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23 Jan 2026, 09:08 AM
Introduction of Closing Auction Session (CAS) in the equity cash segment and certain modifications in the Pre-Open auction session
SEBI will introduce a Closing Auction Session (CAS) to determine the closing price of stocks with F&O contracts. This change will come into effect from August 3, 2026.
What changes with CAS
Currently, closing prices are calculated using trades from the last 30 minutes of continuous trading system (CTS). With CAS, closing prices for eligible stocks will be determined through a dedicated auction session, similar to how opening prices are established in the pre-open session.
CAS will run as a separate 20-minute session from 3:15 PM to 3:35 PM on all trading days and will have four phases:
| Session | Particulars | Start Time | Duration |
|
1 |
Reference price calculation / Transition from CTS to CAS |
3:15 PM |
5 Mins |
|
2 |
Order entry period – for both limit and market orders |
3:20 PM | 5 Mins |
|
3 |
Order entry period only for limit orders, no modification/ cancellation for market orders, Random Close in the last 2 minutes | 3:25 PM | 5 Mins |
|
4 |
Order matching | 3:30 PM | 5 Mins |
- Order entry in the cash market will close randomly anytime between 3:28 PM and 3:30 PM. This closure is fully system-driven.
- The equity derivatives segment will continue trading till 3:40 PM on all trading days.
- The post-close session in the cash market will run from 3:50 PM to 4:00 PM, where trades are executed at the closing price.
- On special trading days, closing prices will be decided using the CAS. The derivatives segment will close 10 minutes after CAS ends, followed by a 10-minute post-close session.
Changes to the pre-open auction session
To align price discovery at the open and close, SEBI has also modified the pre-open auction session, effective September 7, 2026.
The pre-open session will continue to be 15 minutes long (9:00 AM to 9:15 AM) and will be structured as follows:
| Session | Particulars | Start Time | Duration |
|
1 |
Order entry period for both limit and market orders |
9:00 AM |
5 Mins |
|
2 |
Order entry period only for limit orders, no modification/ cancellation allowed for market orders, random close in the last 2 minutes |
9:05 AM | 5 Mins |
|
3 |
Order matching | 9:10 AM | 5 Mins |
|
4 |
Transition of orders from pre-open session to CTS | 9:12 AM | 5 Mins |
- The pre-open session will close randomly between 9:08 AM and 9:10 AM, and this closure will be system-driven.
- Only limit and market orders are allowed during the pre-open session.
Refer this circular for more details.
If you have any queries then please post them on our TradingQ&A forum here.