India’s market regulator is changing the way expiring derivatives are settled after the country’s new closing-auction system produced the kind of price swings it was meant to avoid.

From December 7, the SEBI closing auction rules will separate the closing price used in the cash market from the price used to settle expiring futures and options. Stock derivatives will return to a volume-weighted average price based on the final 30 minutes of continuous trading, while index derivatives will use the corresponding VWAPs of their constituent stocks.

The closing auction itself is staying.

What SEBI is changing is how much influence that auction has over the much larger derivatives market.

The Closing Auction Was Introduced in August

India moved to the Closing Auction Session, or CAS, on August 3, 2026.

The basic idea was sensible.

Rather than calculating the day’s closing price only from trading during the final half-hour, buy and sell orders could be brought together in a dedicated auction to establish a single market-clearing closing price.

Many major global markets already use some form of closing auction.

The mechanism can be particularly useful for passive funds, index trackers and institutional investors that need to execute trades close to an official closing price.

The problem appeared when that cash-market price was also linked directly to settlement of derivatives contracts.

That created a much bigger consequence for any unusual move during the auction.

August 27 Exposed the Weakness

The issue became difficult to ignore on August 27.

During the auction, the Sensex’s indicative value swung by more than 2,000 points.

That did not mean the broader market had suddenly moved by that amount.

The problem was liquidity inside the auction itself.

The auction initially attracted a narrower group of orders than the regular market, even though the resulting price could influence settlement of enormous futures and options positions.

That created an awkward imbalance.

A relatively thin auction could potentially have an outsized impact on contracts whose combined value was vastly larger than the orders actually determining the closing price.

For F&O traders in India, that was the central concern.

SEBI Is Bringing Back the 30-Minute VWAP

Under the revised system, expiring stock derivatives will once again use the underlying share’s volume-weighted average price over the final 30 minutes of continuous trading.

For index derivatives, the closing settlement value will be calculated using the VWAPs of the individual index constituents during the same period.

That is important because VWAP uses many transactions across a broader time window rather than relying on one short auction.

It is therefore harder for a small number of unusual orders to shift the settlement price dramatically.

The method is also familiar.

It was the mechanism India used before the CAS rollout, meaning traders and brokers already understand how it behaves.

The derivatives settlement price will therefore be separated from the cash-market closing price from December 7.

The Cash Market Will Still Use the Auction

SEBI is not abandoning CAS.

That distinction matters.

The closing price of shares in the cash segment will still be determined through the auction.

The new session will run from 3:30 pm to 3:40 pm.

That means investors buying or selling ordinary shares can still participate in a closing-price discovery process designed to match institutional buying and selling interest.

What changes is the link between that price and expiring derivatives.

SEBI’s approach is effectively to keep the part of the reform intended to improve cash-market price discovery while removing the part that created settlement risk for derivatives traders.

Continuous Trading Will Run Until 3:30 PM

Another significant change involves market timings.

Under the earlier framework, continuous trading in stocks covered by CAS ended at 3:15 pm.

The auction then took place before the market’s final close.

From December 7, continuous cash-market trading in eligible stocks will instead continue until 3:30 pm, bringing the timing back in line with other listed securities.

The transition into the closing auction will also become much shorter.

SEBI has reduced that gap from five minutes to one minute.

The aim is to prevent liquidity from disappearing too early and reduce the disruption caused by separating ordinary trading from the closing process.

Derivative Trading Will Continue Longer

The changes affect derivatives trading hours too.

Trading in index and stock derivatives will generally continue until 3:45 pm.

There is one major exception.

Expiring index derivatives will stop trading at 3:30 pm on their expiry day.

That is when the closing auction in the cash market begins.

The structure is designed to give non-expiring derivatives more time to trade while preventing expiring contracts from being influenced by movements occurring after the settlement-reference period has ended.

It may sound like a small timing adjustment.

For high-frequency traders, brokers and institutions handling large expiry positions, a few minutes can change how positions are hedged and closed.

Why SEBI Did Not Scrap CAS Entirely

The regulator received around 20,000 responses during its review of the framework and conducted two rounds of consultation before finalising the changes.

That feedback appears to have produced a compromise rather than a reversal.

Closing auctions remain useful for institutions trying to replicate index closing levels and for funds that need to trade large portfolios at an official end-of-day price.

The concern was not really the idea of an auction.

It was using that auction to settle a derivatives market far larger and more liquid than the auction itself.

Separating the two allows India to retain closing-price discovery while reducing the incentive or possibility for short-lived auction distortions to affect expiry settlements.

Retail Investors May Notice Less Expiry-Day Noise

For an ordinary investor buying shares for the long term, the change may not transform day-to-day investing.

The bigger effect should appear around expiry sessions.

Under the previous structure, an abrupt closing-auction move could produce an unusual final settlement value for options and futures.

The revised SEBI F&O rules should make those settlement values reflect a wider period of actual continuous trading.

That does not mean expiry-day volatility disappears.

Futures and options can still move sharply as traders unwind positions.

The change simply reduces the chance that one unusually thin closing auction determines the final outcome.

December 7 Is the Date Traders Need to Remember

SEBI’s revised framework takes effect on December 7, 2026.

Until then, traders will continue operating under the current structure.

After the change, two different closing concepts will matter.

The cash-market closing price will come from the 3:30 pm to 3:40 pm auction.

The settlement of expiring stock and index derivatives will rely on the final 30-minute VWAP from continuous trading.

It is a more complicated arrangement than using one price for everything.

But after the volatility seen following the August rollout, SEBI appears to have decided that separating those functions is safer.

The Closing Auction Session stays.

Its power over derivatives expiry does not.

Source:

NDTV: SEBI Tweaks Expiry Rules After Market Chaos: What Changes From December 7