# Why the Market Pins on Fridays ## SPX DAILY GEX LEVELS Computed from daily-settled Cboe open interest. Dealer positioning is modeled, not observed. Nothing here is advice. Open interest settlement: 2026-09-24. - **Call wall, settled 2026-09-24. Computed from daily-settled Cboe open interest.** $7,800 - **Put wall, settled 2026-09-24. Computed from daily-settled Cboe open interest.** $7,500 - **Zero-gamma flip, settled 2026-09-24. Computed from daily-settled Cboe open interest.** $7,670 - **Vol trigger, settled 2026-09-24. Computed from daily-settled Cboe open interest.** $7,709 - **Net dealer gamma, settled 2026-09-24. Computed from daily-settled Cboe open interest.** $15.06B - **Largest absolute gamma strike, settled 2026-09-24. Computed from daily-settled Cboe open interest.** $8,000 Source: SquawkFlow URL: https://squawkflow.com/learn/why-the-market-pins-on-fridays Category: Market Structure Published: 2026-09-22 Updated: 2026-09-22 Type: Explainer > Friday is not special as a weekday. It is where option expirations have been concentrated for decades, and the concentration is what pinning needs. --- ## The short answer Friday is not special as a day of the week. It is special because it is where option expirations were put. Pinning is an expiration effect. It needs a large block of open interest at one strike that is about to stop existing, and hedging against that block that gets more sensitive as the clock runs out. The weekday carrying the most expiring open interest is the weekday where the condition is met most often, and for decades that has been Friday. [Gamma pinning](/glossary/gamma-pinning) covers the mechanism itself, and [pin risk](/learn/pin-risk-options-expiration) covers what it means for someone holding a contract near the strike. This page is about the calendar. ## The listing convention, in one paragraph Standard monthly equity and index options expire on the third Friday of the month. Weekly options, when they were added, were listed to expire on Fridays as well. The result is a calendar where a normal month has four or five Friday expirations, one of which carries the monthly tranche and is far larger than the others. [OpEx](/glossary/opex) covers the monthly date and why the third Friday accumulates so much open interest. Nothing about Friday causes pinning. The accumulation causes pinning, and the accumulation happens to land on Fridays. ## What changed for index options The Friday answer is now only half true, and the half that expired is the index half. SPX has listed expirations on every weekday since 2022, when the Tuesday and Thursday series completed the set. That means the front expiration, the book that stops existing at today's close, exists on a Wednesday exactly as it does on a Friday. The daily cycle described in [0DTE gamma exposure](/learn/0dte-gamma-exposure) runs five times a week. What it looks like in practice: on Tuesday 2026-09-22, at a capture taken at 3:14pm Eastern with spot near 7,767, the SPX front expiration carried 350,350 contracts of open interest, settled the prior evening, spread across 229 strikes carrying gamma, and a net dealer gamma of about 18.3 billion dollars per one percent move in spot, summing the gamma the chain publishes for each contract. That is a real same-day book, on a day of the week that had no expirations at all a few years ago. An earlier version of this paragraph also quoted a front-expiry call wall and put wall fifteen points apart. Those levels were withdrawn on 2026-09-22, the day they shipped, because an audit found the wall ranking at minutes to expiry is forced onto the strike beside spot by the at-the-money gamma term rather than by where the open interest sits. Quoting them as evidence of a narrow book would have been quoting the method back at itself. The open interest, the strike count and the net gamma above are measured and stand. Single-stock and ETF options did not follow index options onto a daily cycle in the same way. For most listed names the weekly expiration is still Friday, so the classic Friday question is now mostly a single-stock question, while the index version has become a daily one. ## The Thursday wrinkle nobody expects For the monthly index tranche, the biggest block of the month, the Friday framing is wrong by a day. Cboe's contract specifications for the standard AM-settled SPX option state that trading ordinarily ceases on the business day preceding the day the exercise settlement value is calculated, which is usually the Thursday. The settlement value itself is built from opening prices on Friday morning. The PM-settled SPXW series, which is what most same-day and weekly activity uses, trades until 4:00pm Eastern on the expiration day itself. So on a monthly expiration week there are two distinct events with two distinct clocks: an AM-settled tranche whose hedging requirement is finished by Thursday's close, and a PM-settled tranche that runs to Friday's bell. Attributing a Friday tape entirely to open interest that stopped trading the previous afternoon is a common misreading. [What settles on a triple witching day](/learn/triple-witching-explained) works through both windows for the four quarterly sessions, and the [expiration calendar](/calendar) carries the dates. ## What a pin needs beyond a Friday Concentration is necessary and not sufficient. Three other conditions have to hold, and each of them fails regularly: - **The open interest has to be large relative to what trades in the underlying.** A strike carrying meaningful size in a name that turns over many multiples of it is not going to anchor anything. - **Price has to be near the strike already.** Pinning describes the last part of a journey, not the journey. A gap that opens two percent away from the largest strike leaves nothing to pin to. - **The positioning assumption has to hold.** The mechanism requires hedgers to be positioned such that their rebalancing leans against moves away from the strike. Flip that assumption and the same open interest produces the opposite behaviour. Nobody publishes who holds which side. [Max pain](/learn/max-pain-theory-options) covers the strike most often quoted in this context and what the pinning claim attached to it does and does not support. ## How to check it rather than believe it The version of this question that can be answered with data is narrow: on expiration days, how far from the largest same-day strike did the index actually close, in points, and how does that compare with a non-expiration day? The [free SPX gamma page](/gex) prints the all-expiry call wall, put wall and flip; its front-expiry block shows only the withdrawal notice described above. The [gamma heatmap](/gex-heatmap) shows the strike-by-expiration grid, including the largest same-day strike this test needs. Logging the distance for twenty sessions produces a number with a sample size attached, which is a different kind of object from a story about the Fridays it worked. Two limits travel with all of it. The open interest behind these levels is settled data from the prior close, so a position opened this morning is not in it. And dealer positioning is an assumption rather than an observation, which is the condition the whole mechanism rests on. *Educational content, not financial advice. See our [risk disclosure](/risk-disclosure).* --- ## Common questions ### Why do stocks pin to strikes on Fridays? Because Friday is where option expirations concentrate. Pinning is an expiration effect rather than a weekday effect, and the weekday that carries the most expiring open interest carries the most of it. ### Is the pin bigger on the third Friday? The third Friday of the month is the standard monthly expiration, so it carries the largest open interest of any expiration in a normal month. The four quarterly sessions, where index futures and index options settle alongside stock options, are larger still. ### Do index options still mostly expire on Friday? No. SPX has listed expirations on every weekday since 2022, so the same-day book exists Monday through Friday. Single-stock options remain concentrated on Fridays. --- ## Citation Source: SquawkFlow, https://squawkflow.com/learn/why-the-market-pins-on-fridays Retrieved: 2026-09-26 21:45 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.