VIX — CBOE Volatility Index¶
OVERVIEW¶
The VIX is the CBOE Volatility Index — the market's real-time estimate of how much the S&P 500 will move over the next 30 calendar days, expressed as an annualized percentage. It is constructed from the prices of S&P 500 index options (SPX) across a wide range of strikes and two expiration dates using a model-free methodology.
Quick Reference
A VIX reading of 20 implies ±20% annualized volatility, which converts to approximately ±5.77% per month and ±1.26% per day.
HOW IT WORKS¶
Calculation Methodology¶
The CBOE interpolates between the two nearest monthly SPX option expirations to produce a constant 30-day implied volatility. Unlike the original 1993 VIX — which relied on a single at-the-money strike — the current version aggregates pricing across the full options chain.
| Variable | Definition |
|---|---|
| T | Time to expiration |
| F | Forward price of the S&P 500 |
| K₀ | First strike below F |
| Kᵢ | Each strike in the options chain |
| Q(Kᵢ) | Midpoint of bid/ask for the option at that strike |
Volatility Conversions¶
| Time Horizon | Formula | VIX 20 Example |
|---|---|---|
| Daily (1σ) | VIX ÷ √252 | ±1.26% |
| Weekly (1σ) | VIX ÷ √52 | ±2.77% |
| Monthly (1σ) | VIX ÷ √12 | ±5.77% |
REFERENCE LEVELS¶
Historical Benchmarks¶
| Date / Period | VIX Level | Implied Daily Move (SPY) | Context |
|---|---|---|---|
| March 16, 2020 | 82.69 | 5.21% | COVID crash — exceeded 2008 peak |
| 2008 Financial Crisis | ~80.86 | ~5.09% | Previous all-time high |
| Full Year 2017 | 11.1 avg | 0.70% | Historic low-volatility regime |
2020 vs. Reality
During the March 2020 spike, actual SPY moves that week were −11.98%, −4.94%, and −5.18% — realized volatility exceeded even the elevated implied level. In 2017, realized volatility averaged 6.7% annualized while VIX implied more, demonstrating that options were expensive even at historically low levels.
HOW TO USE¶
By Trader Type¶
| Trader Type | VIX Signal | Strategy Application |
|---|---|---|
| Options — Premium Seller | VIX elevated | Sell straddles, iron condors; position for IV crush |
| Options — Premium Buyer | VIX depressed | Buy options; position for volatility expansion |
| Equity Trader | VIX > 30 | Contrarian long signal; historically co-occurs with market bottoms |
| Macro Hedger | Any | Buy VIX futures or VIX calls to hedge equity portfolio dislocations |
Contrarian Use Case
VIX readings above 30 have historically co-occurred with equity market bottoms as fear peaks. The index functions as a sentiment gauge rather than a directional predictor.
LIMITATIONS¶
| Limitation | Detail |
|---|---|
| Implied ≠ Realized | VIX measures expectations, not outcomes. Implied volatility overstates realized volatility approximately 70% of the time. |
| Not directional | A rising VIX does not mechanically cause the S&P 500 to fall, though the two are strongly negatively correlated. |
| ETP decay | Products like UVXY and VIXY suffer severe daily decay from rolling short-dated VIX futures and do not track spot VIX over multi-day holds. |
| Intraday noise | Intraday VIX spikes can be brief and fully reverse by the close. |
VIX ETPs
UVXY and VIXY are not proxies for the spot VIX. Contango in VIX futures causes persistent roll decay that erodes value in long-vol ETP positions held beyond intraday timeframes.