What Is Implied Volatility?
Implied volatility, often shortened to IV, is the volatility figure that makes a model's theoretical option price equal the price actually trading in the market. Rather than measuring how much a stock has moved in the past, it reflects how much movement option buyers and sellers collectively expect over the life of the contract, expressed as an annualized percentage.
A stock with 30% implied volatility is priced as if the market expects its annualized standard deviation of returns to be 30%. That is fundamentally different from historical or realized volatility, which is computed from past price data. Comparing the two is a common starting point for volatility trading strategies.
How Implied Volatility Is Derived
Every other input to an option pricing model is observable: the stock price, the strike, time to expiration, interest rates, and expected dividends. Volatility is the one unknown, so traders take the market price of the option and solve backward for the volatility that reproduces it. Because there is a formula in only one direction, this is done numerically rather than algebraically.
In practice IV is not a single number for a stock. Options at different strikes and expirations trade at different implied volatilities, producing the volatility smile and skew. Equity index options typically show higher IV for downside strikes because investors pay up for crash protection, a pattern that became pronounced after the 1987 market crash.
Why Implied Volatility Matters
IV is the language of options desks. Traders quote and think in volatility terms rather than dollar prices, because vol is what they are really buying and selling. When implied volatility is high relative to what the trader expects to be realized, selling options is attractive; when it is low, buying them is. Events like earnings announcements cause IV to build up beforehand and collapse afterward, a phenomenon known as vol crush.
The concept also shows up far beyond derivatives desks. The VIX index is simply a weighted measure of 30-day implied volatility on S&P 500 options, and it is watched globally as a gauge of market fear. Interviewers for trading roles frequently test whether candidates understand that option prices encode expectations, so a working grasp of IV is close to mandatory for markets recruiting.
