What is OPEX, and why does monthly expiration move markets?

By Faizan Ahmad. Updated 2026-11-01.

OPEX is options expiration day. The big one is monthly OPEX, the third Friday of each month (next: November 20, 2026, then the December 18 quarterly), when standard stock, ETF and index options expire together. It can move markets because a large share of open options, and the dealer hedges tied to them, disappear at once. Price often gets held near big strikes in the days before, and once those hedges come off, the market can move more freely afterward.

When is OPEX?

If the third Friday is an exchange holiday, the expiration moves to the business day before. Cboe's 2026 calendar marks November 20 and December 18 as standard expirations. Daily expirations are covered in what are 0DTE options.

The SPX settlement wrinkle

Standard monthly SPX options are AM-settled. They stop trading the day before, usually Thursday (November 19 this month), and settle on a special opening quotation built from each S&P 500 stock's opening trade price on Friday morning. That settlement value can differ from where the index trades at any moment that morning. PM-settled SPX weeklys trade until 4:00 PM ET on expiration day.

Why does monthly expiration move markets?

• Gamma piles up near expiry. As expiration approaches, the gamma of near-the-money options rises sharply, so dealer hedging near big strikes gets heavier. When dealers are long that gamma, their hedging holds price near the strike. Ni, Pearson and Poteshman (Journal of Financial Economics, 2005) found that on expiration dates, closing prices of stocks with listed options cluster at strike prices.
• Then it all expires at once. When the options go, so do the hedges against them. Gamma that was damping moves, or amplifying them, is gone, and the walls and gamma flip can jump to new levels the next session.
• Rolling adds volume. Traders close expiring positions and reopen them in later months, which concentrates trading around the date.
• Settlement creates its own flows. In-the-money stock and ETF options turn into shares, and AM-settled index options settle on Friday's opening prints.

These are tendencies, not rules. A big news day beats expiration mechanics every time.

Where the big money sits: October 30, 2026

The day's eight biggest single options prints were all in standard monthly expiries. Seven were SPX options for the December 18 quarterly expiration, about $1.91B of premium between them, and the eighth was the 52,800-contract Nvidia January 15, 2027 $180 call block for $172.81M.

Big positions like these gather in monthly and quarterly expiries, which is why those dates carry more weight than an ordinary Friday. Several of these prints came in matched pairs at the same minute (the 7000 calls and 8000 puts at 10:42 AM and 1:52 PM), the signature of multi-leg trades; how to read spreads in the flow explains why they shouldn't be read as two separate bets.

October 30 was itself an expiration day: weekly options on stocks and ETFs, and the end-of-month expiration for index options. It's a good reminder of the limits of expiration magnets: SPY closed $7.88 below its $765 max pain for that expiry. The full check is in what is max pain.

What changes after OPEX?

The positioning map resets. Strikes that dominated dealer gamma can vanish, a market that felt stuck in a range can start trending, and a market that was being pushed around by negative gamma can calm down. Some traders talk about a "window of weakness" in the days after monthly expiration. Treat that as lore to test, not a rule: what matters is how much gamma actually rolled off and which way it was leaning.

How to prepare for OPEX

• Know what expires. Check open interest by strike for that date, not just across all dates.
• Check dealer gamma near the price. Big positive strikes close to price raise the odds of a pin; big negative ones raise the odds of a fast move.
• Size the move. The expected move to that expiry tells you the range options are pricing.
• Know your own contracts. If you hold in-the-money stock or ETF options into the close, expect them to be exercised into shares unless you close them. Know whether an index option is AM- or PM-settled.

How to see it on Tradytics

On any options research page, such as SPY options, open interest by strike can be filtered to a single expiry and shows max pain, the bets-by-strike-and-expiry grid shows where premium is concentrated by date, and the expected move is listed by expiration. Dealer levels show the gamma by strike that expiration will remove. The AI analyst (Chat button on any page) can walk you through positioning into a date like November 20.

Common questions

What time do options expire on OPEX?

Most expiring stock, ETF and PM-settled index options stop trading at the 4:00 PM ET close on expiration day. Standard AM-settled SPX options stop the day before and settle on Friday's opening prices.

Is OPEX week bearish?

There's no reliable rule. Expiration affects how prices move around big strikes more than which way they go.

What is triple witching?

Traders' name for the quarterly expirations in March, June, September and December. The next is December 18, 2026.

Does max pain matter on OPEX?

Less than people hope. The documented effect is clustering near heavily traded strikes, and it's small next to news.

Sources

• Cboe, 2026 Options Expiration Calendar: standard expirations on November 20 and December 18, 2026; SPX weeklys every business day; end-of-month expirations.
• Cboe, Settlement of Standard, A.M.-Settled S&P 500 Index Options: the special opening quotation from Friday's opening prices.
• Cboe, S&P 500 Index Options Product Specifications: standard SPX trading ends the business day before settlement; SPXW trades until 4:00 PM ET on expiration day.
• Ni, Pearson and Poteshman, Stock Price Clustering on Option Expiration Dates (2005): closing prices cluster at strikes on expiration dates.

• SPY options traded $332.54M in premium on 2026-11-02: $193.21M in calls and $139.32M in puts, a net bullish lean of $32.03M.
• Put/call ratio 0.72.
• Options price a move of about ±$6.07 by 2026-11-02.
• Max pain for 2026-11-02 is $765.0.

Updated 2026-11-02 16:02 UTC