The "Greeks" are four numbers, calculated for every options contract, that describe how its price is expected to react to different changes — in the stock price, in time, and in volatility. You don't need calculus to use them; you need to know what each one is telling you.
Delta
Delta estimates how much an option's price moves for a $1 move in the underlying stock. A call with a Delta of 0.40 would be expected to gain roughly $0.40 for every $1 the stock rises. Delta also works as a rough, informal estimate of the probability an option expires in the money. See our full Delta explainer for a deeper walkthrough.
Gamma
Gamma measures how much Delta itself changes as the stock price moves. A high-Gamma option's Delta can shift quickly, which means its price sensitivity to the stock isn't constant — it accelerates as the option moves closer to the money. Gamma tends to be highest for at-the-money options close to expiration.
Theta
Theta measures how much value an option loses per day simply from time passing, all else equal — commonly called time decay. Theta is negative for option buyers (you lose a little value each day) and effectively positive for option sellers. Decay generally accelerates as expiration approaches. See our full Theta decay explainer for the details.
Vega
Vega measures how much an option's price changes for a 1-percentage-point change in implied volatility. Higher Vega means the option's price is more sensitive to shifts in the market's expectation of future volatility — which is why options often move in price even when the stock itself hasn't. See implied volatility explained for the concept Vega is reacting to.
Delta and Theta have dedicated deep-dive lessons on ScalpClock right now; Gamma and Vega don't yet have their own dedicated articles beyond this overview — that's a planned gap, not an oversight.
Why the Greeks Matter
Without the Greeks, an option's price change can look random. With them, it decomposes into understandable pieces: how much of a move was directional (Delta/Gamma), how much was lost to time (Theta), and how much came from a shift in volatility expectations (Vega). A trader who only watches the stock price and ignores the Greeks is missing most of what actually moves an option's price day to day.
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