What is Gamma in options?
The accelerator behind Delta — and the reason expiration week feels so violent.
Gamma (Γ) measures how much an option's Delta changes for a $1 move in the underlying stock — it's the rate of change of Delta itself. A call with 0.40 Delta and 0.05 Gamma should see its Delta rise to roughly 0.45 if the stock rises $1. Gamma is highest for at-the-money options and grows sharply as expiration approaches, which is exactly why near-the-money contracts close to expiry can swing in value so violently on small stock moves.
Delta's rate of change
If Delta tells you an option's current sensitivity to the stock, Gamma tells you how quickly that sensitivity itself is shifting. A low-Gamma option's Delta barely budges as the stock moves — the position behaves predictably. A high-Gamma option's Delta can swing hard with a small move, meaning the position's whole risk profile can change meaningfully within a single session.
Why it's a friend to buyers, an enemy to sellers
For a long option, Gamma works in your favor: as the stock moves toward profitability, Delta grows in that same direction, so gains compound. As it moves against you, Delta shrinks, so losses decelerate. For a short option, it's the mirror image — Delta grows against the position as the stock moves the wrong way, which is precisely the risk premium option sellers are paid to take on. This is also why Gamma is the central risk in strategies like short strangles and iron condors: calm markets collect steady Theta, but a sharp move can turn losses non-linear fast.
A worked example
Say SPY trades at $560 and an at-the-money call shows Delta 0.50 and Gamma 0.04. If SPY rises to $562, Delta should rise to roughly 0.50 + 2 × 0.04 = 0.58. Now the option is behaving more like 58 shares of stock than 50 — its sensitivity to the next dollar move just increased, purely because of Gamma. Near expiration, that same at-the-money contract's Gamma can be several times higher, which is why 0DTE positions can flip from calm to explosive within minutes. OptionScope's Gamma Flip Heatmap extends this same idea to the whole market — mapping where dealer hedging flips from stabilizing to destabilizing.
Common mistakes
Assuming a hedge stays a hedge. A Delta-neutral position built at one stock price can develop meaningful net Delta after a move, purely from Gamma — hedges need rebalancing, not just setting once.
Underestimating short-Gamma risk in calm markets. Premium-selling strategies can look steady for weeks and then lose fast on one sharp move — that tail risk is exactly what the steady income was compensating for.
Ignoring Gamma in expiration week. At-the-money Gamma peaks in the final days before expiry, which is why pinning and violent last-minute swings both happen more often right before contracts expire.
Try it live
The Gamma below is real — pulled from a live option contract (strike nearest spot, ~30–45 days to expiry) on OptionScope's real CBOE-fed chain. Look up any symbol:
Explore the full Greeks Lab — free →
Related: All 5 Greeks explained · Delta · Theta · Gamma exposure (GEX)