The Greeks: A First Look

In short

Delta, theta, gamma, and vega each isolate one way an option's price responds to the stock, time, or volatility, previewing the deeper Risk Management course.

The Greeks are just a set of numbers describing how an option's price reacts to change — here's a first, plain-English look at all four.

Four numbers, four kinds of change

An option's price doesn't move like a stock's — it reacts to several things at once: the stock's movement, time ticking toward expiration, and shifting expectations of volatility. The Greeks each isolate one of those effects so you can reason about them individually instead of guessing at a tangled-together price change. This is a first orientation; the full mechanics live in the Risk Management & The Greeks course.

Greek	What it measures, in one line
Delta	How much the option's price moves for a $1 move in the stock
Theta	How much value the option loses per day just from time passing
Gamma	How much delta itself changes as the stock moves
Vega	How much the option's price moves for a change in implied volatility

Worked example: a feel for delta and theta

A call option with a delta of 0.40: if the stock rises $1, the option's price would be expected to rise roughly $0.40, all else equal. Traders also lean on delta as a rough, informal estimate of the odds that option finishes in the money.

An option with a theta of -0.05: all else equal, it's expected to lose about $0.05 of value for every day that passes — even if the stock doesn't move an inch. This is the same "time value erodes" mechanic from the expiration lesson, just given a number.

Key takeaway: Delta measures your sensitivity to price, theta measures your sensitivity to time — both are estimates under current conditions, not guarantees.

Delta and theta are the two beginners meet first; the next lesson looks at both more closely, together.

This lesson is educational content explaining standard options mechanics, not personalized investment or trading advice.