Narration: AI voice.
Everything expires at once
Friday, September eighteenth, 2026. Triple witching. Cboe's definition: the simultaneous expiration of individual stock options, equity index options and equity index futures, four times a year. Cboe adds there is often an observed increase in trading volume and market volatility. So what does this one's record actually show?
The record
The session record. SPX closed at 7,650.50, up 0.17%. High to low, 46.65 points. The morning read: no gamma side called. The page says the two estimators of dealer positioning disagree near the flip. Flip at 7,617.59: touched. Call wall untouched, closest approach 142.83 points. Put wall untouched, 110.52.
The other number that day
Same session, a second number. The dark pool index, DIX, read 52.4%, the high of the page's 260-session window. Median, 45.4%. DIX is the dollar-weighted share of off-exchange volume in S&P 500 stocks that FINRA reports as short sales. Most of it is market makers filling customer purchases. It describes where volume traded, not who was buying. Not a signal.
Wrap
Two dated facts, one session, side by side. Nothing here says one caused the other. Not a forecast. What settles on a witching day, and when, is on the learn page linked below. Educational only.
Full write-up with sources: /learn/triple-witching-explained
Educational content, not investment advice.
Levels shown are as captured on 2026-10-16 01:55 ET; they are not current.