Volatility is not, so the model is run in reverse: the IV is the volatility figure that, fed into the model, reproduces the option’s actual traded premium.

Because IV is solved from the market price, it is a statement about what the option is worth to buyers and sellers right now, not a forecast anyone has written down. When demand for protection rises, premiums rise, and the IV solved from those richer premiums rises with them. This is why IV can climb while the underlying is flat: the market is paying up for the possibility of a move, not for a move that has happened.

Stock options on the National Stock Exchange are American-style, so the European Black-Scholes-Merton IV for them is an approximation, while index options such as the Nifty are European-style and the model fits cleanly. Kite displays the resulting per-strike IV in the option chain .

Implied volatility versus historical volatility

The two volatilities answer different questions, and the gap between them is itself a signal.

Historical volatility, also called realised volatility, is computed from the underlying’s past price moves, usually as the annualised standard deviation of returns over a trailing window. It is entirely backward-looking: it tells you how much the underlying did move, not how much it will. Implied volatility, by contrast, is the volatility the market is pricing into current premiums, so it is forward-looking.

The relationship between them sets whether options look cheap or dear. When IV is above HV, options are relatively expensive: the market is pricing in more future movement than the recent past delivered. When IV is below HV, options are relatively cheap by the same logic. Across many scheduled events, IV has tended to sit above the volatility that actually realised, which is the structural edge that disciplined option writers try to harvest by selling richly priced premium and managing the risk, though it is an edge in aggregate and not on any single trade.

IV rank and IV percentile

A raw IV of, say, 22 per cent means nothing until it is placed against the underlying’s own IV history. Two normalisations do that, and they can disagree.

IV rank measures where current IV sits within its 12-month high-low range. The formula is current IV minus the 52-week low, divided by the 52-week high minus the 52-week low, times 100. An IV rank of 80 means current IV is near the top of its yearly range; an IV rank of 10 means it is near the bottom.

IV percentile measures the share of days over the past year on which IV was lower than today. An IV percentile of 80 means IV was lower than today on 80 per cent of trading days in the past year, so today’s reading is genuinely elevated relative to most of the year.

The two diverge because IV rank is sensitive to a single extreme. If IV spiked once during the year, the 52-week high jumps, and IV rank can read moderate even when IV has actually been elevated on most days. IV percentile, which counts days rather than range position, smooths that one-off spike out. Many traders lean on IV percentile for that reason, and use both as a cross-check.

The standard strategy mapping follows from these. A high IV rank or percentile means options are richly priced, which favours selling premium, where falling IV helps a short-vega position. A low IV rank or percentile means options are cheap, which favours buying premium, where rising IV helps a long-vega position.

IV crush after events

IV crush is the rapid collapse in implied volatility immediately after a scheduled event resolves, most often a results announcement, removing the uncertainty premium that had been built into option prices.

The mechanism is straightforward. Before a known binary event, option buyers bid premiums up to cover the chance of a large surprise, and that extra cost is the event-volatility premium, which shows up as elevated IV. Once the event passes and the uncertainty is gone, options reprice lower almost instantly, and IV drops sharply. For front-month large-cap equity options, IV commonly falls 30 to 60 per cent after results: a stock carrying 80 per cent IV into the event might settle back to 30 to 35 per cent the next morning, even after a 5 to 10 per cent price move.

The crush is uneven across expiries. Front-month options carry the most event premium and are hit hardest; longer-dated options, 60 to 90 days out, carry less event-specific premium and fall less, so the term-structure kink flattens after the event. This unevenness is why a near-expiry long straddle into results can lose even when the move is large: the front-month vega exposure that gets crushed is exactly where the position sat.

Elevated IV does not guarantee a crush. IV can stay high or expand if uncertainty persists, for example after a guidance withdrawal or a macro shock, and sometimes IV is high for a good reason, so selling it blindly because it looks rich can mean selling fairly priced risk. Read IV crush as a high-probability tendency around clean, scheduled binary events, not a certainty.

The vega link

Vega is the bridge between implied volatility and the option’s price. Vega measures the change in an option’s premium for a one-point change in implied volatility, so it is the mechanism through which any IV move, including an IV crush, actually hits the position.

At-the-money options have the highest vega, so they gain value quickly when IV rises and lose value quickly when IV falls. When IV crush hits, vega works against the long-option holder: the position is long vega, IV drops, and the premium falls in proportion to the vega times the IV change. This is why being directionally right is often not enough into an event. A worked example: a Rs 100 stock with a Rs 8 at-the-money straddle prices in an 8 per cent move; if the stock moves 5 per cent but IV collapses from 80 to 32 per cent, the straddle might be worth Rs 4 to Rs 5 the next day, so the directional buyer was right and still lost, because the volatility contraction destroyed more value through vega than the directional move created through delta. For the full vega definition and sign conventions, see vega of options and how to read option Greeks on Kite .

Where Kite shows implied volatility

Kite surfaces IV per strike in the option chain , and in the Greeks view alongside delta , gamma , theta and vega for each call and put. Sensibull , integrated with Kite, adds IV charts and IV-rank style context that make the rank-and-percentile reading above easier to apply at a glance. For the index-level expected volatility of the Nifty, India VIX is the standard reference, computed by NSE from the Nifty option order book rather than from a single strike. Read per-strike IV for individual positions and India VIX for the broad volatility regime.

See also

• Vega of options
• India VIX
• Option premium
• Delta of options
• Gamma of options
• Theta and time decay
• Open interest
• Change in open interest
• Put-call ratio
• Max pain theory
• ITM, ATM and OTM moneyness
• Strike selection for options
• Black-Scholes model
• How to use the options chain on Kite
• How to read option Greeks on Kite
• Futures and options
• Nifty 50
• Bank Nifty
• National Stock Exchange
• Expiry-day options trading
• Weekly versus monthly expiry
• Zerodha F&O segment
• Kite by Zerodha
• Zerodha Varsity
• Sensibull
• Volatility indicators overview

External references

• Zerodha Varsity: Options theory and Greeks module
• NSE: Option chain
• NSE: India VIX index
• CBOE: Volatility education
• SEBI: Investor education on derivatives

References

1. Zerodha Varsity, Options Theory module, on implied volatility, the Greeks and Black-Scholes-Merton pricing (accessed June 2026).
2. National Stock Exchange of India, option chain per-strike implied volatility data.
3. IV rank formula: current IV minus 52-week low, divided by 52-week high minus 52-week low, times 100 (standard market definition).
4. Observed post-event IV behaviour: front-month large-cap equity IV commonly falls 30 to 60 per cent after a scheduled results announcement (options-market practitioner data).