What is implied volatility in options?
Implied volatility is the annualized volatility of the underlying that, when fed into an options pricing model, reproduces an option's current market price. It is not measured from past prices; it is backed out of what buyers and sellers are paying today. That makes it the market's price for future movement, and the single most important input in deciding whether an option is cheap or expensive.
How it is derived
An options pricing model such as Black-Scholes takes five main inputs: the underlying price, the strike, the time to expiry, interest rates and volatility. Four of those are observable. The fifth, volatility, is not. So the model is run backwards: given the option's market price, what volatility would make the model produce that price? That number is the implied volatility.
Because each strike and expiry trades at its own price, each has its own implied volatility. The pattern of those numbers across strikes is the skew or smile; across expiries it is the term structure. When people quote a single implied volatility for a stock, they usually mean at-the-money volatility for a particular expiry, or a blended index of several.
Implied volatility is quoted as an annualized percentage. A stock with 30 percent implied volatility is being priced as if its one-standard-deviation move over a year were about 30 percent of its price.
Turning it into a daily or weekly move
Volatility scales with the square root of time. To convert annualized implied volatility to a daily figure, divide by the square root of the number of trading days in a year, about 252, whose square root is close to 15.9. A stock with implied volatility of 16 percent is therefore priced for a one-standard-deviation daily move of roughly 1 percent.
For a week, divide by the square root of 52, about 7.2. Implied volatility of 36 percent becomes roughly a 5 percent one-standard-deviation weekly move. Under a normal distribution, about 68 percent of outcomes fall within one standard deviation, though real returns have fatter tails than that, so larger moves occur more often than the normal curve suggests.
These conversions are the basis of the expected move, the range the options market is pricing for a given period. They are approximations, but they are the fastest way to translate an abstract percentage into dollars on the chart.
What makes implied volatility move
Supply and demand for options. When traders rush to buy protection, implied volatility rises because option prices rise. When they sell options to collect premium, implied volatility falls. The model does not know why prices changed; it only reports the volatility that matches them.
Scheduled events. Implied volatility on contracts that span an earnings report, a central bank decision or a major data release is usually elevated, because the event adds a known source of risk. After the event, that premium disappears quickly, which is the IV crush familiar to anyone who has bought options before earnings.
Market direction. In equities, implied volatility tends to rise when prices fall and fall when prices rise. Declines are typically faster and more disorderly than rallies, and demand for protection spikes during them. That inverse relationship is one of the most stable patterns in the options market.
Why it matters to every option trade
Two traders can be right about direction and get very different results depending on the implied volatility they paid. Buying a call at high implied volatility means paying a large premium for movement; if the stock rises less than priced, or volatility falls, the call can lose money despite the stock going up.
Implied volatility also feeds every dealer positioning model. Gamma, vanna and charm all depend on it, so the same open interest can produce a different gamma map on a high-volatility day than on a calm one.
The most useful way to judge implied volatility is relative: against the stock's own history, against the volatility the stock is actually delivering, and against other expiries and strikes. A single implied volatility number in isolation says little about whether options are expensive.
Implied volatility indices
Some implied volatility measures are published as indices. The best known is the VIX, which estimates the 30-day implied volatility of the S&P 500 from a strip of SPX option prices across many strikes, rather than from a single at-the-money contract. Similar indices exist for other benchmarks and for different horizons, such as nine days and three months.
An index like this is useful as a single summary of what the options market is charging for a broad market, and its level converts to an expected move in the same way as any other implied volatility. A VIX reading of 16 implies a one-standard-deviation daily move of about 1 percent in the S&P 500. It is still a price, not a forecast, and it can stay high or low for long periods.
Common questions
What is a high implied volatility?
It is relative. Broad indices often trade in the teens or twenties, while many single stocks trade far higher. Compare a reading with the stock's own history using IV rank or IV percentile.
Does high implied volatility mean the stock will move a lot?
It means the market is paying for a large move. Whether the move happens is a separate question; implied volatility has historically tended to exceed realized volatility on average.
How do I convert IV to a daily move?
Divide annualized implied volatility by about 15.9, the square root of 252 trading days. An IV of 32 percent implies roughly a 2 percent one-standard-deviation daily move.
Implied volatility is the volatility backed out of an option's market price. Divide it by about 15.9 for a one-standard-deviation daily move, and always judge it relative to the stock's own history and to realized volatility.
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