# OPEX (Options Expiration) Source: SquawkFlow URL: https://squawkflow.com/glossary/opex Category: Options Greeks Published: 2026-08-25 Type: Definition > Monthly and quarterly options expiration, how third-Friday SPX settlement actually works, and what genuinely changes when a large block of gamma expires. --- ## What OPEX means OPEX is trader shorthand for options expiration, most often the monthly expiration on the third Friday, when the largest block of listed open interest in the market comes off the board at once. Options now expire on almost every trading day, but the third Friday still concentrates far more contracts than any daily or weekly expiration, which is why it retains a name of its own. The [OPEX calendar 2026](/calendar) lists those dates with the exchange source behind each one. ## The monthly and quarterly calendar Standard monthly equity and index options expire on the third Friday of each month. Four of those twelve are quarterly expirations, and Cboe defines the term plainly: "Triple Witching" refers to "the simultaneous expiration of individual stock options, equity index options and equity index futures that occurs four times a year on third Fridays in March, June, September and December." Cboe adds that on these days "there is often an observed increase in trading volume and market volatility as traders close, roll out or offset their expiring positions." Note what that claim is and is not. Elevated volume and volatility are directionless. Nothing in the mechanics says which way price goes. ## The settlement detail that catches people out Standard third-Friday SPX options are A.M.-settled, a change Cboe completed in 1992 after SEC concerns about P.M.-settled index options moving the cash market into the close. Two consequences follow, and both surprise people. First, these contracts stop trading before their expiration date. Per Cboe's specifications, "Trading in SPX options will ordinarily cease on the business day (usually a Thursday) preceding the day on which the exercise-settlement value (i.e., the expiration date) is calculated, 5:00 pm ET." You cannot trade out of a standard SPX position on Friday morning. Thursday's close is your last exit. Second, settlement is not Friday's open or close. It is the Special Opening Quotation, or SET, built from the official opening trade price of each of the 500 constituents, which do not all open at once. Because the SOQ is assembled from opening prints rather than a continuous index calculation, it can land outside the day's traded range entirely. Cboe measured this: across quarterly A.M.-settled expirations from March 2009 through March 2024, SOQ values "fell outside the high and low range of the S&P 500 Index... approximately 30% of the time, most often above the daily high." The full detail is in Cboe's paper on [settlement of standard, A.M.-settled S&P 500 index options](https://cdn.cboe.com/resources/spx/Settlement_of_Standard_AM_Settled_SP_500_Index_Options.pdf). ## What actually changes when the gamma expires The durable, mechanical effect of OPEX is subtraction. A large block of open interest simply ceases to exist on Friday, and every hedging obligation attached to it disappears with it. Before expiration, contracts clustered at heavily-traded strikes can anchor price, because the parties who are short those options must hedge more actively the closer spot sits to the strike and the nearer expiration comes. That is the mechanism behind [pin risk](/learn/pin-risk-options-expiration) and behind the gravitational pull described by [max pain theory](/learn/max-pain-theory-options). The [SPX max pain strike for each listed expiration](/spx-max-pain) is free to check against spot in the sessions running into an OPEX. After expiration, that anchoring is gone. A level that had held for three weeks can stop functioning the following Monday, not because sentiment shifted but because the open interest creating it was retired. This is also why post-OPEX weeks often feel different. Whatever dampening or amplifying effect the expiring positioning was exerting is removed, and the remaining book is smaller and differently distributed until new positions accumulate. One caution matters more than any of this. Dealer positioning is an assumption, never an observation. Open interest tells you a contract exists; it never tells you which side a dealer is on. Every OPEX narrative built on "dealers are long gamma here" rests on a sign convention that may be wrong at any given strike. ## Is OPEX bullish or bearish? Neither, reliably. The honest answer is that OPEX changes a constraint rather than a direction. Beware explanations that assert a seasonal edge without publishing a hit rate, the interesting question is not whether a level exists but how often it has held when price actually tested it. We publish no such rate on our [free SPX gamma exposure page](/gex), for that exact reason: the one we showed until August 2026 counted the days price never came near a level alongside the days it genuinely tested one. The levels are there with the time they were captured, and the [glossary](/glossary) covers the [zero gamma level](/glossary/zero-gamma) that OPEX so often relocates. *Educational content, not financial advice. See our [risk disclosure](/risk-disclosure).* --- ## Citation Source: SquawkFlow, https://squawkflow.com/glossary/opex Retrieved: 2026-09-11 00:31 ET Attribution: cite the page URL rather than a copied number. Levels are recomputed every session, so a number without its date is wrong within a day. SquawkFlow publishes market-structure data and education. Nothing here is investment advice, a price target or a recommendation, and we have no order execution.