Options numbers
IV Rank, explained
Implied volatility tells you how much movement option prices assume. IV Rank tells you whether that is high or low for this particular stock. How both work, and what they can’t tell you.
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First, implied volatility
Implied volatility (IV) is the amount of movement that option prices assume for a stock, written as a yearly percentage. It isn’t measured from past prices; it is worked backwards from what options cost today. When traders expect bigger moves, they pay more for options, and IV goes up.
IV is useful, but on its own it is hard to judge. An IV of 35% might be unusually high for a steady utility and unusually low for a young biotech company. To know whether options are expensive for a particular stock, you need to compare today’s IV with that stock’s own history. That is what IV Rank does.
What IV Rank measures
IV Rank places today’s IV on a scale from 0 to 100, where 0 is the lowest IV of the past 52 weeks and 100 is the highest.
Formula
IV Rank
IV Rank = (today’s IV − 52-week low) ÷ (52-week high − 52-week low) × 100
Example
Working it out
Suppose a stock’s IV ranged from 20% to 60% over the past year and is 35% today. Its IV Rank is (35 − 20) ÷ (60 − 20) × 100 = 37.5, or about 38: a little below the middle of its range.
Readings near 0 mean options on this stock are about as cheap as they have been all year; readings near 100 mean they are about as expensive. A reading of 50 means today’s IV sits halfway between the two extremes, which isn’t the same as typical: if IV spent most of the year near its low, a rank of 50 is unusually high for this stock.
IV Rank vs IV Percentile
IV Percentile asks a different question: on what share of trading days in the past year was IV lower than it is today?
Example
Same stock, different number
If IV was below 35% on 180 of the last 252 trading days, the IV Percentile is 180 ÷ 252 = 71. The stock’s IV Rank is about 38, but its IV is higher than on most days of the year.
Now suppose the 52-week high was a single-day spike to 90%. IV Rank becomes (35 − 20) ÷ (90 − 20) × 100 = 21, while IV Percentile stays at 71, because one unusual day barely changes a count of days.
Neither is better in every case. IV Rank is simple and shows where IV sits in its range; IV Percentile is harder to distort with one extreme day. Looking at both gives a fuller picture.
Why it matters for option prices
IV is one of the main inputs to an option’s price. Holding everything else equal, higher IV means a higher price for both calls and puts.
| Implied volatility | Call price per share | Per contract |
|---|---|---|
| 20% | $2.45 | $245 |
| 35% | $4.16 | $416 |
| 60% | $7.01 | $701 |
Every point of IV is worth about $0.11 a share on this option (that is its vega), or about $11 per contract. That is why a change in IV can move an option’s price even when the stock stands still.
For someone buying options, a high IV Rank means paying more than usual for this stock, and the option can lose value if IV falls back. For someone selling options, it means collecting more than usual, in exchange for the market expecting bigger moves. Neither side gets something for nothing.
IV and the expected move
IV can be turned into a rough range for the stock. Over a short period, the one-standard-deviation move is about price × IV × √(days ÷ 365). Under the model’s assumptions, the stock finishes inside that range roughly 68% of the time.
Example
A 30-day range
For a $100 stock with IV of 35%: $100 × 0.35 × √(30 ÷ 365) ≈ $10.03. Options are pricing a range of roughly $90 to $110 over the next 30 days, with about a one-in-three chance of a move beyond it, in either direction.
What IV Rank can’t tell you
Risk
High IV usually has a reason
IV often rises ahead of earnings, a court ruling, a drug trial result or a market sell-off. A high IV Rank may simply mean the market correctly expects a big move. “Expensive” options can still turn out to be cheap if the move is larger than expected.
- It is relative to one year. A stock that was calm all year can show a high IV Rank at an IV that would be normal for most stocks.
- It doesn’t predict direction. IV says how much the stock might move, not which way.
- IV can stay high or keep rising. A high reading is not a promise that it will fall back soon.
- Different expirations have different IVs. Make sure you know which IV a rank is based on; many sources use options about 30 days out.
How to use it alongside other numbers
IV Rank works best as context. Before acting on it, check what is coming up (especially the next earnings date), how far the expected move reaches, and how liquid the options are, since wide bid-ask spreads can cost more than any edge from timing IV.
It also helps to watch IV Rank over time rather than as a single reading. A rank that has climbed for weeks ahead of a known event tells a different story from one that jumped overnight on unexpected news, and a rank that stays high after the event has passed may be telling you the market sees lasting uncertainty.
For how IV feeds into the odds of a trade, read Probability of profit (POP), explained. For what happens to IV around results, see How earnings move stocks.