India’s stock market is set for a significant operational change from August 3, 2026, as the Securities and Exchange Board of India (SEBI) rolls out the Closing Auction Session (CAS) for eligible Futures & Options (F&O) stocks. The move changes how the closing price is determined for these stocks, extends trading in equity derivatives by 10 minutes and introduces a structured auction mechanism aimed at making end-of-day prices more transparent and representative of actual market demand and supply.
While regular cash market trading hours remain unchanged for most stocks, investors trading F&O-enabled shares will have to adapt to a new closing process that replaces the existing Volume Weighted Average Price (VWAP)-based methodology. Groww, in a blog post and social media thread, explained how the new system will work and why SEBI believes it will improve price discovery.
Market timings change for F&O segment
The biggest operational change is in the final minutes of the trading session.
According to Groww, “Non-F&O stocks: No change. Regular trading till 3:30 PM.” However, stocks that are part of the F&O segment will follow a different schedule, with normal cash market trading ending at 3:15 PM, followed by the Closing Auction Session until 3:35 PM.
Meanwhile, stock and index derivatives will continue trading for an additional 10 minutes, with the market closing at 3:40 PM instead of 3:30 PM.
A post-close session in the cash market will continue from 3:50 PM to 4:00 PM, during which trades are executed at the official closing price.
Why SEBI is changing the closing price mechanism
The closing price is one of the most important reference values in India’s securities market. It is used to calculate benchmark indices such as the Nifty 50 and Sensex, determine the Net Asset Value (NAV) of mutual funds and ETFs, settle F&O contracts and value investment portfolios.
Because several market activities depend on this price, SEBI wants it to reflect genuine market consensus rather than being influenced by a handful of trades executed moments before the closing bell.
Groww notes that the Closing Auction Session is designed to improve price discovery, transparency and execution efficiency, while allowing the closing price to better represent overall buying and selling interest. The regulator also expects the common auction pool to improve liquidity for larger orders and bring Indian markets closer to global exchanges such as the NYSE and London Stock Exchange, which already use closing auctions.
How the closing price was calculated earlier
Before the introduction of CAS, the official closing price for most stocks was calculated using the Volume Weighted Average Price (VWAP) of trades executed during the last 30 minutes of the Continuous Trading Session.
As Groww explains, “The average price of a stock, with more weight given to prices at which more shares were traded.”
The brokerage illustrates the concept with a simple example. If 900 shares are traded at ₹100 and only 100 shares at ₹110, the last traded price (LTP) would be ₹110. However, the closing price would still be around ₹101 because the bulk of trading happened at ₹100. This ensured that a single late trade did not disproportionately influence the day’s official closing price.
What is the Closing Auction Session?
Instead of relying solely on VWAP, eligible F&O stocks will now undergo a dedicated auction after normal trading ends.
Groww describes it as “a short closing session where orders are matched to determine the stock’s final closing price.”
Unlike continuous trading, where matching buy and sell orders are executed immediately, CAS first collects eligible orders before matching them at a single equilibrium price. This equilibrium price is the level at which the maximum number of shares can be traded and becomes the stock’s official closing price.
The new mechanism is expected to provide a more accurate reflection of end-of-day demand and supply by considering all eligible auction orders together rather than sequentially.
How the 20-minute auction will work
The Closing Auction Session follows a structured sequence.
Trading in eligible F&O stocks will continue normally until 3:15 PM. The VWAP during this final 15-minute trading period will become the reference price for the auction. Based on this reference price, exchanges will establish a 3% price band within which auction orders can be placed. For example, if the reference price is ₹100, eligible orders can be entered between ₹97 and ₹103.
Between 3:15 PM and 3:20 PM, no fresh orders can be entered. Some pending orders will automatically shift to the auction session, while stop-loss orders, iceberg orders, disclosed quantity orders and orders outside the permitted price range will be cancelled.
From 3:20 PM to 3:25 PM, investors can place, modify or cancel both market and limit orders. However, these orders will only be collected and will not be executed immediately.
Between 3:25 PM and the random market close, only limit orders can be entered, modified or cancelled, while previously submitted market orders become locked. To discourage last-minute order flooding, the exchange will close order entry at a random time between 3:28 PM and 3:30 PM.
Finally, from 3:30 PM to 3:35 PM, all eligible buy and sell orders will be matched simultaneously. The price at which the highest quantity of shares can be traded will become the official closing price for the stock.
Which stocks are affected?
The new Closing Auction Session will initially apply only to stocks that have F&O contracts available.
Securities outside the F&O segment will continue trading until 3:30 PM, with their closing prices still determined using the existing VWAP-based methodology unless SEBI extends the framework to additional securities in the future.
For equity derivatives, trading will continue until 3:40 PM, ensuring that futures and options contracts continue to trade even after the closing auction for the underlying stocks has concluded.
Disclaimer: This story is for educational purposes only. Please consult with an investment advisor before making any investment decisions.
