The Greeks are a set of risk metrics that describe how an option's price changes in response to different market variables. If you trade 0DTE options on SPX, SPY, or QQQ, understanding the Greeks isn't optional — they're the mechanics behind every level you see on the GEX heatmap.
Every level on StrikeGEX exists because of the Greeks. The king node is a function of gamma. The walls are a function of delta hedging. The speed at which price moves through a zone depends on whether dealers are long or short gamma. If you understand the Greeks, you understand why the levels work — not just that they work.
Delta measures how much an option's price moves for each $1 move in the underlying. A call with 0.50 delta gains $0.50 when SPX rises $1. For dealers, delta is the hedge ratio — it tells them how many shares or futures to buy or sell to stay neutral. When aggregate delta shifts at a strike, dealers must rebalance, and that rebalancing is the flow that moves price.
Gamma measures how fast delta changes. High gamma means the hedge ratio is shifting rapidly, forcing dealers to constantly adjust. This is the Greek behind everything you see on the StrikeGEX heatmap — positive gamma (yellow) creates mean-reverting, sticky zones. Negative gamma (purple) creates fast, trending zones where dealers amplify the move instead of dampening it.
Theta is the cost of holding an option over time. For 0DTE traders, theta is extreme — options lose value rapidly throughout the session. This is the silent tax on every position. But theta also drives dealer behavior: as options expire and gamma concentrates, the hedging flows become more aggressive near key strikes.
Vega measures how much an option's price changes when implied volatility moves. When VIX spikes, vega-heavy positions gain value. When vol collapses, they lose. For day traders, vega matters most at the open — the vol crush (or expansion) in the first 30 minutes sets the tone for how aggressively dealers need to hedge.
The Greeks don't operate in isolation. Here's how they combine during a typical 0DTE session:
You don't need to compute Greeks manually. StrikeGEX processes live options chain data and translates dealer gamma exposure into the color-coded levels on your heatmap. But knowing what's behind those colors helps you understand why a level holds, why it breaks, and when the regime is about to shift.
Dive deeper into each Greek with the individual guides below:
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