Closing Auction Session (CAS)

The stock exchanges are introducing the Closing Auction Session (CAS) for F&O-eligible stocks, effective 3 August 2026, with the objective of enhancing the accuracy, transparency, and integrity of the official closing price.

This new market framework also brings changes to derivatives trading hours and certain trading timelines. Whether you're an investor or an active trader, understanding these changes will help you trade more effectively.

What is the Closing Auction Session (CAS)?

The Closing Auction Session (CAS) is the final phase of the trading day where buy and sell orders are matched through an auction mechanism to determine the official closing price of a security.

Unlike the regular trading session, where orders are executed continuously throughout the day, the Closing Auction Session matches all eligible orders at a single equilibrium price based on the highest executable trading volume.

How Does the Closing Auction Session Work?

The Closing Auction Session follows a structured sequence of events.

Time	Activity
9:15 AM – 3:15 PM	Regular trading in F&O-eligible cash market stocks
3:15 PM – 3:20 PM	Continuous trading ends. Eligible orders are carried forward to the auction. Certain orders such as stop-loss and out-of-band limit orders are cancelled. No fresh orders are accepted during this period.
3:20 PM – 3:25 PM	Investors can place or modify Market and Limit Orders. The exchange publishes the indicative closing price along with order imbalance information.
3:25 PM – 3:30 PM	Only Limit Orders are accepted. Market Orders are frozen. A random auction end between 3:28 PM and 3:30 PM helps prevent last-minute price manipulation.
3:30 PM – 3:35 PM	Orders are matched at a single equilibrium price, which becomes the official closing price.

Important: Only F&O-eligible stocks will stop continuous trading at 3:15 PM. Trading in non-F&O stocks will continue until 3:30 PM as usual.

Changes in the Derivatives (F&O) Market

To enable traders to manage their positions after the official closing price is determined, the exchanges are extending derivatives trading hours.

Key Changes

• Equity derivatives trading will now continue until 3:40 PM.
• Traders can hedge or adjust Futures & Options positions based on the auction-determined closing price of the underlying stock.
• This provides greater flexibility for risk management and position adjustments.

Changes in Intraday Square-Off Timings

As part of the revised market framework, intraday square-off timings for the Cash Segment will also change.

Order Type	Current Timing	Revised Timing
MIS Square-Off	3:15 PM	3:05 PM
Bracket Order (BO)	3:10 PM	3:00 PM
Cover Order (CO)	3:10 PM	3:00 PM

Note: There are no changes to intraday square-off timings for other trading segments.

Changes in After Market Order (AMO) Timings

The timing for placing After Market Orders (AMOs) has also been revised.

Segment	Current Timing	Revised Timing
Cash Segment	3:30 PM	4:01 PM
Futures Segment	3:42 PM	4:01 PM

Benefits of the Closing Auction Session :-

The introduction of CAS offers several advantages for market participants.

• Improved Price Discovery

The auction mechanism aggregates buy and sell orders to arrive at a fair and efficient closing price.

• Reduced Price Manipulation

The random auction end and single-price execution reduce the chances of influencing the closing price through last-minute trades.

• Greater Market Transparency

The publication of the indicative closing price and order imbalance provides participants with better visibility before order matching.

• Better Benchmark Pricing

The official closing price becomes a more reliable benchmark for valuations, settlements, and institutional transactions.

• Enhanced Risk Management

Extended F&O trading hours allow traders to hedge positions after the underlying stock's final closing price is determined.

FAQs

Q1. What is the Closing Auction Session?

It is a special auction-based trading session conducted after regular market hours to determine the official closing price of eligible securities.

Q2. Why is CAS important?

CAS improves price discovery, enhances transparency, reduces price manipulation, and strengthens market integrity.

Q3. Can retail investors participate?

Yes. Retail investors can participate through their stock broker, subject to exchange rules and platform eligibility.

Q4. Will all orders be executed?

No. Orders are executed only if they are successfully matched at the auction-determined equilibrium price.

Q5. Will the closing price always match the last traded price?

Not necessarily. The official closing price determined during CAS may differ from the last traded price recorded during regular market hours.