September's Coin Flip Arrives With Dealers Short Gamma and SPY Pinned

September has a dirty little secret: over the last 40 years it has delivered a coin-flip win rate of exactly 50% and an average return of -0.61%, making it the worst calendar month for equities by expected value. That baseline alone should reshape how aggressively you press directional bets this month.

Layer in the current GEX picture — SPY sitting on a net negative gamma of -$5.3 billion with max pain pinned at 760 — and the setup is one where dealers are forced to trade WITH momentum, not against it. That means moves, when they come, can extend further and faster than the casual observer expects. GammaBrief's SPY model has been right 7 of 9 calls (78%) over the last 42 days. We intend to use that edge carefully in a month that rewards patience over bravado.