Implied volatility is the volatility input that makes an option-pricing model reproduce a specified market price for an option. The option premium is observed; implied volatility is inferred by solving the model backward. It is usually quoted on an annualized basis, with the exact convention determined by the market and pricing model.
A price-implied parameter, not an observed statistic
An option model relates premium to inputs such as the underlying or forward price, strike, time to expiration, interest rates, dividends where relevant, and volatility. If the other inputs are fixed, a higher option premium generally maps to a higher implied volatility. This inversion is why implied volatility can move even when the underlying price barely changes: the option market may be repricing uncertainty, event risk, hedging demand or other factors embedded in the premium.
Implied volatility therefore differs fundamentally from Realized Volatility. Realized volatility is calculated from price changes that actually occurred over a historical window; implied volatility is extracted from option prices for a remaining future horizon. It is forward-looking because it is derived from prices attached to that future horizon, but those prices can also incorporate volatility risk premia, supply and demand, and other pricing effects. Implied volatility is therefore not a promise that subsequent realized volatility will equal the quoted number. The comparison becomes meaningful only after matching the horizon and measurement convention.
Why an underlying does not have one implied volatility
A single underlying can have many simultaneous implied volatilities. Options with the same expiration but different strikes often map to different values, producing the cross-sectional pattern associated with Volatility Skew. Options with different expirations can imply different volatility levels across time, forming a Volatility Term Structure. Saying that “implied volatility is 25%” is therefore incomplete unless the relevant strike or moneyness, expiration and convention are understood.
The less obvious practical point is that implied volatility is also model- and data-dependent. Two systems can start from the same market and report different values if they use different pricing models, interest-rate or dividend assumptions, underlying or forward inputs, settlement versus live quote prices, or interpolation methods. That does not automatically mean one value is wrong; it means implied volatility is a derived coordinate for option prices rather than a directly observed market quantity. For research, comparisons and backtests, the model, price source, strike selection and expiration methodology should be kept consistent before differences in implied volatility are interpreted as differences in the market pricing of volatility.