The Greeks

L’insieme delle misure — delta, gamma, theta, vega, rho — che descrivono come il prezzo di un’opzione reagisce a prezzo, tempo, volatilità e tassi.

The Greeks are a set of numbers that tell you how an option's price is expected to move when something changes. Delta measures how much the premium shifts for a one-dollar move in the underlying, theta how much value you lose each day as expiration approaches, vega your sensitivity to changes in implied volatility, and gamma how fast delta itself changes. Together they turn a vague feeling about a trade into something you can actually measure.

In practice you use them to size and shape a position rather than to predict direction. Say you buy a call with a delta of 0.40: it behaves roughly like 40 shares, so if the stock rises one dollar the option gains about forty cents, before theta and volatility muddy the picture. A theta of -0.05 means you bleed about five dollars a day per contract if nothing moves.

The common mistake is treating the Greeks as fixed. They drift constantly as price, time and volatility change, so a delta-neutral position at open can be badly skewed by the afternoon. Check them as live readings, not as a promise the option will keep.

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