OPEX (Options Expiration)

What Is OPEX?

OPEX—short for options expiration—refers to the date on which options contracts expire. On expiration, contracts are either exercised (if in-the-money and the holder chooses to or has automatic exercise instructions), settled in cash, or expire worthless. After expiration, the contract no longer exists.

Options expire on a schedule. The original options market operated on monthly expirations: the third Friday of each month was (and remains) the standard monthly expiration for equity options. Over time, weekly expirations were introduced, followed by daily expirations on major indices and ETFs. The full OPEX calendar now includes:

• Monthly OPEX: Third Friday of each month. The largest by notional value; the cycle that dominates institutional positioning and GEX analysis.
• Weekly OPEX: Every Friday (plus Monday and Wednesday for some underlyings). Shorter-dated, smaller notional, but increasingly significant in aggregate.
• Daily OPEX (0DTE): Zero-days-to-expiration contracts that expire the same day they are traded. Available on SPX, SPY, QQQ, and a growing list of names.

Why It Matters for Options Traders

OPEX is not just a calendar date—it is a market event that reshapes dealer positioning, gamma sensitivity, and price behavior in the days surrounding it.

As contracts approach expiration, gamma accelerates for near-the-money strikes. Dealers who sold options must hedge more aggressively as the underlying moves, because their delta exposure changes faster near expiration. This creates the feedback loop underlying gamma squeeze and pin risk dynamics: heavy open interest at a specific strike can attract the underlying price as dealers hedge, and violent moves can cascade if strikes are crossed.

The expiration event itself resolves open interest. After monthly OPEX, the total open interest in expiring contracts goes to zero. This reset affects the gamma exposure (GEX) profile—the net hedging pressure dealers face changes substantially after large open interest clears. Traders who track GEX monitor how the post-OPEX profile differs from pre-OPEX to anticipate changes in market behavior in the following week.

The rise of 0DTE trading has extended OPEX dynamics to every session. A significant portion of SPX and SPY options volume now expires the same day it trades, meaning the gamma concentration and pinning effects that once clustered around Fridays now occur with daily frequency.

Key Characteristics

• Monthly OPEX: Third Friday of each month—the primary expiration cycle for institutional positioning
• Weekly expirations: Every Friday, plus mid-week on major indices—extended the OPEX effect across the calendar
• 0DTE (daily) expirations: Same-day expiry available on SPX, SPY, and select ETFs—creates intraday gamma dynamics
• Gamma acceleration near expiry: Gamma rises sharply for near-the-money strikes as contracts approach expiration, amplifying price sensitivity
• Pinning effect: Heavy open interest at a strike can attract the underlying price as dealer hedging creates stabilizing pressure
• Open interest reset: All expiring contracts are removed from open interest after expiration—the GEX and dealer positioning landscape shifts materially
• Settlement timing: Most equity options settle using Friday opening prices for monthly contracts; 0DTE SPX settles on the same-day close