VIX: how to read the stock market's fear gauge

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The VIX measures how much the options market expects the S&P 500 to fluctuate over the next 30 days, expressed as annualised volatility in percentage points. When fear rises, the price of protection rises, and with it the VIX. That is why it is also called the fear gauge. If you can read it, you understand a lot about sentiment, hedging costs and the pitfalls of volatility products.

What the VIX measures

The VIX is calculated from the prices of many options on the S&P 500, not from past prices. Under the methodology of Cboe (2019), options with more than 23 and fewer than 37 days to expiry are included, and the result is interpolated from two maturities to exactly 30 days. Puts and calls across many strike prices are used; this produces a model-free estimate of expected variance, without having to assume an option pricing model such as that of Black and Scholes (1973).

Behind the calculation lies an insight worked out by Carr and Wu (2009): the fair price of a variance swap (a contract that exchanges the variance that actually materialises for a fixed rate) can be replicated well with a portfolio of options. The VIX is the square root of this rate for 30 days, multiplied by 100. So it is a price for volatility, not a forecast in the statistical sense.

Converting the VIX into an expected move

The figure is a standard deviation. Under a normal distribution, around two thirds of moves would fall within this range. In reality, stock returns have fat tails: large swings occur more often than the bell curve suggests (see skewness and kurtosis).

Typical values

An analysis of daily closing values from January 1990 to October 2026 gives:

Closes above 50 only occurred in the 2008/09 financial crisis, in March and April 2020 and on a single day in April 2025 (52.33 on 8 April). On 5 August 2024, the VIX briefly shot up a long way during the trading session but closed at 38.57. The VIX rises quickly in crises and falls back slowly afterwards. Volatility models such as ARCH by Engle (1982) and GARCH by Bollerslev (1986) describe this pattern with clusters of volatile phases.

Term structure and contango

Besides the VIX, there are indices for 9 days, 3 months, 6 months and 1 year. In calm phases, the curve rises with maturity (contango): little fear is priced in for the short term, more uncertainty for the long term. In crises it inverts (backwardation). A common measure is the ratio VIX / VIX3M. A value above 1 signals stress.

Roll yield: why VIX ETPs lose over time

You cannot buy the VIX itself, only futures on it. In contango, the future is above the VIX and converges on it by expiry. If you are long, you lose continuously in the process.

Whaley (2013) examined the exchange-traded products on short-term VIX futures since their launch in 2009 and reached a clear verdict:

Volatility premium, VVIX and SKEW

• Volatility premium: the VIX minus the volatility that actually materialised (e.g. over the last 21 trading days). Usually positive: on average, protection costs more than it pays out. Example: VIX 19, realised 10 → premium of 9 points. Since 1990, the difference has averaged around 4 points and has been above zero on 88% of days.
• VVIX: the volatility of the VIX itself, derived from VIX options. Since 2006, it has been between 83 and 102 on half of all days, and between 76 and 115 on 80% of days.
• SKEW: the price of protection against severe market crashes, derived from far out-of-the-money options. The median since 1990 is 120; values above 141 occurred on only 10% of days.
• Correlation: when the S&P 500 falls, the VIX rises. Since 1990, the daily change in the VIX and the return of the S&P 500 have had a correlation of −0.79; over 63-day windows, the correlation was mostly between −0.89 and −0.57.

Carr and Wu (2009) show that the premium is positive for indices and individual stocks: implied variance is, on average, above realised variance. Bollerslev et al. (2009) also show that a high variance premium heralded higher stock returns in the following months, especially over a quarter. Whaley (2000) explains why the VIX works as a fear gauge: it measures the demand for protection, which rises sharply in downturns.

For advanced readers: variance, not volatility

• VIX² is the price of variance: the index is derived from expected variance under the risk-neutral measure. Because the square root is a concave function, the fair price of a volatility future is below the square root of the variance swap rate. The difference grows with uncertainty about volatility (measured by the VVIX).
• Not a pure expectation: because investors pay for protection, the VIX contains a risk premium. On average, it systematically overestimates future volatility.
• Mean reversion: volatility is persistent but returns to its long-term level. Futures with longer maturities are therefore below the VIX in crises and above it in calm times.
• Skew in option prices: far out-of-the-money puts are relatively expensive (volatility skew); the SKEW index translates this slope into a number.

How to use the VIX as an investor

1. Put the expected move into context: convert the VIX into a monthly range and compare it with what you are willing to tolerate in your portfolio. A VIX of 30 means that monthly moves of around 9% are perfectly normal right now.
2. Understand hedging costs: a high VIX makes puts expensive. If you only hedge once the crisis has started, you pay the highest price. Diversification across asset classes is usually cheaper than options.
3. The curve, not a single value: a rising VIX with a term structure that is still flat or upward-sloping is less alarming than an inverted curve with the VIX above the VIX3M.
4. Plan rather than react: a fixed rebalancing plan automatically takes advantage of high volatility because it buys more in downturns, without you having to time the VIX (see rebalancing).

Limitations and common mistakes

• Not a timing signal on its own: very high values have often coincided with good entry points, but only in hindsight; low values do not tell you when the next shock will come.
• US market only: for European equities there is the VSTOXX; it moves similarly but is often somewhat higher.
• Products, not the index: if you want to trade volatility, you trade futures or options with roll costs and contract risks. The performance of the VIX itself is no yardstick for that.
• Short volatility: strategies that sell protection earn steadily for a long time and lose rarely, but then heavily. The Sharpe ratio underestimates this risk (see Sharpe ratio).

How Portfolio Lab calculates it

The Volatility dashboard shows VIX9D to VIX1Y, VVIX and SKEW from the indices' daily closing values, and the curve of monthly VIX futures from settlement prices (contract data for the last three years). Realised volatility is the standard deviation of the daily log returns of the S&P 500 over 21 trading days × √252, and the premium is the VIX minus this figure. Contango is M2 / M1 − 1; M1 is the first contract with more than six days to expiry. The roll yield follows the formula above, and the correlation uses 63 trading days. Each metric appears with its percentile rank in the chosen period (1, 3 or 5 years or the full history). Details in the volatility dashboard methodology. Risk-neutral probabilities of declines of 10% and 20%, derived from the VIX, VIX 3 months and VIX 6 months, are shown in the Market expectations tab on Macro (see market expectations).

This article explains a method; it is not investment or tax advice. Worked examples are simplified and rounded. All terms in the glossary.