Volatility · Market indicators
The VIX Explained: What the Volatility Index Measures and How to Read It
The VIX is Cboe’s volatility index. It uses S&P 500 option prices to work out how much the market expects the index to move over the next 30 days, and quotes that as an annualised percentage. A VIX of 20 does not mean “a 20% loss”; it means options are pricing volatility of about 20% a year, roughly ±5.8% over a month.
By Daniel Berg ·
Example: VIX at
20
- Expected move per year
- ±20%
- Per month (÷ √12)
- ≈ ±5.8%
- Per trading day (÷ 16)
- ≈ ±1.25%
- Applies to
- S&P 500, next 30 days
Rules of thumb for one standard deviation. Markets are not normally distributed; large moves happen more often than the formula suggests.
What exactly does the VIX measure?
The VIX does not measure past price moves but an expectation: the implied volatility of the S&P 500 over the coming 30 calendar days. Implied means the number is derived from option prices. When investors pay up for puts and calls on the index, the VIX rises; when options get cheaper, it falls. Our implied volatility guide explains the concept in general.
Cboe has calculated the index with today’s method since 2003, using a wide range of out-of-the-money S&P 500 options: puts below the current level and calls above it. Two expirations that bracket the 30-day mark are used and interpolated, so the result is always a constant 30-day horizon. The method does not rely on a particular pricing model such as Black-Scholes.
The VIX earned the nickname “fear index” because it typically rises when stocks fall. In sell-offs investors buy puts for protection, which pushes implied volatility up. Rising markets, by contrast, usually come with a falling VIX. That negative relationship is a tendency, not a law: there are stretches when the index and the VIX rise together.
Reading VIX levels: from the number to an expected move
Because the VIX is annualised, you have to scale it down to your time frame. Volatility grows with the square root of time. For one month, divide by √12 ≈ 3.46; for one trading day, divide by √252 ≈ 16. That is where the “rule of 16” comes from: a VIX of 16 implies an expected daily move of about ±1%.
| VIX | Expected daily move | Expected monthly move | Typical environment |
|---|---|---|---|
| below 15 | below ±0.95% | below ±4.3% | Calm market, cheap protection |
| 15–20 | ±0.95–1.25% | ±4.3–5.8% | Normal conditions |
| 20–30 | ±1.25–1.9% | ±5.8–8.7% | Elevated uncertainty, jumpy news flow |
| above 30 | above ±1.9% | above ±8.7% | Stress, heavy demand for protection |
For context: over long periods the VIX has averaged a little under 20, with the median lower still. In acute crises it has shot far above 50; in autumn 2008 and in March 2020 it closed above 80. In very calm periods such as 2017 it briefly dropped below 10. For your own reading, comparing it with the recent past is often more useful than a fixed threshold.
Worked example: what a VIX of 20 means for the S&P 500
Round assumptions for teaching purposes, not a current index or VIX level.
- S&P 500
- 5,000 points
- VIX
- 20
- Horizon
- 30 days
- Measure
- 1 std. dev.
1Monthly range
20% ÷ √12 ≈ 5.8%. On 5,000 points that is about ±290 points: an expected range of roughly 4,710 to 5,290 over 30 days.
2Daily range
20% ÷ 16 = 1.25%, or about ±63 points on a typical trading day.
3VIX rises to 30
The expected monthly range widens to about ±8.7%, or ±430 points. Index options become noticeably more expensive because buyers are paying for a larger possible move.
4VIX falls to 12
The monthly range shrinks to about ±3.5%, or ±175 points. Protection through puts becomes cheap, and so does the premium option sellers collect.
The VIX does not say where the index will go, only how much movement the options market is pricing right now. Whether that expectation was too high or too low is only clear afterwards.
VIX vs realised volatility: expectation and reality
Realised (historical) volatility measures how much the index actually moved. The VIX measures how much it is expected to move. The two differ systematically: most of the time the VIX sits above the volatility that then materialises. That gap is called the volatility risk premium.
The reason is demand for insurance. Many investors hedge their stock holdings with index puts and are willing to pay more than the mathematically fair value for them. Option sellers demand a premium for carrying that risk. As a result, selling options collects premium on average, but with rare and very large losses when realised volatility suddenly explodes.
