Gamma is the Greek nobody explains well, so here is the plain version. If delta is your speed, gamma is your acceleration: how fast delta itself changes as the stock moves. It is small and quiet most of the time, then suddenly the thing that matters most.
Picture driving. Delta is your speed. Gamma is how hard you are pressing the accelerator. Far from the strike the ride is smooth. Near the strike, close to expiration, the pedal gets touchy and small bumps throw you around.
Acceleration, not speed
Delta tells you how much your option moves per $1 of stock. But delta is not fixed, it shifts as the stock moves. Gamma measures how quickly it shifts. High gamma means delta can swing fast, so your exposure changes rapidly with even small moves in the stock. Low gamma means delta drifts slowly and predictably.
Why sellers respect it near expiration
Gamma is highest for options near the strike with little time left. That is exactly when a short option can flip from harmless to painful in a single move, because delta accelerates so fast. A position that felt calm on Monday can lurch on Friday afternoon. This is why many income sellers close or roll before the final days, to step out of the high-gamma zone.
A quick example
You sold a put sitting just out-of-the-money with two days left. Its delta is a modest 0.35, so it feels manageable. Then the stock drips down two dollars and crosses your strike. Because gamma is high here, that delta does not inch up, it leaps toward 0.70 almost at once. Suddenly the position moves twice as fast against you as it did an hour ago. Nothing changed but the stock nudging through the strike, and gamma turned a calm trade into a fast one.
Far away, gamma sleeps
The flip side is reassuring. When your strike is well away from the stock price, or there is still plenty of time on the clock, gamma is tiny. Delta drifts slowly and predictably, and there are no nasty lurches. This is part of why selling further out-of-the-money, with more time left, feels so much calmer: you are trading in the low-gamma flats, not on the cliff edge near the strike.
You do not need to track gamma tick by tick. Just respect the rule it teaches: options get twitchiest near the strike in the last few days. If you do not want that white-knuckle ride, do not hold short options into it.
- Gamma is the acceleration behind delta: how fast your exposure changes as the stock moves.
- It is highest near the strike with little time left, which is when short options get risky fast.
- Many sellers close or roll before the final days to avoid the high-gamma zone.
This article is educational and is not investment advice. Options involve risk, including the possible loss of principal. Examples and premiums shown are illustrative and change with the market. Practice with paper trading before committing real money.