VIX and the term structure

The VIX is the most quoted number in markets after the indexes themselves, and one of the most misread. It is not a fear gauge in any mystical sense. It is a price: the price the options market is charging for protection over the next thirty days, expressed as an annualised volatility. Once you treat it as a price, its behaviour becomes much easier to use.

What the VIX measures

The VIX is computed from S&P 500 index options with roughly 23 to 37 days to expiry, weighted to represent a constant 30-day horizon. It is the market's implied expectation of annualised volatility for that window. A VIX of 16 means the options market is pricing an expected annualised standard deviation of about 16%.

The conversion that matters for a trader is to daily terms:

expected daily move ≈ VIX ÷ √252 ≈ VIX ÷ 15.9

which is why the "rule of 16" exists. VIX 16 implies about 1% expected daily moves; VIX 32 implies about 2%; VIX 80 (the 2008 and 2020 peaks) implies about 5%.

Two properties follow. The VIX is mean-reverting: it cannot stay at 45 for long because that requires the S&P to move 3% a day indefinitely, and it cannot stay at 10 for long because complacency eventually meets an event. And the VIX is inversely correlated with the S&P on most days, roughly -0.7 to -0.8, because declines raise demand for puts and rallies reduce it.

Implied vs realised

The VIX is a forecast. Realised volatility is what actually happened. Most of the time implied is above realised by a few points; that gap is the premium option sellers collect for bearing tail risk, and it is why simply "buying VIX" as a hedge is expensive over time.

When realised exceeds implied, the market is moving more than the options priced. That happens in crashes and at the start of trending declines, and it is the condition under which short-volatility strategies lose most.

For a trader the cleanest use is the ratio: VIX ÷ 20-day realised vol. Well above 1 means options are expensive relative to recent movement; near or below 1 means they are cheap and the market is moving more than expected. Neither is a directional signal; both say something about whether to buy or sell options in your own trades.

Key idea: The VIX is the price of 30-day S&P protection expressed as annualised volatility. Divide by 16 for the implied daily move. It is mean-reverting, inversely correlated with the index, and usually a few points above what is then realised.

The term structure

The VIX is one point on a curve. VIX futures trade for each of the next several months, and the CBOE also publishes shorter and longer-dated indexes (a 9-day version, a 3-month version, a 6-month version). Plotting them by expiry gives the term structure.

Contango (normal):                Backwardation (stress):

   vol                                vol
    │            ___──                 │ ╲
    │       __──                       │  ╲__
    │  __──                            │     ‾‾──___
    │─                                 │            ‾‾──
    └──────────────────── expiry       └──────────────────── expiry
     spot  1m  2m  3m  6m               spot  1m  2m  3m  6m

Contango: later expiries are priced higher than near ones. This is the normal state, present most of the time, because uncertainty grows with horizon and because far-dated options carry a bigger premium for unknown unknowns. Contango is consistent with a calm, rising market.

Backwardation: near expiries are priced higher than later ones. Traders are paying more for protection this month than for protection in six months, which only happens when the stress is now. Backwardation appears in corrections and crashes and usually resolves back to contango as the stress passes.

The simplest single measure is the ratio of the spot VIX to the 3-month index:

Using the structure

As a regime label. "VIX 14, contango" and "VIX 28, backwardation" are two different markets. The first supports pullback buying and breakout follow-through. The second supports fading extremes, smaller size and wider stops.

Flips as events. The moment the curve flips from contango to backwardation is a meaningful escalation and often comes a day or two after the first sharp drop. The flip back to contango, while the index is still well below its highs, has often marked the point where the worst of a correction is over. Neither flip is a trade on its own; both belong in the journal.

Extremes as contrarian context. Steep backwardation with VIX above 35 and the VIX/VIX3M ratio above 1.15 has frequently appeared within days of a tradeable low. It has also persisted for weeks in 2008 and briefly in 2020. It says "capitulation is happening", not "capitulation is over".

What the VIX does not do

• It does not predict direction. It prices magnitude.
• It does not "have to" fall because it is high. It usually does, on a timescale of weeks, but the index can fall a further 20% while the VIX drifts from 45 to 35.
• It is not a breadth measure. A narrow rally with a 12 VIX is calm on the surface and fragile underneath. Pair it with Module 3.
• Low VIX is not a sell signal. Long stretches of the strongest bull markets have run with the VIX between 10 and 14.

Try it: For the last two years, mark every day the VIX/VIX3M ratio crossed above 1.0 and every day it crossed back below. Note the index's position on each date and the return over the following 20 sessions. Then check: did the flips back to contango cluster after lows? How often did a flip into backwardation see the index lower a month later? Two columns of numbers beat any narrative about "fear".

Recap

• The VIX is the implied 30-day volatility of the S&P 500 from index options; VIX ÷ 16 is the implied daily move.
• It is mean-reverting, inversely correlated with the index, and usually above the volatility then realised.
• The term structure is the curve of VIX indexes and futures by expiry; contango is normal, backwardation means stress is now.
• VIX ÷ VIX3M above 1.0 flags backwardation; flips in either direction are regime events worth logging.
• The VIX prices magnitude, not direction, and low readings are not sell signals.