Options Greeks Explained: Delta, Gamma, Theta, Vega
The Greeks measure how an option price reacts to price moves, time, and volatility. We explain delta, gamma, theta, and vega in plain language and why they matter.
The dashboard of an option
An option price does not move one-for-one with the stock. It reacts to several forces at once β the stock price, the passage of time, and changes in volatility. The Greeks are the gauges that measure each force separately, like the dials on a dashboard. Learn to read them and an option stops feeling like a black box.
Delta β sensitivity to price
Delta tells you how much the option price moves for a $1 move in the underlying.
- A call has a delta from 0 to +1; a put from 0 to β1.
- A delta of 0.60 means the option gains about $0.60 when the stock rises $1.
- Traders also read delta loosely as the rough probability the option finishes in the money.
Gamma β how delta itself changes
Gamma measures how fast delta changes as the stock moves. High gamma means your delta shifts quickly β the option accelerates in your favor when right, but flips against you fast when wrong. Gamma is largest for near-the-money options close to expiry, which is what makes short-dated options so twitchy.
Theta β the cost of time
Theta is time decay: how much value the option loses each day, all else equal. It is negative for buyers (you bleed a little daily) and positive for sellers (you collect it). Theta accelerates as expiry approaches β this is why buying short-dated options is a race against the clock.
Vega β sensitivity to volatility
Vega measures how much the option price moves when implied volatility changes by one point. Buyers are long vega (they profit when volatility rises); sellers are short vega. This is why an option can lose money even when the stock moves your way β if volatility collapses at the same time.
Why the Greeks matter
The Greeks explain the "why" behind a confusing option P&L: you were right on direction (delta) but lost to time (theta) or a volatility drop (vega). They also let you build positions that are neutral to one force and exposed to another β the foundation of every serious options strategy. Options are advanced and risky; understand the Greeks before risking real money.
Conclusion
The Greeks are the gauges of an option: delta (sensitivity to price), gamma (how delta changes), theta (time decay), and vega (sensitivity to volatility). Together they explain why an option gains or loses even when the stock does something you did not expect. Reading them turns options from a guess into a measured position β essential before trading them.
Next step
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