What is Triple Witching? Definition, Formula, and Example
Triple witching is the simultaneous expiration of stock index futures, stock index options, and single-stock options that occurs on the third Friday of March, June, September, and December, producing sharply elevated volume and volatility.
Plain-English Definition
Triple witching is the quarterly event when three classes of equity derivatives — stock index futures, stock index options, and single-stock options — expire on the same trading day. It falls on the third Friday of March, June, September, and December. The final hour of trading, often called the "witching hour," sees the largest concentration of volume of any session in the quarter as dealers, index funds, and arbitrageurs unwind or roll billions in notional exposure. Until 2020 the event was sometimes called "quadruple witching" because single-stock futures also expired; those contracts were delisted on OneChicago in September 2020, making triple witching the correct current term.
How It Works Mechanically
Three contract groups converge at the open or close of the third Friday:
- Stock index futures on ES, NQ, RTY, YM settle at the Special Opening Quotation on Friday morning.
- Stock index options (SPX, NDX, RUT) settle AM against the same SOQ.
- Single-stock options expire at the close on Friday afternoon.
Total notional is substantial. June 2023 triple witching expired roughly $4.2 trillion in options notional, per OCC and CBOE data — the single largest expiration in history to that point. The September 2024 expiration topped $5.1 trillion.
The mechanics that drive volatility:
1. Dealer delta unwind: market makers short gamma into expiration shed or add hedges as contracts roll off, forcing directional flow in the underlying.
2. Index rebalances: S&P and Nasdaq index changes are often timed to the same Friday, compounding the order imbalance.
3. Settlement prints: the SOQ for SPX is computed from opening prints of all 500 constituents, which creates a one-shot market-on-open order wave of several billion dollars.
Worked Example
On Friday, 2025-09-19, triple witching coincided with the quarterly S&P 500 rebalance. SPY traded 198 million shares versus a 20-day average of 62 million — over 3× normal volume. The final 15 minutes of the session alone printed 41 million shares. Realized volatility that afternoon was 28% annualized, double the preceding week's 14%. SPY's closing auction imbalance exceeded $6 billion in buy-side pressure from index rebalance flows.
Individual names with heavy options open interest — TSLA, NVDA, AAPL — showed "max pain" pinning, where the underlying closed within 0.5% of the strike with the highest aggregate short-dealer gamma. NVDA pinned at $130 into the close with $8.6 billion of notional expiring at that strike.
When Traders Use It
Institutional options desks build their quarterly calendars around the date. Volatility traders typically short vol the week before — implied vol decays faster than realized into the event — and buy it back Monday. Systematic strategies flatten exposure on Thursday to avoid being caught by a bad SOQ print. Retail traders use the session for tactical scalps on inflated volume, or simply step aside to avoid slippage that runs 2–4× normal on limit fills.
Limitations and Common Misconceptions
Triple witching does not reliably produce a directional move. Studies by CBOE and academic researchers (Chen and Williams, 2019) found the average S&P return on triple witching Fridays is statistically indistinguishable from zero — it's the intraday range that expands, not the close-to-close drift. The "witching hour" volatility also fades quickly; Monday's session usually reverts to normal liquidity. Finally, the event applies only to equity derivatives: Treasury futures, crude oil, and currency contracts expire on their own schedules and are unaffected.