The zero-gamma flip
One level, two different markets
The zero-gamma flip is the SPX price where aggregate measured dealer gamma crosses zero. Above or below it, dealer hedging can have different feedback on price moves. It is a regime boundary, not a support, resistance, or trading instruction.
What Is the Zero-Gamma Flip? Shown on a Real SPX Session — 53 seconds, on a real session. Watch on YouTube
Sum dealer gamma across every strike and you get a curve that depends on where the index is trading. At some price that curve crosses zero. That crossing is the zero-gamma flip — also called the gamma flip line, the gamma flip point or simply the zero-gamma level — and it separates two mechanically different markets.
Above the flip, dealers are net long gamma. Their hedging sells rallies and buys dips — a stabilising flow that tends to compress ranges and pin price near heavy strikes. Below the flip, dealers are net short gamma. Now the hedging buys rallies and sells dips, adding to whatever momentum exists. That is the textbook mechanism. On our archive it shows only in the tape-signed measured book (short gamma there comes with higher volatility over the next half hour, t 5.0 over 1,108 sessions); on the volume book the chart draws, the flip sits about ten points from price and its side carries no measured effect on what volatility does next (t 1.1).
What the flip is not
The flip is not support, not resistance, and not a trade signal. Price crosses it freely — what changes is the feedback around every subsequent move. This site tested directional signals on years of this data and found nothing worth an arrow: the sign of net GEX alone carries no reliable edge. What the flip does tell you is which regime the tape is operating in, and how seriously to take a breakout or a fade.
Where it sits today
Today's flip is on /now, free and fifteen minutes behind the tape. The flip moves through the day as flows accumulate — on the terminal it is the FLIP line, recomputed every second while the market trades. Every archived session shows where it was at the close and how price behaved around it; the summary on each session page states the close's distance from the flip in points. Related: what GEX is and the walls that anchor the gamma profile.