One spike on 30 Mar 2026 sets the top of the rank scale for the months that follow
Both measures ask the same question: is today's IV high or low against its own history? Both need a long run of trading days, ideally a year, and one consistent series. Use the constant 30 day at the money series for Nifty, not the nearest weekly, because the weekly reading jumps around expiry.
Rank is a position in a range. It is today's IV less the lowest reading, divided by the highest less the lowest, times one hundred. The weakness is the range itself. One extreme day sets its top or bottom, and every other day is measured against that one day.
Percentile is a count. It is the share of past days on which IV was below today's reading. It does not care how extreme the highest day was, so a single spike cannot compress the rest of the year.
The chart shows the constant 30 day at the money IV of Nifty across the window. The high of 30 Mar 2026 sets the top of the rank scale for the months after it. On 10 Jun 2026 the rank sits in the lower part of that scale, while the percentile sits well above it, because most past days were lower than that day's reading. Same day, same series, two very different readings. The series here starts on 1 Jul 2025, so the window is about eleven months, not a full year.
Neither measure says the option is cheap or dear against the movement that follows. That is the question of realised against implied volatility. A low rank or percentile says only that the reading is unusual against the trailing year. The IV rank and percentile tool runs both on a dated series, so you can see the two numbers part ways after a spike.
Before you trade. Derivatives trading carries a high risk of loss. SEBI's study "Profitability of Individual Traders in the Equity Derivatives Segment (FY25 to FY26)" (August 2026) found that 87.7% of individual traders in equity F&O made net losses in FY26, with aggregate net losses of Rs 91,685 crore. Read the SEBI study