What it means
Derivatives are contracts whose value depends on an underlying asset such as a share or an index. Each has an expiry date, after which it either settles in cash or leads to delivery of the asset.
When several types expire together, a large amount of trading activity is packed into one session. The reason this matters is that traders and funds who hold these contracts must act before expiry.
They may close positions, roll them into later months, or settle them, and each action creates buying or selling in the underlying shares. That flow is concentrated in the final hour or so of trading, which is why prices can move unusually.
Index funds add another layer. Many index providers rebalance their indices around the same dates, so passive funds must buy and sell shares to match the new weights.
The combination can produce heavy volume in the closing auction, the short period at the end of the day when the official closing prices are set. For a non-specialist the practical lesson is to expect noise, not news.
A sharp move on the day may reflect mechanical positioning rather than a change in a company's prospects, so investors with long horizons usually avoid reacting to it. Those placing large orders may choose to trade earlier in the week to avoid the crush.
The related terms triple witching and double witching describe days when fewer contract types expire together. Exact contract availability differs by market, so the label is a convention rather than a precise legal term.
Traders sometimes talk about pinning, where a share price seems to gravitate towards a popular option strike price near expiry. Large holders of options may hedge their exposure by buying or selling the shares, and that hedging can nudge the price.
The effect is usually modest and fades once the contracts have expired.
In practice
Real-world examples.
Example
A pension fund manager needs to sell $20,000,000 of shares to meet payouts. She moves the trade to the Tuesday before the third Friday of the month, avoiding expiry-day volatility that might worsen her execution price.
Example
A day trader sees volume double in the last hour of a Friday in June and notices prices swing without any company news. He recognises the pattern as expiry-related and stays out of the market until the following week.
Example
A treasury analyst at a listed manufacturer is asked why the company's share price dropped 2% on a quiet Friday in December. She checks the calendar, sees it was a quarterly expiry day, and tells the board the move reflected trading mechanics rather than a change in the outlook. The board accepted the explanation and took no further action. She adds that a single volatile session rarely changes the long-term picture.
Case study
Seen in the real world.
Northgate Capital is an illustrative, fictional asset manager that runs an index-tracking fund. Its trading head noticed that the fund's tracking error, the gap between its return and the index, widened on certain Fridays each quarter.
The cause was that the fund had been trading its rebalancing orders at the closing auction on quadruple witching days, when volume and price swings were at their peak. Spreads were wider and prices moved against the fund by small but measurable amounts.
In the illustrative follow-up, the head of trading spread the orders across several days around the date and used limit orders, which set a maximum buying price or minimum selling price. Tracking error narrowed in later quarters, and the lesson was that knowing the calendar can save real money for large orders. The firm now publishes the dates of each expiry in its trading calendar so portfolio managers can plan around them months ahead. Within two quarters the tracking error on those dates fell to levels in line with the rest of the year.
Watch out
Common mistakes.
- Assuming a big price move on the day signals news about a company, when it is often caused by contract expiries and index rebalancing.
- Placing large market orders into the closing auction on expiry days without considering the wider spreads.
- Thinking it always means a crash, when the effect is usually higher volume and volatility in both directions rather than a fall.
Questions
People also ask.
Which contracts expire on quadruple witching?
Stock index futures, stock index options, individual stock options and single stock futures, where they are traded.
When does it happen?
Typically on the third Friday of March, June, September and December, though holidays can move the date.
Should long-term investors worry about it?
Generally not, because the effects are short-lived, but they may prefer to avoid placing large trades on those days.
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