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What is the difference between implied and realized volatility?
Implied volatility and realized volatility both put a number on how much an asset moves, and both are quoted as an annualized percentage, but they point in opposite directions in time. Implied volatility is forward-looking: the volatility figure solved backward from an option premium. Realized volatility is backward-looking: the standard deviation of the returns an underlying actually produced over a completed window, annualized by the square root of the number of periods in a year.
The distinction is not academic. Implied volatility is a price the market is charging right now for future movement. Realized volatility is a record of movement that already happened. They describe the same stretch of time only after an option horizon has fully elapsed, which is why comparing them requires care about windows and dates.
How implied and realized volatility are measured
A model such as Black-Scholes-Merton takes volatility as an input and returns a price, so to find implied volatility the market price is treated as known and the model is inverted to find the single volatility that reproduces it. Pricing engines find it numerically, searching for the volatility that makes the model match the premium. Solve from a live, two-sided quote: a stale print or a price outside the model’s bounds returns no usable volatility. Each contract carries its own implied volatility, and reading those values across strikes and expirations builds the skew, smile, and term structure traders watch.
Realized volatility is a direct statistic. The standard close-to-close method takes daily returns, computes their sample standard deviation, and multiplies by the square root of the assumed trading days in a year, commonly 252. For a short series of daily log returns of +1.0%, −0.5%, +1.5%, −1.0%, and +0.5%, the mean is 0.3% and the sample standard deviation, dividing by four for five returns, is 1.04% per day, which annualizes to 1.04% × √252, or 16.5%. Change the lookback, the return interval, or the treatment of overnight gaps and the number changes, so state the method with the figure. Cboe’s methodology states the conventions for its own realized-volatility indices; compare like windows rather than mixing estimators.
How implied and realized volatility differ in practice
Neither measure carries direction. A 60% implied volatility says the market prices a wide range of outcomes without saying up or down, and a high realized volatility can come from a stock that finishes flat after repeated large reversals.
The two also respond to different forces. Implied volatility moves on option supply and demand, hedging flows, approaching expiration, and above all scheduled events. It rises into earnings and can collapse the moment the report clears, an effect known as volatility crush. Realized volatility moves only as new return observations enter the window and old ones roll out, so one large day can lift a short lookback and then drop it just as suddenly when that day exits.
How traders compare implied and realized volatility
Traders rarely pick one. They pair them. Implied volatility judged against the underlying’s own history tells them whether options look rich or cheap before committing to a direction. Realized volatility over the option’s life tells them whether that premium was justified. A delta-hedged long option generally benefits when realized movement outruns premium, decay, and execution costs, and a short option generally benefits when realized movement stays contained, though a single gap can dominate an average comparison.
Over long samples, implied volatility has averaged above the realized volatility that followed. In Cboe’s May 2019 summary, average VIX was 19.3% versus 15.1% average realized volatility over 1990–2018. That is a long-run SPX index average, so measure the spread on your own contract and horizon before you trade it. The spread measures the premium after the fact, and a delta-hedged position’s cash result also turns on the realized path, gamma weights, jumps, funding and costs. When IV sits above past realized volatility, check the calendar before calling it rich: the option prices the movement ahead, including any event inside its life.
Bottom line
Implied volatility is the market’s forward price for movement, solved from an option premium and read across the chain as skew and term structure. Realized volatility is the backward-looking record of what the underlying actually did over its lookback and sampling interval. Fix the horizon, align the windows, and respect the volatility risk premium before concluding that implied and realized volatility were out of line.
Common questions
Implied Volatility vs Realized Volatility: FAQ
- Which is bigger, implied or realized volatility?
- On average implied volatility tends to sit above subsequently realized volatility. That gap is the volatility risk premium, and it compensates option sellers for bearing gap and tail risk. Because the premium is structural, compare the gap with its usual size before calling it a mispricing. In any single episode either can be larger: the market can price 50% implied volatility and the underlying can go on to realize far more or far less.
- Do implied and realized volatility tell you direction?
- No. Both measure the size of movement, not its sign. A high implied volatility reading means the market is pricing a wide range of outcomes in either direction, and a high realized volatility reading means returns were widely dispersed. A stock can finish near where it started after large reversals and still record high realized volatility, and skew can make one side of the option chain more expensive without implied volatility itself forecasting direction.
- How do traders trade implied versus realized volatility?
- They compare the implied volatility paid or collected at entry with the realized volatility the underlying delivers over the option’s life. A delta-hedged long option generally benefits when realized movement is large enough to outrun premium, decay, and execution costs, while a short option generally benefits when realized movement stays contained. The horizons and sampling must align: comparing a 30-day implied measure with a five-day realized spike mixes different windows and produces a misleading read.
- Why can implied volatility be high while realized volatility is low?
- Implied volatility rises into scheduled uncertainty such as earnings because the market prices a wider range of outcomes. Until the event happens, the underlying may drift quietly, so realized volatility stays low. Once the report lands and the uncertainty resolves, implied volatility usually falls sharply, an effect called volatility crush, even as realized volatility jumps on the reaction. This is why a trader can be right about direction and still lose money if the move is smaller than the premium priced beforehand.