What is Implied Volatility?
Implied volatility (IV) is the volatility level that current option prices imply for a stock over a given time period, expressed as an annualized percentage. Unlike historical volatility (which measures past price movement), implied volatility refers to the period ahead: it is derived from the current market price of options using an options pricing model like Black-Scholes. It describes what option prices embed, not what the stock will do.
Put another way: if a stock's options have an implied volatility of 30%, option prices are consistent with a one-standard-deviation annualized move of roughly 30% in either direction. To convert this to a daily figure, divide by the square root of 252 (trading days per year). A 30% IV corresponds to a one-standard-deviation daily move of approximately 1.9%.
How IV is Calculated
IV is not directly observed; it is "implied" by working backward from the option's market price. Given the stock price, strike price, time to expiration, interest rate, and dividend yield, the Black-Scholes model can calculate a theoretical option price for any given volatility input. IV is the volatility value that, when plugged into the model, produces the option's actual market price.
In practice, brokers, trading platforms, and data providers display IV alongside the option chain, so it is rarely calculated by hand. The sections below cover what the number means and what it does not.
Why IV Matters
Of the inputs to an option's price, IV is the only one not quoted in the market, which is why it is the number traders use to describe an option as priced high or low. Two options can have the same strike, same expiration, and same underlying stock, but if one is priced during a calm market (low IV) and the other during a volatile market (high IV), their prices will be very different.
High IV means option premiums are large relative to the stock price: option prices embed large price moves. A seller of options collects more premium, and a buyer pays more for the same exposure. Whether the move that follows is larger or smaller than the one priced in is not something IV itself says.
Low IV means option premiums are small: option prices embed small price moves. A buyer pays less for exposure to price movement, and a seller collects less for taking it on. Low IV can stay low or rise sharply, and the number alone does not indicate which.
IV Rank and IV Percentile
Raw IV numbers are hard to compare across stocks. A biotech with 80% IV might be normal, while a utility stock with 30% IV might be unusually high. To normalize this, traders use:
IV Rank: Where current IV falls within its 52-week range. If IV ranged from 20% to 60% over the past year and is currently at 40%, the IV rank is 50%. That places current IV in the middle of its historical range.
IV Percentile: The percentage of days in the past year where IV was lower than today's level. If IV percentile is 85%, current IV is higher than 85% of the past year's readings. Unlike IV rank, it accounts for how much time was spent at each level, so a single spike in the past year does not compress it.
IV Crush
IV crush occurs when implied volatility drops sharply, typically after a known event like an earnings announcement. Before earnings, uncertainty is high, so IV rises (options become expensive). After the announcement, the uncertainty resolves, and IV drops, often dramatically.
IV crush matters most to option holders. An option can lose value even when the stock moves in the holder's direction. For example, a call bought before earnings can be worth less after the stock rises 2% if IV falls from 80% to 40% at the same time, because the volatility component of its price shrank by more than the move added.
Option sellers are on the other side of the same effect. Short straddles, short strangles, and iron condors opened before an announcement gain from the drop in IV, and they lose if the stock moves further than the options were pricing in. Which side comes out ahead depends on the size of the actual move relative to the implied one, which is not known in advance. Earnings options strategies describes how each structure pays.
Volatility Skew
IV is not uniform across all strikes. Out-of-the-money puts typically have higher IV than at-the-money options, creating the "volatility smile" or "smirk." This reflects demand for downside protection: the market prices large declines as more likely than a normal distribution would. Skew shows how one strike's IV compares with the other strikes in the same chain.
IV is a measurement, not a prediction. High IV does not mean the stock will move a lot; it means option prices embed that possibility. Reading IV, IV rank, IV crush, and skew together shows how an option's price compares with its own history, with other strikes, and with the move the market has priced in.