What does the VIX measure?

The VIX is built from a wide range of SPX put and call prices with about 23 to 37 days to expiration, weighted to estimate expected volatility 30 days ahead. Like any implied volatility, it comes from what traders pay for options: when they pay more for protection, the VIX rises. The SPX vs SPY options guide explains the index options behind it.

To turn the number into a move, a common rule of thumb divides it by about 16, close to the square root of the roughly 252 trading days in a year. A VIX of 16 implies a typical daily move of about 1% for the S&P 500; a VIX of 32, about 2%. It is a one-standard-deviation estimate, not a limit, and bigger days happen.

VIX
The Cboe Volatility Index: the 30-day implied volatility of the S&P 500, calculated from SPX option prices and quoted as an annualized percentage.
Spot VIX
The index value you see on a chart. It cannot be traded directly; VIX futures and options are separate contracts with their own prices.
Contango
A futures curve where later months trade above nearer ones and above spot. VIX futures are in contango most of the time.

Why does the VIX go up when stocks go down?

When the S&P 500 falls sharply, investors rush to buy puts for protection and option sellers demand more premium, so implied volatility rises. Falling markets also tend to swing more than rising ones. That is why the VIX and the S&P 500 usually move in opposite directions, as in the drawing at the top of this page.

It is a tendency, not a rule. The VIX can rise along with stocks when traders buy calls in a fast rally or hedge ahead of a big event, and it can drift lower during a slow decline. A low VIX does not mean the market cannot drop, and a high VIX does not mark a bottom by itself.

What is a high VIX? Calm and stressed readings

There are no official thresholds, but common conventions help: readings below about 20 are usually described as calm, 20 to 30 as elevated, and above 30 as stress. Since 1990, the VIX has averaged roughly 19 to 20, and in some quiet years it stayed below 15 for months at a time.

At the extremes, the VIX closed at a record 82.69 on March 16, 2020, as the COVID-19 crash hit and market-wide circuit breakers halted trading several times that month. Its previous closing peak, just over 80, came in November 2008 during the financial crisis. Spikes like these have tended to fade as fear eases, but the timing varies: after 2008 the VIX stayed high for months.

Turn your phone sideways to read the drawing. Tap to close.

A hand-drawn VIX number line from 10 to 85: a green zone below 20 labeled calm, a yellow zone from 20 to 30 labeled elevated and a red zone above 30 labeled stress. A dashed marker near 20 points to the long-run average, 19–20. Two flags at the far right mark the record close of 82.69 on March 16, 2020 and the earlier peak just over 80 in November 2008. A note reads conventions, not official thresholds.

Can you buy the VIX? Futures, ETPs and contango

No. The VIX is an index calculated from option prices, so there is nothing to own. Traders get exposure through VIX futures and options and through exchange-traded products (ETPs) that hold VIX futures, and none of them tracks the spot VIX you see on a chart.

The reason is the futures curve. Most of the time, futures for later months trade above the spot VIX, a shape called contango, because the market prices in some turbulence ahead. A fund that holds short-dated futures keeps selling the expiring contract and buying the next, pricier one, and each future tends to slide toward spot as it nears expiration. Over long periods, products tracking short-term VIX futures have lost most of their value this way, and their issuers describe them as short-term trading tools.

In a panic the curve can flip into backwardation, with near months above later ones, and these products can jump. That jump is why people buy them; timing it is the hard part. Some VIX ETPs are leveraged or inverse, which adds daily-reset risk and can wipe out most of a position in one violent day.

Turn your phone sideways to read the drawing. Tap to close.

Two hand-drawn panels. Left: a VIX futures curve in contango, a black dot for spot VIX and hollow orange dots for months M1 to M5 rising to the right, with red arrows showing each future sliding toward spot. Right: an illustrative long-VIX ETP line that drifts down over time, labeled roll cost drags it down, with one brief jump in a panic.

How to use the VIX in your trading

Use the VIX as context, not as a buy or sell signal. It tells you how big swings in the index are likely to be, which feeds straight into stop distance and position size, the core of risk management.

Hypothetical: you risk $200 per trade on a $500 index ETF. With the VIX at 16 (about ±1% a day), a stop 1.5% away is $7.50 a share, so 26 shares. With the VIX at 32 (about ±2%), that stop sits inside normal noise; doubling it to $15 cuts the size to 13 shares. Same dollar risk, half the shares, as the drawing below shows.

  • Rising VIX: wider stops, smaller size, fewer trades; spreads on stocks and options often widen too.
  • Options: a high VIX means expensive index options. Buyers pay more; sellers collect more but carry bigger risk. Vega, one of the options Greeks, measures that sensitivity.
  • A single stock can have high implied volatility around its own earnings while the VIX stays low, so check the stock itself.
  • Check the VIX before CPI, jobs and Fed days on the economic calendar; it can rise into big events.

Turn your phone sideways to read the drawing. Tap to close.

Two hand-drawn columns for a hypothetical $500 index ETF. VIX 16: a daily range of about ±1% drawn as a grey band, a dashed stop at 492.50, $7.50 below price, and a position bar of 26 shares. VIX 32: a band twice as wide (±2%), the stop at 485.00, $15 below, and a bar of 13 shares. A yellow note reads same risk: $200.