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IV Rank vs IV Percentile: Definitions and Why They Disagree

IV rank vs IV percentile: formulas, why one spike makes them disagree, 126- and 252-session windows, minimum history, and what a "good" IV rank is.

Reviewed · Sources at the end · How Vyreon measures
Vyreon's per-security reports are not live yet; this page describes what they will measure. Examples are illustrative.

IV rank and IV percentile both describe whether today's implied volatility is high or low compared with the same security's own past. IV percentile is the share of past sessions with lower IV. IV rank is where today sits between the lowest and highest IV of the period. They can disagree, and the disagreement is informative.

IV Percentile

IV percentile counts how many past sessions had lower implied volatility than today:

IV percentile = (sessions with IV below today's) ÷ (usable sessions in the window)

An IV percentile of 80% means today's IV is higher than on 80% of the sessions in the window. It uses every observation, so a single unusual day cannot move it much.

IV Rank

IV rank places today on the scale between the period's low and high:

IV rank = (today − lowest) ÷ (highest − lowest)

An IV rank of 0% means today is the lowest of the period, and 100% means it is the highest. Because it depends only on the two extremes, one spike can compress every other reading toward zero for months.

Why IV Rank And IV Percentile Disagree

Illustrative example: over the window a security's IV mostly ranged from 15% to 18%, with a brief spike to 40%. Today's IV is 20%.

  • IV percentile is high, perhaps 90%, because today is above nearly every session.
  • IV rank is (20 − 15) ÷ (40 − 15) = 20%, because the spike stretched the range.

Neither is wrong. The percentile says that today is high compared with typical days, and the rank says that today is far below the recent extreme. A rank of 50% does not mean half the sessions were lower.

What Is A Good IV Rank?

There is no universal threshold. Rules of thumb such as "above 50" are trading conventions, not measured thresholds. What counts as high depends on the security, the window and what happened inside it. Vyreon reports the numbers with their windows and does not label any level good or bad.

How Vyreon Measures It

  • Input: Vyreon's own 30-day at-the-money implied volatility (IV30), the same method on every day. See implied volatility.
  • Windows: the previous 126 trading sessions (about six months) and the previous 252 (about a year).
  • Percentile: today is compared with the earlier sessions only. Ties do not count as below.
  • Rank: the low and high include today, so a new high reads exactly 100% and a new low 0%. If every value is equal, rank is withheld.
  • Minimum history: at least 63 usable sessions for the 126-session window and 126 for the 252-session window. With less, the context is withheld, but today's IV30 is still shown.
  • Older sessions are never substituted to fill gaps in the window.

What It Does Not Tell You

  • A high reading means options are expensive relative to this security's own past. It does not mean IV will fall.
  • It is not a probability. "Higher than 80% of sessions" does not mean an 80% chance of anything.
  • It cannot be compared across securities as a measure of absolute cost. A low-percentile growth stock can still carry far higher IV than a high-percentile bond ETF.

Related: implied volatility · IV vs realized volatility · IV term structure · earnings expected move and IV crush

Sources

  • John C. Hull, Options, Futures, and Other Derivatives (Pearson, many editions): implied volatility.
  • Fischer Black and Myron Scholes, "The Pricing of Options and Corporate Liabilities", Journal of Political Economy (1973): the model from which implied volatility is solved.

IV rank and IV percentile are practitioner conventions with no single originator; we know of no peer-reviewed source that defines them.