IV Rank: range-based measurement
IV Rank = (Current IV − 52-week Low IV) / (52-week High IV − 52-week Low IV) × 100. It tells you where current IV sits within its annual high-low range. IV Rank 80 means current IV is 80% of the way between the lowest and highest IV seen in the past year. A single extreme spike can compress the scale — if IV spiked to 100% six months ago but normally trades 20-30%, even 35% IV will show a low IV Rank.
IV Percentile: time-based measurement
IV Percentile counts what percentage of trading days in the past year had IV lower than today. IV Percentile 80 means IV was lower than today on 80% of trading days. It is less sensitive to one-time spikes because it weights every day equally. A stock that briefly hit extreme IV will not compress the percentile scale the way it compresses IV Rank.
When the two metrics diverge
The biggest divergence happens after a volatility spike. If a stock had IV surge to 80% during a crisis but normally trades 20-30%, IV Rank will stay depressed for months (because 30% is still near the low end of the 20-80% range). IV Percentile recovers faster because it counts days, not range. Conversely, when IV slowly drifts higher without a spike, IV Percentile rises faster than IV Rank.
Which one to use for premium selling
Most premium sellers prefer IV Rank because the range-based approach directly answers: "How expensive are options right now compared to recent history?" When IV Rank is above 50, you are selling options priced above the midpoint of the annual range — the premium is rich. VolRadar uses IV Rank as the primary metric for the Scanner and Strategy Builder because it better identifies actionable premium selling opportunities.
Practical example
AAPL 52-week IV range: Low 18%, High 42%, Current 28%. IV Rank = (28 − 18) / (42 − 18) × 100 = 41.7 — below mid-range. IV Percentile might show 55 if IV was below 28% on 55% of days. Both suggest premium is not yet elevated, but IV Rank anchors to the actual range while IV Percentile reflects how frequently IV was lower. For strike selection, IV Rank above 50 signals a richer-than-average premium selling environment.
Limitations of both metrics
Both metrics use a backward-looking window (typically 252 trading days). Neither predicts future IV — they only contextualize the present. IV Rank is distorted by outlier spikes. IV Percentile can overstate richness during gradually rising IV trends. Smart premium sellers use IV Rank as the primary filter, then check VRP (IV minus realized volatility) to confirm that options are actually overpriced relative to how much the stock is moving.