Closing Auction Session (CAS)

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.
3:28 PM – 3:30 PM	System-driven random closure
3:30 PM – 3:35 PM	Orders are matched at a single equilibrium price, which becomes the official closing price.
3:35 PM – 3:50 PM	Transition period - CAS to Post-Close Transition
3:50 PM – 4:00 PM	Existing post-close process continues

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.

Treatment of Existing Orders at 3:15 PM

Orders Carried Forward to CAS:

•  Unexecuted Limit Orders falling within CAS price bands will be carried forward to the CAS session

•  Original order timestamps will be retained

Orders Not Carried Forward:

The following orders will not be carried forward into CAS:

•  Stop Loss (SL) Orders

•  Disclosed Quantity (DQ) Orders

•  Orders outside CAS price bands

CAS Order Entry Restrictions:

The following order types will not be permitted during the Closing Auction Session:

•  Stop Loss (SL) Orders

•  Immediate or Cancel (IOC) Orders

•  Disclosed Quantity (DQ) Orders

Market Orders:

•  Market Orders will be accepted only between 3:20 PM and 3:25 PM

•  Market Orders entered after 3:25 PM will be rejected by the Exchange

Limit Orders:

•  Limit Orders will be accepted from 3:20 PM to 3:30 PM

Order Matching:

•  All eligible orders will be matched at a single equilibrium price determined during the Closing CAS Session

•  The equilibrium price discovered during CAS will become the official Closing Price of the security.

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.

Note: Revised Trading Hours: 09:15 AM to 03:40 PM:

Additional Operational Changes

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 including F&O segment (Cover Order (CO), Bracket Order (BO), MIS Square-Off)

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

Kindly refer to the circular links below for more information on the Closing Auction Session (CAS)

• NSE FAQs on CAS: Click Here 
• NSE Circular on CAS: Click Here
• SEBI Circular on CAS: Click Here

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.