What is the VIX?

The VIX, formally the CBOE Volatility Index, measures the stock market's expectation of 30-day forward-looking volatility. It is calculated from the prices of S&P 500 index options and represents the annualized expected percentage move in the S&P 500 over the next 30 days. A VIX reading of 20 implies the market expects approximately a 5.8% move (20 divided by the square root of 12) in the S&P 500 over the next month.

The VIX earned its "fear gauge" nickname because it tends to spike sharply during market selloffs and periods of uncertainty. When investors are worried about potential declines, they buy protective put options on the S&P 500, bidding up option premiums and pushing the VIX higher. During calm, uptrending markets, demand for protection falls and the VIX declines.

Historical context helps interpret VIX levels. A reading below 15 indicates complacency and low expected volatility, common during extended bull markets. Readings between 15 and 25 are considered normal. Above 25 indicates elevated fear. Above 35 signals significant market stress. The VIX reached its all-time high of 82.69 on March 16, 2020, during the COVID-19 crash, and hit 80.86 during the 2008 financial crisis.

Importantly, the VIX has a well-documented mean-reverting property. After spikes, it tends to decline relatively quickly, which is why volatility selling (through instruments like short VIX ETPs) has been a popular, if risky, strategy. The VIX also exhibits a negative correlation with the S&P 500: when stocks fall, VIX rises, and vice versa. This relationship is not perfectly symmetric, as VIX tends to spike faster on declines than it drops during rallies.

For portfolio management, the VIX provides actionable information. Extremely low VIX readings may signal complacency and vulnerability to a volatility shock. Very high readings historically offer attractive entry points for risk assets, as peak fear often coincides with market bottoms. The VIX is also the basis for a large ecosystem of tradable products, including futures, options, and ETFs, which allow investors to express views on future volatility directly.