TWO NUMBERS CAN LOOK AT THE SAME STOCK ON THE SAME DAY AND TELL YOU COMPLETELY OPPOSITE THINGS!!! One says the premium is average. The other says it's the highest it's been in a year. Both are correct. Here's which one to actually trust: They're called IV Rank and IV Percentile, and most people don't know there's a difference. Quick bit of context first. Implied volatility on its own tells you nothing. 40% IV is enormous on Coca-Cola and completely normal on a biotech. You need to know if it's high for that specific stock. IV Rank puts today's reading between the lowest and highest of the last year. Current minus the low, divided by the range. If IV ran 20 to 60 and it's 40 today, that's a rank of 50. IV Percentile is the share of days in the last year where IV closed lower than today. Now the example that shows why this matters. Say IV sat between 20 and 25 for basically the whole year. Then one day it spiked to 60 on some news. Today it's at 40. Rank says 50. Looks average, nothing special. Percentile says 98. IV has been below today's level on 98% of trading days. Rank got destroyed by one outlier because it only looks at two extremes. Percentile counts every single day, so it tells you what's actually normal for that name. How I use them. Percentile decides whether I sell. Above 50 you're getting paid more than usual. Above 70 is genuinely good. Under 30 and you're taking real risk for almost nothing. Rank is still handy for spotting a stock that just moved. A sudden jump means something happened recently. Two things worth knowing. Both default to a one year lookback. After a calm year the baseline resets underneath you and high IV starts reading as normal. And high IV is high for a reason. Earnings, litigation, a merger. A great percentile reading isn't a green light, it's a prompt to go find out why.