IV rank calculator
IV rank is where today's implied volatility sits between its 52-week low and high, as a percentage. An IV of 28% in a range of 19% to 62% gives a rank of 21%, which says the premium on that name is cheap by its own recent standards no matter how high 28% sounds.
The formula
(IV today - 52-week low) / (52-week high - 52-week low). Two data points define the scale, which is both why it is easy to compute and why it is fragile.
One volatility spike eleven months ago sets the high, and every reading since is measured against an event that no longer has anything to do with the stock. When the spike rolls off the window, the rank jumps overnight with no change in the option market at all.
IV rank against IV percentile
IV percentile asks a different question: what share of the last 252 trading days closed with a lower IV than today? It uses every observation instead of two, so it does not care about a single outlier.
They disagree in a specific and predictable way. A stock that sat at 20% IV for eleven months and spiked to 62% once will show a low IV rank and a high IV percentile at 28%. Rank says cheap. Percentile says this is elevated for how this stock normally trades. Percentile is right more often, and rank is quoted more often because it takes two numbers and a subtraction.
What to do with the number
Above 50 is the half of the range premium sellers want. Below 30 you are taking the same assignment risk for the smallest premium the name has offered in a year, which is a bad exchange even when the trade works out.
And rank only compares a stock against itself. A 60% rank on KO and a 60% rank on a clinical-stage biotech are not the same trade, are not the same risk, and should not get the same position size. Rank tells you whether the premium is good for this name. It tells you nothing about whether you want to be short this name.
Questions people actually ask
What is a good IV rank for selling options?
Most premium sellers want 50 or above, and many will not open a new position below 30. It is a preference, not a rule, and it matters less than whether the underlying is something you would be content to own or to sell.
Why is IV rank different on every platform?
Different IV series. Some use a 30-day constant-maturity IV, some use the front-month at-the-money contract, some use a proprietary blend. Same formula, different input, different answer. Compare ranks within one platform, never across two.
Can IV rank be above 100 or below 0?
Only if today set a new 52-week extreme, in which case the range has already moved and the correct rank is 100 or 0. This calculator clamps to that range.