[Updated on 01/JUL/26]
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FAQs on Pre-open Session in Equity (CM) Segment
Version 1.0
July 2026
(this FAQ shall be applicable w.e.f. September 07,2026)
Disclaimer:
“This document/FAQ summarizes the queries relating to the above topic(s) in a concise
manner for the Member’s ease of understanding. The information and/ or content (collectively
‘Information’) provided herein is general information only and NSE has issued detailed
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that the Information is adequate and reliable, no representation is made by NSE as to its
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liability of whatsoever nature for any direct/indirect or consequential loss, including without
limitation any loss of profits, arising from reliance on this Information. In the event of any
difference/ inconsistencies between the Information as provided herein and in the circulars,
the Information in the circulars shall be construed as final and binding. NSE does not in any
way control, warrant or provide guarantee on the suitability of the Information for the readers’
usage. The readers are expected to undertake their own diligence and are advised not to solely
rely on this document. Any such reliance shall be at the reader’s own risk. Nothing stated
herein shall bind NSE, in any manner whatsoever.”
[Updated on 01/JUL/26]
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1. For which securities pre-open are applicable in equity market?
The pre-open session with call auction mechanism is applicable to all equity market securities
including SME securities, partly paid-up securities, and InvITs/REITs.
2. What are the session timings?
The pre-open session shall be conducted using call auction mechanism for duration of 15
minutes i.e., from 9:00 am to 9:15 am. The pre-open schedule shall be as follows:
Session
Current Time
Revised Time
Remark
Order Entry
Period
9:00 am -
9:08 am (*)
9:00 am - 9:05 am
•
Order
entry,
Modification
and
Cancellation for both limit and market
orders.
-
9:05 am - 9:10 am (*)
•
Order entry, order modification, order
cancellation period only for limit
orders.
•
No modification/ cancellation allowed
for market orders
•
(*) system driven random closure in
the last 2 minutes
Order
Matching &
trade
Confirmation
Period
9:08 am (*) –
9:12 am
9:10 am (*) – 9:12
am
•
(*) Order matching period will start
immediately after completion of order
entry period.
•
Opening price determination.
•
Order
matching
and
trade
confirmation.
Buffer
Period
9:12 am -
9:15 am
9:12 am - 9:15 am
(no change)
•
Transition
from
pre-open
to
Continuous Trading Session (CTS)
Note: In case of index-based market-wide circuit filter breach or any outage (stopping of trading, either
suo moto by Exchange or by the virtue of reasons beyond control of stock exchange), the market shall
open with a pre-open session, and its timings shall be informed separately on that day.
3. What shall be the trading parameters for pre-open session?
The below shall be the parameters applicable for pre-open session:
Particulars
Equity Market
SME Securities (Series
SM/ST/SZ)
Market
“N”
“N”
Lot Size
Same as Normal Market
Applicable Lot size
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Tick Size
Same as Normal Market
Same as Normal Market
Price Band
Same as Normal Market
Same as Normal Market
Book type
PO
PO
4. What shall be the indicator for identifying securities in pre-open and normal markets
across specified files?
The below shall be the indicator for identifying securities in pre-open and normal market across
the specified files:
5. How many sessions do Pre-open session comprise??
Pre-open session comprises of two sessions as mentioned below:
1. Order Collection Period
2. Order Matching Period
6. What are the features of order collection period in pre-open session?
•
During this period orders can be entered, modified, and cancelled.
•
Order collection period ends by system driven random closure in the last 2 minutes.
•
Both Limit and market order are allowed as per applicable window timings provided in
question number 2 above.
•
The information like Indicative equilibrium / opening price of scrip, total buy and sell quantity
of the scrip, Indicative NIFTY 50 Index value & % change of indicative equilibrium price to
previous close price shall be computed based on the orders in order book and are
disseminated
during
pre-open
session.
[Updated on 01/JUL/26]
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Special term orders like Stop loss (SL), Immediate or Cancel (IOC) and Disclosed Quantity
(DQ) shall not be allowed.
•
Algo market orders shall be allowed during initial 5 mins of order entry period when both limit
and market orders are allowed.
•
When market orders are restricted, any market order placed shall be rejected by the Exchange
with an appropriate error message on NEAT – “Market orders are currently not allowed.”
•
The information like Indicative equilibrium / opening price of security, total buy and sell
quantity of the security and % change of indicative equilibrium price to previous close price
shall be computed based on the orders in order book and will be disseminated during pre-
open session.
7. What are the features of order matching period in pre-open session?
•
Order matching period starts immediately after completion of order collection period.
•
Order will be matched at a single (equilibrium) price which will be open price.
•
Market orders shall be given priority over limit orders. The sequence for order matching shall
be as under:
➢ Eligible market orders shall be matched with eligible market orders in the order
of time priority at the equilibrium price.
➢ Residual eligible market orders, in the order of time priority, shall be matched with
limit orders in the order of price-time priority.
➢ Remaining limit orders shall be matched with limit orders in the order of price-
time priority.
•
During order matching period order modification, order cancellation, trade modification and
trade cancellation are not allowed.
•
The trade details are disseminated to respective members before the start of normal
market.
8. On what basis is the equilibrium / opening price determined for pre-open session?
•
The opening price is determined based on the principle of demand supply mechanism.
•
The equilibrium price is the price at which the maximum volume is executable.
•
In case more than one price meets the said criteria, the equilibrium price is the price
at which there is minimum order imbalance quantity (unmatched order quantity). The
absolute value of the minimum order imbalance quantity is taken into consideration.
