Gamma, and the last week of a short option
Gamma measures how fast delta changes when the stock moves. It is the second derivative of the option price and it is largest at the money and close to expiry. For a seller it is the Greek that turns a manageable position into an unmanageable one over about four days.
Delta tells you where you stand. Gamma tells you how fast that is about to change, and it is the reason a position you understood on Monday can be something else entirely by Thursday.
What the number means
The UBER $72.50 call, 42 days out, carries a gamma of 0.0488.
Delta is 0.331. If the stock rises a dollar, delta becomes roughly 0.331 plus 0.0488, so about 0.38. Rise another dollar and it goes to about 0.43. The option gets more sensitive the more right it becomes, which is the whole idea.
At 42 days that is a slow drift. Now watch what happens to it.
Gamma over the life of the contract
| Days left | Gamma, at the money | Gamma, $72.50 strike | Delta, $72.50 strike |
|---|---|---|---|
| 42 | 0.0535 | 0.0488 | 0.331 |
| 21 | 0.0758 | 0.0599 | 0.246 |
| 7 | 0.1315 | 0.0585 | 0.101 |
| 3 | 0.2010 | 0.0283 | 0.024 |
| 1 | 0.3482 | 0.0009 | 0.000 |
The at-the-money column goes up by a factor of six and a half. On the final day, an at-the-money option's delta moves 0.35 for every dollar the stock travels, which means a two dollar move takes it from a coin flip to nearly all-in.
The $72.50 column tells the other half of the story. Our strike is out of the money and staying there, so its gamma peaks around 21 days and then dies. An option that is not going to be reached stops caring about anything.
So gamma is not simply "large near expiry". It is large near expiry at the strikes that are still in play, and vanishing everywhere else. The whole distribution of risk crowds into a narrower and narrower band around the stock price.
What that costs in dollars
Take an at-the-money short call and move the stock two dollars against you.
| Days left | Option before | Option after | Loss | Delta before and after |
|---|---|---|---|---|
| 42 | $312 | $430 | -$118 | 0.54 to 0.64 |
| 21 | $218 | $338 | -$120 | 0.53 to 0.67 |
| 7 | $124 | $252 | -$128 | 0.52 to 0.76 |
| 1 | $46 | $203 | -$157 | 0.51 to 0.96 |
Read the last row against the first. At 42 days the contract had $312 of premium in it and a two dollar move cost $118. On the final day there was $46 of premium left and the same move cost $157.
That is the trade nobody prices properly. In the last few days you are holding almost no premium and almost all of the risk. Your delta went from a coin flip to 0.96, meaning you are now effectively short 96 shares, and there was no moment where you decided to be.
Why sellers are always short gamma
Selling an option means selling convexity. Your profit is capped at the credit and your delta gets worse in whichever direction hurts.
Stock rallies against a short call: delta grows, so you get shorter as it climbs. Stock falls: delta shrinks toward zero, so you stop participating in the good outcome. Both directions move against you. That is negative gamma and it is not a bug in your trade, it is the thing you were paid $153 for.
Which explains the feeling every seller knows. Positions grind out small wins and then occasionally hand back weeks of them in an afternoon. That asymmetry is gamma, it is structural, and no strike selection removes it.
What to do about it
- Close early. The standard rule is to buy back at 50 to 80 percent of max profit rather than holding to expiry. The reason is on this page: the last 20 percent of the premium comes with the worst gamma in the contract's life. And on an out-of-the-money strike there is barely any decay left to collect anyway.
- Do not roll into expiry week. Rolling to a contract with seven days on it is choosing the highest-gamma part of the curve.
- Watch the strikes near the stock. A far out-of-the-money short has almost no gamma. Gamma risk is a function of distance, not just of time.
- Expect pin risk. A stock sitting right at your strike on expiration Friday has a delta oscillating between 0 and 1 all afternoon, and you will not know whether you were assigned until after the close.
OptionsKing scores every candidate strike on a deterministic 0 to 100 scale, blends that score with the return on the capital the trade ties up, and shows you the highest-ranked handful. There is no minimum score. How it works covers what the ranking does and does not tell you.
Questions people actually ask
What is gamma in options?
The rate at which delta changes for a one dollar move in the stock. A gamma of 0.0488 means a 0.331 delta call becomes roughly a 0.38 delta call after the stock rises a dollar.
Why is gamma highest near expiration?
Because an option close to expiry has to resolve to either 0 or 1 delta within days, so its delta must travel a long way in a short time. At-the-money gamma went from 0.0535 at 42 days to 0.3482 on the final day in the worked example.
What does being short gamma mean?
That your delta moves against you in both directions. Every option seller is short gamma, which is why short premium books produce many small gains and occasional large losses. It is the risk the credit pays for.
Should I hold short options to expiration?
Usually not. The final days carry the highest gamma of the contract life while holding the least premium, so you are taking the most risk for the smallest remaining reward. Closing at 50 to 80 percent of maximum profit is the common discipline.
Sources
Rules and thresholds above were checked against these documents on August 4, 2026. Exchange and broker rules change. Confirm anything you are about to act on with your own broker.
Keep reading
Do the math on your own trade
Every price in this article is an illustrative worked example, not a quote. Read The Greeks for the rest of the series, and the disclaimer before you act on any of it. Selling options carries real risk of loss, and the loss can be far larger than the premium you collected.