The essentials in 30 seconds
- Cboe calculates the VIX from selected S&P 500 put and call quotes.
- Its target horizon is about 30 days; the published number is annualised.
- VIX 20 is a 20% annualised volatility measure, not a forecast of a 20% loss.
- It is a market-implied measure; volatility realised later can differ.
- “Fear index” is a useful nickname but an incomplete definition.
What the fear index means in plain language
Options prices change when market participants place a higher value on protection against large moves. The Cboe Volatility Index, or VIX, uses selected options quotes to summarise that priced-in volatility.
The underlying index is the S&P 500, a US share index. The VIX is therefore not a measure for every individual share, the DAX or a particular ETF portfolio.
Implied volatility is inferred from option prices. Realised volatility describes moves that actually occurred. What prices imply today and what happens later are different quantities.
Where the VIX number comes from
Cboe does not use one popular option. Its method selects S&P 500 puts and calls across strikes and uses bid-ask midquotes. A strike is an option’s agreed exercise price; different strikes cover different possible index levels.
Under the published methodology, eligible expirations are more than 23 and less than 37 days before the relevant Friday expiration. Information from two suitable expirations is weighted to a constant 30-day horizon. Strike filters, quote rules and weightings make the calculation more than an average of displayed option IVs.
See what a higher VIX changes
This simplified example scales an annualised volatility measure to 30 days. The illustrated range widens in both directions as VIX rises; it does not automatically move downward.
Change a hypothetical VIX value. Starting index: 5,000 points. The illustrative range opens in both directions.
Lower model value
4,713
Starting point
5,000
Upper model value
5,287
Approximate 30-day move: ±5.73 %
Wider range ≠ predicted direction
Teaching model: (VIX ÷ 100) × √(30 ÷ 365). Constant volatility, simple time scaling, no drift. This is neither a dependable probability distribution nor a fixed price boundary. Moves outside the range are possible. No live data.
Why 30 days can be shown as an annual figure
Annualised means expressed on a one-year scale so figures can be compared. VIX 20 is therefore a 20% annualised volatility quantity derived from prices related to the coming 30 days.
Hypothetical VIX 20 · 30 calendar days
A simple time scaling gives 20% × √(30/365) ≈ 5.73%. At an assumed index level of 5,000, that corresponds to about 287 points on either side, or roughly 4,713 to 5,287.
This teaching range is not a boundary the index must stay within, and it assigns no particular crash probability.
The calculation assumes constant volatility and square-root-of-time scaling. Real volatility and risk premiums change; prices can jump. One VIX reading does not establish a dependable distribution of all possible outcomes.
Why “fear index” tells only part of the story
When uncertainty rises or shares fall, demand for protection often increases, which can lift options prices and the VIX. That makes the nickname understandable, but the index measures quotes, not emotions.
Those quotes reflect both expectations and the price of bearing volatility risk. A high VIX can coexist with a rising market. It can also fall after bad news if the news resolves uncertainty.
What the VIX cannot tell you
It gives no exact timing or price target. It concerns the S&P 500 rather than one company. It also cannot, by itself, tell whether a particular option is cheap or expensive.
The VIX is an index, not an asset you can buy directly. VIX futures, options and related products have their own prices, expirations and settlement rules; they may move differently from the spot VIX.
For a specific option, you also need its underlying, strike, remaining time and relevant volatility. Our guide to the parts of an option price explains how they fit together.
Further detail: show assumptions and context
The VIX method aggregates option prices into an annualised 30-day variance quantity, then publishes its square root multiplied by 100. Strikes, time weights, the forward index level and interest-rate assumptions enter the calculation.
“Expected volatility” here is a risk-neutral quantity implied by option prices, not an unbiased statistical forecast under real-world probabilities. Risk premiums and the shape of option prices matter.
Our illustration uses 365 calendar days, matching the methodology’s calendar-time convention. Its symmetric range omits drift, skew, jumps and changing volatility, and we deliberately assign it no fixed probability.
What to learn next
Reading VIX levels, the DAX counterpart and tradable VIX products.
Separate an individual option’s IV from this index measure.
See price, time and volatility together.
Explore the model effect of changing volatility.
Glossary
- Implied volatility
- A volatility quantity inferred from option prices.
- Annualised
- Expressed on a one-year scale for comparison.
- Realised volatility
- A measure of price movements actually observed in the past.
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