The VIX Index measures the 30-day expected volatility of the U.S. stock market. The calculation for the index is derived based on the call and put options prices of the S&P 500 index.
In layman’s terms, the VIX index can be seen as a way to gauge the general market sentiments and the level of fear among the overall market participants. This is why the VIX index is also commonly being referred to as the fear index.
To understand how the VIX index works, we need to first understand the impact of psychology of the market participants on the stock market itself. When market participants are fearful about the uncertainties and the outlook of the stock market, there tends to be more selling pressure. They are fearful of holding on to the equities which also translates to lower demand for equities. Hence, this pushes down the stock market prices.
Since the VIX index gives us a gauge of the level of fear, we can see that the VIX index moves in the opposite direction as the S&P 500. When the market is getting fearful, prices of VIX increase while prices of the S&P 500 decline.