The "expiry day" is the day set for the expiration of derivative contracts such as futures and options. In India, for monthly contracts, this falls on the last Thursday of the month. Open derivative contracts are settled, either physically or in cash, and new contracts for the following month open for trading. The day is associated with unusually high trading activity due to liquidity, volatility and sharp price moves, which in turn draws investors toward high-risk, high-reward strategies such as straddles and hedging positions timed to rapidly shifting conditions.
What Happened with Jane Street?
Jane Street is a global quantitative trading firm known for its sophisticated arbitrage strategies. On 27 June 2024, the monthly expiry day for index derivatives, Jane Street allegedly executed trades that capitalised on a pricing inefficiency in the Nifty and Bank Nifty contracts during the last thirty minutes of trade, right before expiry. Market speculation suggested that the firm made substantial profits from a mismatch between the spot and futures prices of these indices, potentially at the expense of passive index funds and retail traders. This raised concerns that expiry day had become vulnerable to manipulation by institutional traders using ultra-fast algorithmic trades, and SEBI launched a review into expiry day mechanics that soon translated into regulatory change.
What Changed, and Why
Prior to SEBI's intervention, India's derivative contracts for Nifty, Bank Nifty and other indices expired on the last Thursday of the month, or the preceding business day if that Thursday was a holiday, with the settlement price based on the volume-weighted average price of the underlying index over the last half-hour of trading. That meant settlement depended on an average price over a specific window rather than the closing price itself, a structure that was vulnerable to concentrated buying or selling within that window, particularly in illiquid contracts or thin market conditions.
In response, SEBI mandated the following changes:
- A new settlement mechanism: moving expiry settlement away from the last thirty minutes' volume-weighted average price toward a single closing price based on the cash market's close, in line with global best practice;
- Randomisation of the closing window: a system that randomises the precise timing of closing price capture, making it harder for any trader to time large trades at a specific moment at expiry; and
- Tighter surveillance and disclosure: exchanges were instructed to put real-time surveillance on expiry day trades in place, and to release anonymised expiry-day trade data to improve transparency.
The underlying logic was to reduce volatility, avoid price distortion and shield retail and passive investors from being drawn into aggressive expiry-day strategies.
What It Means for Market Participants
No formal charges have been brought against Jane Street or other participants over the June 2024 trades, but SEBI's proactive response signals that algorithmic and high-frequency trades during expiry windows are under deeper scrutiny, and that disruptive trading behaviour, even where technically legal, could attract future enforcement or policy action under SEBI's Prohibition of Fraudulent and Unfair Trade Practices regulations. Brokers and institutions should expect stricter compliance expectations around proprietary expiry-day strategies, alongside a broader shift toward a "substance over form" approach, where SEBI may act even absent a clear breach of black-letter law if a transaction runs contrary to the general principle of market fairness.
For retail and position traders, tying the expiry price to the wider market close rather than a narrower, more easily influenced average should mean fewer price spikes driven by large players, and less exposure to sudden expiry-day swings. For option writers and expiry-focused strategies, the new settlement environment is likely to require a reset of existing approaches, since it narrows the scope for large intraday moves on expiry itself. Institutional players relying on arbitrage may see reduced scope for outsized expiry-day profit, offset by a market that is, on balance, deeper and more stable.
Disclaimer: The content of this article is intended to provide general guidance on the subject matter. Specialist advice should be sought about your specific circumstances.