Two of the option greeks do most of the work on a short-term trade. Delta is how much the option's price moves per $1 in the underlying. Gamma is how much that delta itself changes as the underlying moves. Speed and acceleration (the greeks, explained).

Delta: the speed

An at-the-money option has a delta around 0.50 — it moves about $0.50 per $1 in SPY. Deep in-the-money, delta approaches 1.00 (moves nearly dollar-for-dollar); far out-of-the-money, it approaches 0 (barely moves). Delta is your current sensitivity to price (delta explained).

Gamma: the acceleration

Gamma tells you how fast delta changes. High gamma — as on a 0DTE at-the-money option — means delta ramps quickly as price moves your way: the option gets more sensitive the more right you are, so gains accelerate. The catch: it works in reverse too, accelerating losses when you're wrong.

Delta is how fast you're moving. Gamma is how fast that speed changes. On 0DTE, gamma is so high the trade goes from crawl to sprint in a heartbeat.

Why the pair defines a scalp

High gamma is the reason a 0DTE scalp can explode in your favor on a small move — and evaporate just as fast against you (why gamma matters for 0DTE). It's also why the same gamma that helps you helps dealers move the market when they hedge it (how dealer hedging moves price). Pair delta and gamma with theta's decay and you've got the full picture of a same-day trade (theta decay).