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Options glossary · the market's estimate of future movement, baked into an option's price
Implied volatility (IV) is the market's expectation of how much a stock will move, expressed as an annualized percentage and embedded in every option price. It says nothing about direction; it is purely a price on movement. The more movement traders expect, the more an option costs, and vega is how that expectation translates into price.
IV rises before known events like earnings and collapses once the uncertainty resolves, the phenomenon behind IV crush. It also varies by strike and expiry (the volatility skew), so read it from the exact contract you are pricing, not a single number for the whole stock.
Use the IV shown on your broker's option chain for the specific contract, since it varies by strike and expiry. Index options often run 12 to 20%, large-cap stocks 25 to 50%, and pre-earnings contracts can exceed 100%.