VIX vs Realised Volatility Spread Trades

VIX is often described as "the market's fear gauge," but mechanically it is a specific number: the implied volatility, backed out from S&P 500 option prices, of a hypothetical 30-day option. It tells you what the options market is pricing volatility to be over the next month. It is not, and never claims to be, a forecast of what volatility will actually turn out to be — that number, computed after the fact from how much the index actually moved, is realised volatility.

VIX has historically averaged higher than the realised volatility that follows it, a gap known as the variance risk premium. VIX-versus-realised spread trades are strategies built directly around harvesting that gap — essentially, systematically selling insurance against volatility because the price of that insurance tends to run a bit rich.

How the spread is captured

The most direct route is a short variance swap or short VIX futures position, both of which profit if realised volatility comes in below what was implied when the position was opened. A simpler retail-accessible version sells short-dated index straddles or strangles repeatedly, systematically betting that the premium collected (priced off implied volatility) exceeds the eventual cost of the hedging or losses driven by how much the index actually moved.

Worked example

VIX is at 18 (implying an expected 18% annualized volatility over the next 30 days). A trader sells a delta-neutral straddle priced off that 18% implied volatility. Over the following month, the index actually realizes 13% annualized volatility — a calmer month than the options market had priced in.

Because realised volatility came in below implied, the straddle seller profits: the option premium collected, calibrated to 18% vol, was more than enough to cover the hedging costs generated by the index's actual 13%-vol path. Roughly, the seller's gain scales with the difference between implied and realised variance (volatility squared), so even a moderate gap between 18% and 13% translates to a more-than-proportional edge, because variance, not volatility itself, is what a delta-hedged short-vol position is actually short.

Now suppose instead the index has a sharp two-day sell-off mid-month that pushes realised volatility for the month up to 30%, well above the 18% implied at entry. The same trader now loses money, and the loss similarly scales more than proportionally with the gap, because it is squared in variance terms — a small miss in realised volatility can produce an outsized gain or loss relative to what the raw volatility numbers alone would suggest.

What this means in practice

The variance risk premium exists, historically, because most market participants are net buyers of volatility protection — pension funds, insurers, and levered investors all want downside insurance, and someone has to be paid to sell it to them. That is also exactly why the premium isn't free money: sellers are being compensated for bearing a risk (sharp volatility spikes, usually coinciding with sharp price drops) that buyers are paying to avoid, and the spread trade's return distribution is asymmetric — small, steady gains most months, and occasional sharp losses when realised volatility spikes.