VIX primer and volatility forecasting

The VIX is not a simple fear gauge. It is Cboe’s estimate of the S&P 500’s expected volatility over the next 30 days, derived from option prices. (cboe.com) A new YouTube lecture from Susquehanna features Doug Costa, a former math professor and former head of quantitative research there, explaining how the index is built from S&P 500 options rather than from stock moves alone. The video was available on YouTube by April 17, 2026. (youtube.com) Cboe’s methodology uses out-of-the-money S&P 500 puts and calls with expirations bracketing 30 days, then interpolates those prices into a constant 30-day measure. The official rule set uses options with more than 23 days and less than 37 days to expiration. (cdn.cboe.com) That makes the VIX an implied-volatility measure, which means it reflects what option prices say traders expect. Realized volatility is different: it measures how much the S&P 500 actually moved over a past window. (rpc.cfainstitute.org) The distinction matters in forecasting tests because implied volatility is forward-looking and realized volatility is backward-looking. A model that predicts future swings should be compared with later realized moves, not with the VIX itself unless the target is option-implied expectations. (rpc.cfainstitute.org) The same caution applies to trading products tied to volatility. Spot VIX is an index calculation, while VIX futures are separate contracts with their own prices and expirations. (cboe.com) On April 16, 2026, Cboe’s term-structure page showed spot VIX at 17.79 for May futures, 19.74 for June, and 20.76 for July, with later contracts higher still. That upward slope is contango, a market shape that often appears when near-term stress is lower than longer-dated expected volatility. (cboe.com) When the curve flips and near contracts trade above later ones, the market calls it backwardation. Traders often read that as a sign that a volatility shock is already in the market rather than merely being priced for later. (cboe.com) The VIX also changed over time. Cboe introduced the original index in 1993 using S&P 100 options, then rebuilt it in 2003 around S&P 500 options and a broader, model-free variance approach developed with Goldman Sachs. (cdn.cboe.com) Costa’s lecture lands in a market where “VIX” is often used as shorthand for panic, even though the number is a 30-day options estimate and not a direct reading of today’s fear. For anyone testing forecasts or trading volatility products, that definition is the starting point. (youtube.com)