- VIX well above realised: the market prices more movement than recently occurred, often after a shock, when fear fades more slowly than the price action.
- VIX near or below realised: rare, and usually when markets are already swinging hard. Protection is then not expensive relative to the actual movement.
- Volatility reverts to the mean: very high VIX readings rarely last long, whereas very low ones can persist for months.
What the VIX means for your option prices
The VIX is the implied volatility of one index. For options on the S&P 500, the SPY ETF and similar index products it is a direct pricing input: when the VIX rises, the time value of those options rises, which is what the Greek vega measures. Individual stocks have their own implied volatilities. They often move in the same direction as the VIX but sit at a different level and depend heavily on company events such as earnings; see IV crush.
High VIX
Options are expensive. Defined-risk premium strategies such as credit spreads or the iron condor collect more. Buyers need bigger moves to reach a profit.
Low VIX
Options are cheap. Protection through puts or a collar costs less. Sellers collect little premium for the same risk and should size positions accordingly.
Rising VIX
Long options gain through vega and short options lose, often at the same time as the price moves against put sellers. That is when short-volatility positions suffer most.
The VIX is also only an average across many strikes. Far out-of-the-money index puts usually carry higher implied volatility than calls; that is the volatility skew. When you value a specific option, look at its own IV, not just the VIX.
Can you trade the VIX? Futures, options and ETPs
You cannot buy the VIX itself; it is a calculated index. What trades are VIX futures, VIX options and exchange-traded products that track futures. These instruments follow the spot VIX only loosely, because a future reflects expected volatility at a later date.
- Contango is the normal state: in calm periods later VIX futures trade above earlier ones. Products that keep rolling into the next future lose value in the process, even if the VIX does not move.
- Backwardation in stress: in a sell-off short-dated futures trade above longer ones, which is read as a sign of acute fear.
- VIX options are priced off the future, not the spot VIX, and settle to a special opening quotation. They therefore behave differently from what the current VIX would suggest.
Common misconceptions about the VIX
“A low VIX means a crash is coming”
A low VIX shows calm and cheap protection. It can stay low for months. It tells you that hedging is cheap, not when to time anything.
“VIX 30 means a 30% loss”
The VIX is an expected range in both directions, annualised. VIX 30 is roughly ±8.7% over a month as one standard deviation.
“The VIX applies to every stock”
It only measures the S&P 500. Single stocks, the DAX or crypto have their own volatility, which can differ a lot from the VIX.
“A VIX ETP tracks the VIX”
These products hold futures, not the index. In contango they lose money even if the VIX stays where it is.
Frequently asked questions
What is the VIX in simple terms?
The VIX is a Cboe index that uses option prices to estimate how much the S&P 500 is likely to move over the next 30 days. It is quoted as an annualised percentage. A high VIX means investors are paying a lot for options and protection; a low VIX means the market expects calm.
What is a normal VIX level?
Over long periods the VIX has averaged a little under 20. Readings below 15 are considered calm, 20 to 30 elevated and above 30 stressed. These are rules of thumb; comparing with the last few months is often more telling, because the level shifts across market regimes.
How do I convert the VIX into an expected move?
For a monthly range divide the VIX by about 3.46 (the square root of 12), and for a trading day divide by 16 (roughly the square root of 252). A VIX of 20 therefore implies about ±5.8% per month and ±1.25% per day, each as one standard deviation, not a maximum.
Why does the VIX rise when stocks fall?
In falling markets investors buy puts for protection and expected volatility rises. Both push up the prices of index options and with them the VIX. In rising markets demand for protection fades and the VIX usually falls. The relationship is strong but not without exceptions.
Can you buy the VIX directly?
No, the VIX is a calculated index. VIX futures, VIX options and products that track futures are tradable. Because futures usually trade in contango, long products lose value through the roll over time, even if the VIX does not change.
Is there a VIX for European indices?
Yes. The VDAX-NEW measures the expected 30-day volatility of the DAX from DAX options, and the VSTOXX does the same for the Euro Stoxx 50. They read the same way as the VIX, though their levels differ.
Where to go next
All numerical examples in this guide are rounded, illustrative assumptions, not market data. The content is educational and not investment advice. Options are complex instruments; you can lose the entire amount invested, and more than that when selling options.