Four times a year, stock index futures, stock index options and equity options all expire on the same morning. That overlap is triple witching, and it lands on the third Friday of March, June, September and December. The rest of the time, traders use "OPEX" as shorthand for the monthly third-Friday expiration, when the bulk of listed open interest comes off the board at once. Neither event changes what your contracts are worth, but both change the market you're trading them in: volume spikes, dealer hedging flows get mechanical, and price can behave in ways that have nothing to do with the news.
If you trade short-dated contracts, this matters more than it does for anyone else. A quarterly expiration Friday is a 0DTE session with a crowd in it.
What triple witching actually is
Three contract families settle together:
- Stock index futures (the quarterly S&P 500, Nasdaq-100 and Russell contracts)
- Stock index options
- Options on individual stocks and ETFs
You'll still see the term "quadruple witching," which came from an era when single-stock futures also traded in the US. They were delisted, so three is the accurate count.
The important part isn't the vocabulary. It's that the quarterly expiration carries far more open interest than a normal month. Institutional hedges, covered calls, collars, LEAPS and index overlays are typically written to the quarterly cycle, so March, June, September and December expirations accumulate positions all year. When those positions settle, somebody has to roll them, close them, or let them go — and the underlying shares or futures used to hedge them get bought or sold in the process.
Quarterly index rebalances often land on the same day. The S&P indices reconstitute at the close on that third Friday, which is why the closing auction on a triple witching session is routinely one of the heaviest of the year.
OPEX vs triple witching
OPEX is the broader term. Every month has a standard expiration on the third Friday, and in today's market most large-cap names and index products also have weekly expirations — several a week in SPX, SPY and QQQ. When a trader says "it's OPEX week," they almost always mean the monthly cycle, not Tuesday's weekly.
Monthly OPEX | Triple witching | |
|---|---|---|
When | Third Friday, every month | Third Friday of March, June, September, December |
What expires | Monthly stock, ETF and index options | Monthlies plus index futures and futures options |
Open interest | Large | Largest of the quarter |
Index rebalance | Occasionally | Usually |
Closing auction | Heavy | Heaviest sessions of the year |
So every triple witching day is an OPEX day; most OPEX days aren't triple witching.
Why expiration day moves differently
Gamma concentration
As contracts approach expiration, delta turns into a switch rather than a slope. An at-the-money NVDA call that expires in hours can run from 0.40 delta to 0.95 on a 1% move, and the market makers short that call have to buy shares to stay hedged. That hedging is what makes expiration-day moves feel self-reinforcing in one direction, then abruptly stall. The mechanics live in gamma and its cousins charm and vanna, and the options Greeks guide covers how those values behave as time to expiration collapses.
Pinning
Heavy open interest at a round strike can act like a magnet into the afternoon. Dealers hedging a large block of strikes sell into strength and buy into weakness around that level, which dampens movement. It isn't a rule, and it fails constantly in trending markets, but a stock drifting sideways within pennies of a big strike at 3:00 p.m. on expiration Friday isn't a coincidence.
The unwind
Rolls dominate the tape. A fund that's long December index puts and wants the hedge in March has to sell one and buy the other, and the futures leg gets adjusted alongside. That flow is price-insensitive — it happens because the calendar says so. It's one reason expiration-day direction in the morning often has little predictive value for the following week.
Settlement: the detail that catches people out
Standard third-Friday index options on the S&P 500 are A.M. settled. They stop trading at Thursday's close, and their settlement value is calculated from Friday's opening prints in each component stock — published by Cboe as SET on its index settlement values page. Because the components don't all open at the same instant, that number can differ noticeably from any price the index actually traded at.
The weekly and end-of-day contracts (SPXW) are P.M. settled and trade until the close like equity options do. Practically, on a triple witching Friday the SPX contract you'd trade intraday is the P.M.-settled weekly, not the quarterly that already stopped trading. Equity and ETF options — AAPL, META, COIN, SPY — are physically settled and trade through 4:00 p.m. ET, with in-the-money contracts subject to automatic exercise.
Knowing which one you're holding is the difference between a clean exit and an unexpected stock position on Monday morning.
How to trade an OPEX session
A quarterly expiration isn't an edge by itself. What it offers is a change in conditions you can either use or avoid on purpose.
Expect a different open. Spreads widen on the opening rotation while settlement prints are being calculated, and the first ten minutes can produce a move that completely reverses. Sizing down early is cheaper than being right an hour later.
Respect liquidity in the names, not the headline. SPX, SPY and QQQ stay tight all day. A thinly traded far-dated strike in a mid-cap does not, and expiration flow doesn't help you get filled.
Watch what volatility does after the event. Hedges that expire are often not replaced immediately, and index implied volatility can bleed in the sessions that follow. If you're buying premium into an expiry, you're paying for an event the whole market has on its calendar.
Decide in advance whether you're holding to the bell. Long contracts expiring that day go to zero if they finish out of the money. Short ones carry assignment risk. The structure you choose should match that reality, and the options strategies guide breaks down which setups are built to be held into expiration and which aren't.
Have a flat time. Traders on Vanquish plans have one built in: every position closes by 3:59 p.m. ET, which means no exercise, no assignment and no Monday surprise from a strike that finished a penny in the money.
Where this intersects with 0DTE
Expiration Friday is the original zero-days session, and the same mechanics that drive a 0DTE options trade on a Tuesday show up magnified four times a year: brutal theta, delta that behaves like a light switch, and a late-day tape driven by hedging rather than opinion. The difference is scale. On a quarterly expiration, the hedging flow comes from positions built over months, not days, and the closing auction can absorb it in a single print.
If you trade short-dated contracts regularly, our 0DTE coverage and the wider options education library go deeper on managing those sessions — including why the last thirty minutes of an expiration Friday rewards a plan more than a prediction.
FAQs
Is triple witching bullish or bearish?
Neither. The flow is mechanical: rolls, hedges and index rebalances that happen because of the calendar. Studies of expiration-day returns don't produce a reliable directional bias, and intraday direction frequently reverses. Volume and range tend to be elevated; direction is not predictable from the event itself.
What time does triple witching affect the market most?
The opening rotation and the closing auction. Index settlement values are set from the opening prints, and the index rebalance plus most unwinds execute on the close. The middle of the day often trades quietly by comparison.
Can I hold an option through triple witching expiration?
You can, but know how it settles. Cash-settled index contracts settle to a calculated value; equity and ETF options are physically settled and exercised automatically if they finish in the money by a cent. If you don't want the shares, close the position before the bell.
Does OPEX happen every month?
Yes. Standard monthly contracts expire on the third Friday of every month. Triple witching is the quarterly version, in March, June, September and December, when index futures expire alongside them.
How does triple witching affect single stocks?
Names with heavy concentrated open interest — large caps like TSLA and AMZN, or high-volume crypto-linked stocks like MSTR — can see pinning near big strikes and a volume surge at the close. Smaller names with thin option interest usually trade a normal day.
Triple witching gets talked about as if it were a market event in its own right. It's closer to a plumbing event: four times a year, a quarter's worth of hedges and index positions have to be settled or rolled, and the tape reflects that. Treat it as a day with different liquidity and different late-session behavior, size accordingly, and know how everything you're holding settles.
If you want to trade those sessions without putting your own money at risk, our options trading plans run on live market data in simulation, with payouts based on what you produce.
