S&P 500 Monday After OPEX May 2026: What History Says About the Session That Follows a 1% Friday Selloff

# S&P 500 Monday After OPEX May 2026: What History Says About the Session That Follows a 1% Friday Selloff

> **Quick answer:** The S&P 500 fell 1.14% on OPEX Friday May 15, 2026 — the first meaningful pullback from record highs above 7,500. Historically, the Monday after monthly options expiration averages a nearly flat -0.02%, meaning no clear directional edge exists. But the post-OPEX *week* is different: markets typically move roughly 2% in either direction once the gamma pinning constraints expire. Monday May 18 carries five live catalysts — Musk-OpenAI jury deliberations, Lebanon ceasefire deadline, a 4.55% 10-year yield, Warsh's first full week in the chair, and a historically common delta-hedge reversal within one to two weeks of an OPEX selloff.

The S&P 500 ended OPEX Friday, May 15, 2026 down 1.14% from its all-time closing record of 7,501.24, set just 24 hours earlier. The Nasdaq fell 1.62%. For investors heading into the weekend, the question is the same one traders ask every third Friday of the month: what does Monday look like from here?

The historical answer is more nuanced than the simple "bounce or continue lower" binary. Post-OPEX Monday has almost no average directional bias — but the surrounding week does. Here is what the data and five specific live catalysts say about the session opening on Monday, May 18.

## What the Data Actually Shows About Post-OPEX Mondays

The most important number for Monday morning is deceptively boring: the average S&P 500 return on the Monday immediately following monthly options expiration is approximately **-0.02%** — essentially zero. That figure, drawn from multi-decade backtests of the option-expiration week effect, tells you that history provides no reliable directional edge for this specific session.