Gamma and Vega: The Other Two Greeks, Made Simple
You already know delta and theta. The last two Greeks, gamma and vega, are the supporting cast. Gamma is how fast your delta changes, and vega is how much volatility moves your price. Both are simpler than they sound.
- Gamma: how fast your delta changes, the acceleration behind the speed
- Vega: how much your price reacts to changes in volatility
- When each one bites hardest, near expiration or around big events
- How all four Greeks work together as a team
In the last two lessons you met the two Greeks you will use most: delta, your option's speed against the stock, and theta, the daily melt of time. That is most of the battle. The two left, gamma and vega, are the supporting cast, and they are easier than their reputations.
Think of driving a car. Delta was your speed. Now meet the gas pedal and the weather. One changes how fast your speed itself can shift, the other changes how the whole road behaves. Let us take them one at a time.
Gamma: The Acceleration of Delta
Back in Lesson 12 you learned delta, but with a quiet asterisk: delta does not stay put. As the stock moves, delta moves too. Gamma is the Greek that measures how fast delta changes.
If delta is your speed, gamma is your acceleration. Apple is at $200 and your $200 call has a delta of 0.50. Apple climbs to $201, and the delta does not stay at 0.50, it rises to maybe 0.53. That jump of 0.03 is gamma at work. The next dollar nudges delta again.
Gamma is largest for at-the-money options near expiration. There, a small move in the stock can swing delta hard, so the option's whole character shifts quickly, from strolling to sprinting in a single afternoon. Deep in-the-money and far out-of-the-money options have low gamma, because their delta is already pinned near 1.00 or near zero and has little room to move.
Vega: Sensitivity to the Market's Nerves
Vega is about a force you already know: volatility, the choppiness from Lesson 8 that fattens an option's hope value. Vega measures how much your option's price moves when volatility changes.
When the market gets nervous and expects bigger swings, volatility rises, extrinsic value swells, and option premiums climb, even if the stock has not moved at all. When the market calms down, volatility falls and those premiums deflate. Vega tells you how strongly your particular option reacts to that mood shift.
This is the secret behind the earnings surprise from Lesson 8. Before an earnings report, everyone braces for a big swing, volatility spikes, and a high-vega option gets expensive. After the report, the uncertainty is gone, volatility collapses, and that same option can lose value even if the stock rose. That was vega draining away. Like gamma, vega is largest for at-the-money options, and it grows with more time left on the clock.
When Gamma and Vega Bite Hardest
You do not need to track these two every day. You just need to know when they take over.
Gamma rules the final days. An at-the-money option in its last week has huge gamma, so its delta lurches around and its price can swing violently on small stock moves. Vega rules around events and longer time frames. If you hold an option through earnings, or for many months, volatility shifts can move your price as much as the stock does.
When I was advising clients, the wildest rides were always near expiration. An at-the-money option in its final days has so much gamma that its delta jumps around, and the price can swing hard on a tiny move in the stock. Beginners found it equal parts thrilling and terrifying. Once they understood it was simply gamma doing its job, the terror turned into respect, and they stopped holding those lottery tickets into the last day by accident.
All Four Greeks, One Team
Step back and the whole picture is clean. Each Greek measures the option's reaction to one force in the world.
Delta reacts to the stock's price. Theta reacts to the passing of time. Gamma reacts to changes in delta itself. Vega reacts to changes in volatility. That is the entire core team. You do not need to do their math, your broker shows every one of these numbers. You just need to know what each is telling you, and now you do.
- Gamma is the acceleration of delta: how fast your delta changes as the stock moves.
- Vega is your price's sensitivity to volatility, the market's expected choppiness.
- Both peak for at-the-money options; gamma bites near expiration, vega around events and over longer time frames.
- The four Greeks each measure the option's reaction to one force: price, time, delta's change, and volatility.
Pop Quiz
Three quick questions to see what stuck. Pick an answer and the explanation shows up right away.
Gamma measures what?
If delta is speed, gamma is acceleration: it measures how quickly delta itself changes as the stock moves.
Vega measures your option's sensitivity to what?
Vega tracks volatility. When the market expects bigger swings, premiums swell; when it calms, they deflate. Vega measures how strongly your option reacts.
Both gamma and vega are largest for which kind of option?
Both peak at the money. That is where delta can swing most (gamma) and where the most extrinsic value sits to react to volatility (vega).
Bottom Line
Gamma and vega round out the core Greeks. Gamma is the acceleration of delta, biggest at the money and near expiration, where an option's behavior can change in a hurry. Vega is your sensitivity to volatility, biggest at the money with time to spare, and the reason options can move on the market's mood alone.
Put them with delta and theta and you have the full team: four numbers, each measuring the option's reaction to one force. You no longer have to wonder why a price moved. You can name the Greek behind it.
Next up: How Option Prices Move. You now know every force on an option's price. Next we put them all together and watch a real price move, so you can finally read the whole story at once.