Implied volatility (IV) tells you how much movement the options market is pricing in - but a raw IV number is useless without context. IV rank and IV percentile both answer the real question: is volatility high or low compared to its own recent history?

IV rank

IV rank places today's IV between its lowest and highest readings over a lookback period (usually a year). If IV ranged from 10% to 50% and sits at 30% today, IV rank is 50 - exactly halfway. It answers: where is IV within its range?

IV percentile

IV percentile instead asks: what fraction of days over the past year had a lower IV than today? An IV percentile of 80 means IV was lower on 80% of days - genuinely elevated. Percentile is often the more robust of the two because a single extreme spike can distort IV rank, while percentile reflects how often the level actually occurs.

"IV is 30%" tells you nothing. "IV is in the 85th percentile" tells you options are expensive right now.

Why it matters

These metrics shape whether buying options is a good deal today. High IV means richer premiums (and more risk of a volatility crush against you); low IV means cheaper options but potentially a sleepy tape. Knowing the volatility regime you are trading into is as important as your directional read - and it is the difference between overpaying and getting a fair price.