The implied volatility cheat sheet

What implied volatility is, exactly what moves it, how to tell whether a reading is high, and the five working rules that matter.

Quick answer: The IV cheat sheet states what implied volatility is — the volatility that makes a pricing model reproduce an option's market price — lists the seven events that move it and in which direction, shows why IV Rank and IV Percentile routinely disagree, and gives the five working rules that follow from implied volatility being a price rather than a forecast.

Implied volatility is the number in an option chain that nobody quotes and everybody trades. This page is everything about it that fits on one screen. The full treatment is in the implied volatility section.

What it is, exactly

Definition: Implied volatility is the volatility input that makes an option pricing model output the option's current market price. It is not observed and it is not forecast — it is solved for. Everything below follows from that.

How an implied volatility is actually extracted

Black–Scholes price of a 30-day 24,000 NIFTY call as the volatility input varies.

Price is monotone increasing in volatility, so exactly one volatility reproduces any quoted price. That number is the implied volatility.

What moves it

When this happens	IV does this	Because
Demand for options rises	IV rises	Somebody must be induced to sell. Price is how.
A scheduled event approaches	IV rises	The uncertain day sits inside the option's remaining life.
The event resolves	IV collapses overnight	The uncertainty it priced no longer exists. This is IV crush.
The underlying falls sharply	IV rises, a lot	Put demand plus a genuine rise in expected movement.
The underlying rises sharply	IV falls, a little	The asymmetry is the whole reason skew exists.
Time passes, nothing happens	IV drifts down	Realised movement undershoots what was priced.
Expiry approaches	The QUOTE becomes unreliable	Premium → 0, so σ is computed by dividing by nearly nothing.

Is 13% high?

Unanswerable without context, which is exactly what IV Rank and IV Percentile supply — and they disagree.

The same day, the same data, two different readings

One year of illustrative at-the-money NIFTY implied volatility.

IV Rank divides by a range that a single spike can define. IV Percentile counts every day equally. Because volatility has a long right tail, the percentile normally reads higher.

It is a surface, not a number

Every strike prints its own IV. The pattern across strikes is the smile or, on an index, the skew.
Every expiry prints its own IV. The pattern across expiries is the term structure.
Put the two together and you have the volatility surface. Quoting "the IV" of an underlying means quoting one point on it, almost always the near-month at-the-money.

The volatility surface

Strike runs left–right, time to expiry front–back, implied volatility is height.

Black–Scholes assumes this surface is a flat plane. The market has never once agreed.

Working rules

IV is a price, not a forecast. It is a biased forecast — it usually exceeds subsequent realised volatility, which is the volatility risk premium — and it is worst exactly when it matters most.
Compare like with like. A 30-day IV against a 30-day realised volatility. Never a 30-day IV against a 10-day HV.
An OTM option's entire value is volatility. It has no intrinsic value. Buying one is a volatility trade wearing directional clothing.
Vega ∝ √T, gamma ∝ 1/√T. Long-dated options trade the level of IV; short-dated options trade movement. "Long volatility" without saying which is not a statement.
Ignore the IV of a nearly-expired option. It is a division by almost zero.

The mistake that costs the most money. Selling options because implied volatility is "high" assumes high IV means overpriced. It usually means the market is about to move more, and it moves more precisely when the position is largest. High IV is not an edge. The gap between IV and subsequent realised volatility is — and it is small, positive on average, and occasionally catastrophically negative.

Frequently asked questions

What is implied volatility in one sentence?

Implied volatility is the volatility input that makes an option pricing model output the option's current market price. It is solved for, not observed and not forecast.

Does high IV mean the stock will move a lot?

It means the option market is charging as though it will. On average implied volatility slightly exceeds the movement that arrives, which is the volatility risk premium, but the exceptions are enormous and arrive when positions are largest.

Why does IV collapse after earnings or a policy announcement?

Because the uncertainty the option was charging for no longer exists once the outcome is public. This is IV crush, and it is the option correctly ceasing to price a risk that has resolved — not a market inefficiency.

What is the difference between IV Rank and IV Percentile?

IV Rank measures position within the 52-week range and is set by just two days. IV Percentile counts what share of all days closed below today. Because volatility has a long right tail, the percentile usually reads higher, and the gap tells you a spike is distorting the rank.

Why does every strike have a different implied volatility?

Because real returns have fat tails and, on an equity index, a fatter left tail. Out-of-the-money puts therefore command more than a constant-volatility model says they should. Plotted across strikes, that pattern is the smile or the skew.

Can I ignore the implied volatility of an option about to expire?

You should. The at-the-money premium collapses toward zero with the square root of remaining time, so the solver is dividing by nearly nothing and a single tick implies an enormous change in volatility.

Last reviewed 10 July 2026. Educational content only — not investment advice.