IV rank needs IV history; this curve uses HV
Implied volatility comes from option prices under a pricing model. Historical volatility measures observed changes in the underlying price. A current option-chain snapshot cannot reconstruct a year of historical IV. This page fetches closing prices, so its historical curve is HV range rank. The separate call IV card is a current available snapshot and never enters that curve.
To build a comparable IV-rank series, first define a consistent measure: for example, a fixed maturity and moneyness convention, with documented interpolation and observation times. Collect that same measure over the lookback. Ranking a different strike or expiry each day without controlling those choices can mix market changes with contract-selection changes.
Reproduce the historical calculation
- Sort the returned daily closes by date. For each consecutive pair, calculate r = ln(close today / close previous). Invalid dates, duplicate dates and nonpositive closes stop the calculation; they are not replaced with zero.
- For each window of 20 returns, subtract the sample mean, square the deviations, sum them and divide by 19. Take the square root, multiply by √252, then multiply by 100 to display annualized HV as a percentage.
- For each window of 252 HV observations, calculate 100 × (latest HV − minimum HV) / (maximum HV − minimum HV). The current observation is included. At least 272 valid closing-price observations are needed for the first rank.
- Trim the results to the chosen display period. The display period changes which dates are shown, not the 20-return HV window or the 252-observation rank window. The table lists the latest 30 displayed observations.
Hypothetically, HV of 25% within a 15%–35% range has a range rank of 50%. This means halfway between those endpoints; it does not mean that half the observations were below 25%. If every HV value in the window is equal, the denominator is zero and the rank is unavailable. The chart leaves a gap rather than inventing a midpoint.
Read the chart without turning a label into a trade
The 20 and 80 lines are visual thresholds. They do not measure the probability of a reversal and do not establish that options are cheap or expensive. A high HV rank can reflect a recent large realized move while option IV has already fallen, or while option IV has risen further. Selling premium based only on this chart ignores future events, skew, spreads, assignment and loss exposure.
A range rank is sensitive to the most extreme observations. It can change when an old high or low leaves the rolling window, even if current HV barely changes. A percentile instead counts the proportion of observations below the current value; the choice of whether ties count must be stated. Neither statistic establishes an expected trading return.
Inspect dates, coverage and adjustment conventions
The price input is the provider's historical EOD close field. This tool does not independently repair corporate actions or build a dividend-reinvestment series. Check the provider adjustment convention when a split or dividend affects a return. Missing sessions are not synthesized; a multi-session gap is still a consecutive-observation return, which can distort a daily annualization. The √252 convention assumes approximately 252 return observations per year.
The display request adds a 450-calendar-day warmup buffer, but new listings, missing records or provider limits can still shorten the visible history. Read the actual first and last dates and observation count. The displayed-period HV high and low are not automatically a 52-week range. Retrieval time is not the timestamp of a new market observation.
The optional call snapshot searches up to 250 returned contracts for a standard future-expiry call with a strike nearest the separate stock quote. It does not follow pagination or hold maturity constant. Its contract ID, strike and expiry are shown so the observation can be checked. Missing option data does not prevent calculation of the historical price-based chart.
Sources and related method
OIC distinguishes historical and implied volatility. Massive documents snapshot fields, pagination and plan-dependent data. The formulas and limitations above describe this page's implementation, reviewed October 21, 2026. For a manual range calculation using an independently verified IV history, see the IV rank calculator.