Gamma is highest for at-the-money options nearest to expiration — which means 0DTE options carry the most concentrated gamma in the entire market. That single fact explains most of what makes same-day trading feel the way it does.

Concentrated gamma, intense hedging

Because 0DTE gamma is so concentrated, dealer hedging around same-day strikes is unusually intense — small moves in SPY force large, rapid hedging adjustments (how dealer hedging moves price). The huge daily volume in 0DTE options amplifies this further. The result is that dealer flow has an outsized grip on intraday price near those strikes.

Pins by day, fireworks by close

In a positive-gamma setup, this pins price hard to big 0DTE strikes — the market coils near a level for hours (gamma walls). But as expiration nears and gamma peaks into the afternoon, the hedging gets more violent, and in a negative-gamma regime the close can accelerate into a fast directional move (power hour).

On 0DTE, you're not just trading SPY — you're trading the dealer hedging that same-day gamma forces. Ignore it and the tape will feel random.

Why it's NoVo's edge

This is the core reason NoVo trades SPY, QQQ and IWM 0/1-DTE through a gamma lens: near the gamma-flip level, dealer positioning gives directional moves a real, measurable tilt (the gamma flip, positive vs negative gamma). It's also why the read gets less reliable far from the flip. See 0DTE trading.