Implied Volatility (IV)

IV is not directly observable — it is "implied" by the current market price of an option. The process works backward from the options pricing model.

The concept: The Black-Scholes model takes five inputs (stock price, strike price, time to expiration, risk-free rate, and volatility) to calculate a theoretical option price. Since we can observe the actual market price, we plug it in and solve for the missing variable — volatility. That solved volatility is the implied volatility.

What IV represents: An IV of 40% means the options market expects the stock to move within a +/-40% range over the next year, with roughly 68% probability (one standard deviation). For a $100 stock with 40% IV, the market expects price to be between $60 and $140 in one year.

Daily expected move: To convert annual IV to a daily expected move, divide by the square root of 252 (trading days per year): Daily expected move = Stock Price x (IV / sqrt(252)). For a $100 stock with 30% IV: $100 x (0.30 / 15.87) = $1.89 expected daily move.

IV is forward-looking: Unlike historical volatility (which measures past price movements), IV captures the market's collective expectation of future movement. This distinction matters — IV often rises before anticipated events (earnings, FDA decisions) even when the stock has been calm.

IV Rank measures where current IV falls within its high-low range over the past year. Formula: IV Rank = (Current IV - 52-week Low IV) / (52-week High IV - 52-week Low IV) x 100. If IV ranged from 20% to 60% over the past year and current IV is 40%, IV Rank = (40-20)/(60-20) = 50.

IV Percentile measures what percentage of days in the past year had lower IV than today. If current IV is higher than IV on 75% of trading days in the past year, IV Percentile = 75.

Why they differ: IV Rank is sensitive to outliers. If IV spiked to 100% for one day during a crash, the 52-week high is 100% — making the IV Rank appear low even when IV is elevated relative to normal conditions. IV Percentile is more robust because it counts days, not extremes.

Trading application: Use IV Rank above 50 (or IV Percentile above 60) as a threshold for premium-selling strategies (iron condors, credit spreads, covered calls). Below those levels, consider premium-buying strategies (long straddles, long calls/puts) since options are relatively cheap.

IV crush is the rapid decline in implied volatility — and therefore option premiums — after a known event occurs, most commonly earnings.

Why it happens: Before earnings, uncertainty is high. The options market prices in a large expected move because the stock could gap up 10% on a beat or down 10% on a miss. This uncertainty inflates IV. After the report, regardless of which direction the stock moves, the uncertainty is resolved — IV drops sharply, often 30-50% in a single session.

The trap for beginners: A trader buys a call option before earnings, the stock rises 3%, but the option loses value because IV dropped 40%. The IV crush overwhelmed the directional gain. This is the most common options mistake new traders make.

How to avoid it: Check IV rank before buying options ahead of earnings. If IV rank is above 70, options are expensive and you are likely overpaying for the expected move. Selling premium (iron condors, straddles) is often more profitable in high-IV environments because IV crush works in the seller's favor — the premium they collected evaporates after earnings.

Key metric: Compare the expected move (derived from at-the-money straddle price) to the stock's average actual earnings move over the past 8 quarters. If the expected move is $8 but the stock typically moves only $5 on earnings, selling premium has a statistical edge.

Historical Volatility (HV) measures how much the stock actually moved in the past. It is calculated as the standard deviation of daily returns over a lookback period (typically 20 or 30 days), annualized.

Implied Volatility (IV) measures how much the market expects the stock to move in the future, derived from current option prices.

The spread matters: When IV is significantly higher than HV (IV/HV ratio above 1.2-1.3), options are relatively expensive — the market expects larger future moves than what has recently occurred. This is common before earnings or major events. Premium sellers thrive in this environment.

When IV is below HV (IV/HV ratio below 0.8), options are relatively cheap — the market is underpricing future movement. This happens during quiet periods after major selloffs. Premium buyers (long straddles, long options) benefit here.

Mean reversion: IV tends to revert to its historical average. After an IV spike (e.g., during a market selloff), IV gradually normalizes as fear subsides. After an IV collapse (e.g., post-earnings), IV gradually rebuilds as new uncertainties emerge. This mean-reverting behavior is the foundation of most volatility trading strategies.