Stats › Options, shorts and positioning › Option expiry
Triple witching and option expiry
Four times a year, on the third Friday of March, June, September and December, stock index futures, index options and single stock options all expire in the same session. That's triple witching. The date rule has exceptions worth knowing, too: the June 2026 expiry landed on Thursday 18 June, because Juneteenth fell on the Friday and the market was shut. The coverage around these days is loud, and this page is my attempt to work out how much of it holds up.
Short version: less than you'd think. The trillion dollar figure that leads every article traces back to one analyst at one firm, and no exchange, clearing house or regulator publishes that statistic at all. The best research on what expiry does to prices measured an effect of about 0.15% net of the bid ask spread, which reversed by the next morning. And the market has changed underneath all of it, because S&P 500 options now expire every single trading day.
The mechanical part is genuinely real, to be fair. Market makers who hedged those expiring positions with the underlying shares have to unwind or roll, and most of that lands at the close. There's a naming point worth knowing as well. Quadruple witching, in the US, describes a set of instruments that no longer exists. The page covers the mechanics, the sourcing problem, what three separate academic studies actually measured, and the structural reasons expiry matters less than it once did. Where something couldn't be verified I've said so rather than filled the gap, and on this topic that happens more than once.
Triple witching is the quarterly simultaneous expiry of stock index futures, index options and single stock options on the third Friday of March, June, September and December. The headline that accompanies it, some number of trillions expiring, traces to one analyst at one firm and no exchange, clearing house or regulator publishes the statistic. The best evidence on what expiry actually does is Stoll and Whaley's finding that incremental volume is about one third of what the open interest implies, and that the price effect net of the bid ask spread was about 0.15% and reversed the next morning. The largest options day on record, over 110 million contracts on 10 October 2025, was not an expiry Friday.
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