What is IV percentile?
In one line: IV percentile is the share of trading days in the past year on which a stock's implied volatility was lower than it is today, so a reading of 80 means today's IV is higher than on 80% of those days.
How it works
Implied volatility on its own is hard to judge. Is 35% high? For a utility stock, very. For a chip stock, maybe low. IV percentile answers that by comparing today's IV with the same stock's own past year.
It counts the days. If IV was lower than today on 200 of the last 252 trading days, the IV percentile is about 80. Today's IV is higher than usual for this stock.
IV rank does a similar job in a different way. It places today's IV between the year's lowest and highest readings. If the low was 20% and the high was 60%, an IV of 30% gives a rank of 25.
The difference matters after a spike. One crazy week with IV at 90% stretches the range, so IV rank looks low for months afterward even when IV is above normal. IV percentile counts days, so a single spike barely moves it. Many sellers in the wheel strategy prefer percentile for that reason.
An example (hypothetical)
An illustration, not a trade idea. Made-up stock XYZ trades at $50. Over the past year its IV ranged from 20% to 90%, but the 90% lasted only a few days after a sudden drop. Today IV is 38%.
- IV rank: (38 − 20) ÷ (90 − 20) ≈ 26. Looks low.
- IV percentile: IV was below 38% on about 180 of 252 days ≈ 71. Looks high.
You sell the 30-day $45 Put option for $1.00 because premium is richer than usual.
| What the month brings | XYZ at expiry | IV at expiry | Short put result |
|---|---|---|---|
| Nothing happens, IV drifts down | $50 | 28% | +$100 |
| Stock drifts lower, IV steady | $46 | 38% | +$100 |
| The reason for the high IV arrives | $40 | 55% | Assigned at $45: +$100 − $500 = −$400 |
The percentile was right that premium was rich. It couldn't say why. The last row is the why.
Why it matters for sellers
IV percentile is a quick filter. It won't pick trades for you, but it tells you whether you're selling premium that's high or low for this stock.
- High percentile: more premium, and more room for IV to fall, which helps a short option. Also a sign something may be expected. Check the earnings date.
- Low percentile: thin premium, and more room for IV to rise against you. See Vega risk.
A sensible habit: use both numbers. If rank and percentile disagree, as in the example, something unusual happened in the past year. Find out what.
Questions
What is the difference between IV rank and IV percentile?
IV rank places today's IV between the year's low and high. IV percentile counts how many days in the year IV was below today. Percentile is less distorted by one short spike.
What IV percentile is good for selling options?
Many sellers look for readings above 50, so IV is higher than usual for that stock. There's no magic cutoff. High readings often come with a known event, which is its own risk.
Does a high IV percentile mean the stock will fall?
No. It means the options market expects bigger moves than usual, in either direction. The premium is bigger because the risk is bigger.
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