Is This IV High? Rank, Percentile and Skew
Drag a marker along a year of IV and watch rank and percentile disagree — sometimes badly.
Worth reading first: Implied Volatility Is a Price, Not a Prediction
Course contents73 lessons · 28 questions
The previous lesson ended on a question it could not answer: is 34% implied volatility high? Not without context. This lesson supplies two kinds of context — one across time, and one across strikes.
IV rank: where you sit in the year's range
IV rank = (current IV − 52-week low) ÷ (52-week high − 52-week low) × 100A simple position between two endpoints.
If a stock's implied volatility has ranged from 20% to 60% over the past year and sits at 30% today, its IV rank is 25. You are in the bottom quarter of the range — premium is cheap by this stock's own standards.
The weakness is visible in the formula: it depends entirely on two numbers, the high and the low. A single panic day a year ago can set a high that distorts every reading since.
IV percentile: how many days were lower
IV percentile = days in the past year with IV below today ÷ total days × 100A count, not a range.
Same stock, same day, different question. If 180 of the last 252 trading days had lower implied volatility than today, the IV percentile is 71 — today is higher than 71% of the year, regardless of where the extremes sat.
Because it counts days rather than measuring a span, one outlier barely moves it. That makes it more robust, and it is why many traders prefer it.
Where the two measures disagree
A year of daily implied volatility with one spike in it. Drag today's IV and watch rank and percentile give different answers about the same day.
52-week range: 20.6% to 62.3%
One spike in the year stretches the high, which drags IV rank down for every subsequent day — while IV percentile, which only counts days, barely notices. That is why the two figures can point in opposite directions on the same chain.
| Today's IV | IV rank | IV percentile | What it means |
|---|---|---|---|
| 22% | 11 | 18 | Both agree: cheap |
| 32% | 31 | 82 | Sharp disagreement |
| 45% | 53 | 95 | Rank understates it |
A stock that spent most of the year near 25% IV, with one spike to 70%.
The middle row is the one to sit with. IV rank says 31 — sounds unremarkable, maybe a bit cheap. IV percentile says 82 — today is more expensive than four days in five. Both are computed correctly from the same data. The spike stretched the range, which permanently depresses every subsequent rank reading, while the percentile just counts.
Skew: context across strikes
The second kind of context. A single stock does not have one implied volatility — it has one per strike, and they are not equal.
The volatility curve across strikes
Implied volatility plotted against strike price. Flatten the skew to zero to see the symmetric smile that textbook models assume, then raise it to see what equity chains actually look like.
0 = flat smile, 1 = steep put skew
Downside strikes carry more implied volatility than upside ones. Crashes are faster and more correlated than rallies, and demand for downside protection is persistent — so the market charges more for it. Flatten the skew to zero and the curve becomes the symmetric smile the textbook model assumes.
Downside puts consistently carry higher implied volatility than equidistant upside calls. That is skew, and on equities it is close to universal. Three reasons, all real:
- Crashes are faster than rallies. Markets fall harder than they rise, so large downside moves genuinely are more likely than the symmetric model assumes.
- Protection has persistent buyers. Funds hedge downside continuously. Steady demand raises the price.
- Correlation rises in selloffs. Everything falls together, which makes index downside particularly expensive.
The shape is called the volatility smile when it curves up on both sides, and a skew or smirk when — as on most equities — the put side is clearly higher.
What skew means if you sell puts
Something quietly good: you are selling the expensive side of the curve. A put seller is supplying exactly what the persistent hedging demand wants, and gets paid a premium above the at-the-money level for it.
And something worth knowing: skew is why a 0.20 delta put pays noticeably more than a 0.20 delta call on the same stock. If you have ever wondered why the put side of the chain looks more generous, this is the answer — and it is compensation for a genuinely fatter tail, not an inefficiency.
What can go wrong
Using IV rank alone after a volatility spike. It will read low for a year afterwards and tell you premium is cheap when it is not.
Selling only on high IV rank. High readings cluster around genuine trouble. Treat it as one input, not a trigger.
Expecting a flat volatility curve. Any model or tool that assumes one is systematically mispricing the wings.
Reading steep skew as an opportunity. It steepens most when the market is most worried, which is the moment the extra premium is most earned.
Key takeaways
- IV rank measures where today sits between the year's low and high; IV percentile counts how many days were lower.
- One spike distorts IV rank for a year afterwards, while IV percentile barely notices — prefer percentile, and watch when they disagree.
- Implied volatility differs by strike. Downside puts carry more than equidistant calls: that is skew.
- Skew exists because crashes are faster than rallies and protection has persistent buyers — it is compensation, not inefficiency.
- Put sellers are selling the expensive side of the curve, which is a real and structural advantage.
Check your understanding
1. A stock ranged 20%-60% IV this year and sits at 30% today. What is its IV rank?
2. IV rank reads 31 and IV percentile reads 82 on the same day. What does that tell you?
3. Why does a 0.20 delta put usually pay more than a 0.20 delta call on the same stock?