What this calculator solves
IV rank helps normalize a ticker's current implied volatility against its own history. A 45% IV can be high for one stock and low for another, so the range matters.
Formula
IV rank = (current IV - lookback low IV) / (lookback high IV - lookback low IV) x 100. Values near 0 mean current IV is near the low end of the range. Values near 100 mean it is near the high end.
Example
If current IV is 42%, the 1-year low is 20%, and the 1-year high is 70%, IV rank is (42 - 20) / (70 - 20) x 100 = 44%.
Risk reminder
IV rank does not say an option is cheap or expensive by itself. Earnings, skew, liquidity, realized volatility, and market regime can all change the interpretation.