•
In case more than one price has same minimum order imbalance quantity, the
equilibrium price is the price closest to the previous day’s closing price. In case the
previous day’s closing price is the mid-value of pair of prices which are closest to it,
then the previous day’s closing price itself is taken as the equilibrium price. In case of
corporate action, previous day’s closing price is adjustable closing price or the base
price.
•
Both limit and market orders reckon for computation of equilibrium price.
•
The equilibrium price determined in pre-open session is considered as open price for
the day.
•
In case of only market orders exist both in the buy and sell side, then order is matched
at previous day’s close price or adjusted close price / base price. Previous day’s close
or adjusted close price / base price is the opening price.
•
In case of no price is discovered in pre-open session, the price of first trade in the
normal market is the open price.
[Updated on 01/JUL/26]
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9. What happens to unmatched orders which are entered in the pre-open session?
•
All unmatched / outstanding limit orders will be moved to the normal market retaining
the original time stamp. All unmatched / outstanding market orders will be modified
to assign discovered equilibrium price and moved to normal market as limit orders
with such modified time stamp.
•
In a situation where no equilibrium price is discovered in the pre-open session, all
market orders are moved to normal market at base price
•
Order modification and/or cancellation of all unmatched / outstanding orders shall not
be permitted before start of normal market session
10. Will the orders received during the pre-open session be validated against the applicable
margins?
All orders received in pre-open session shall be validated at the applicable margins for
sufficiency of available capital prior to acceptance of the orders. If the available capital of the
member is insufficient to cover the margin requirement of the order placed, the same shall
not be accepted for the pre-open session.
11. Pre-open session data will form part of which trading files?
•
The relevant pre-open data shall form a part of trade file, security file, MII security file,
bhavcopy files which are disseminated by the Exchange.
•
The indicator to identify securities eligible for pre-open and normal market sessions is
referenced in question number 2 of this document.
12. Does the information related to pre-open shall be disseminated to websites?
Yes. Information with respect to Indicative Equilibrium Price, Indicative Equilibrium
Quantity of pre-open session shall be disseminated on website.
13. Will Cancel on Logout (COL) , Kill Switch (Trading member level and User level) feature be
applicable in pre-open session in equity derivatives segment?
No. Cancel on Logout (COL), Kill Switch (Trading member level and User level) facility shall
not be applicable for orders entered in pre-open session in equity segment.
14. Will the Self Trade Prevention Check (STPC) mechanism be applicable during the pre-
open session in the equity segment?
Yes, the Self Trade Prevention Check (STPC) mechanism will be applicable during the pre-
open session in the equity segment
The STPC mechanism will be active during the order entry/collection period of the pre-open
session. If a potential self-trade is detected, the active order will be cancelled by default,
regardless of the STPC option set in the order.
[Updated on 01/JUL/26]
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15. What are the Pre-Trade Risk Controls applicable for Market Price Protection (MPPto
securities eligible for the pre-open session?
The details for Market Price Protection (MPP) are provided in Exchange consolidate circular
reference no. NSE/CMTR/73927 dated April 28,2026.
16. Which error message is displayed on the TWS when a trade cancellation request is made
for a trade executed during the pre-open?
When a trade cancellation request is made on TWS for a pre-open trade, the system will not
allow the cancellation. Instead, the following error message will be displayed:
"Trade executed during pre-open session not allowed to cancel"
17. What are the different error messages proposed to be displayed on the NEAT Terminal for
order rejections encountered during the Pre-Open Session or prior to the commencement
of the normal market?
The details of error code messages is available in the protocol document which is available in
the below link:
https://www.nseindia.com/static/trade/platform-services-neat-trading-system-protocols
18. What type of information shall be disseminated pertaining to the pre-open session in
TWS?
The following information shall be disseminated pertaining to the pre-open session:
Information
NEAT Trading Terminal
Indicative equilibrium price of stocks
Yes
Indicative tradable quantity of stocks at
indicative equilibrium price
Yes
Indicative cumulative buy and sell
quantity of stocks i.e. total buy & total
sell order quantities
Yes
(as currently disseminated in MBP)
Indicative imbalance quantity of stock
at equilibrium price
Yes
Indicative imbalance quantity based on
market orders of stock i.e. difference
between outstanding total buy & sell
market order quantities.
Yes
19. What message shall be broadcasted on NEAT terminals?
Below are messages that shall be broadcasted on NEAT terminal for pre-open session:
Particular
Message
At start of pre-open session
The Normal market has pre-opened for DD MMM
YYYY
[Updated on 01/JUL/26]
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When market order
restrictions during order
entry period starts
Market orders are now restricted during pre-open
session.
At end of the pre-open
session
The PREOPEN period has ended. Please wait for
securities to be opened for trading.
20. What will happen in the event of Index – NIFTY 50 breaches its prescribed threshold
limit?
In the event NIFTY 50 breaches its prescribed threshold limit upon calculation of the opening
value of NIFTY 50 at the closure of pre-open session, a trading halt will be triggered as per
SEBI Circular Ref. No. CIR/MRD/DP/25/2013 dated September 03, 2013, on index-based
market-wide circuit breaker system.
The trading halt shall be applicable at the start of the continuous trading session. The index
breach will not impact the execution and confirmation of trades during the pre-open matching
session.
*********************************END*****************************
National Stock Exchange of India Limited
Circular
Department: CAPITAL MARKET SEGMENT
Download Ref No: NSE/CMTR/74969
Date: July 01, 2026
Circular Ref. No: 91/2026
All Members,
Modifications in the Pre-Open Call Auction framework
This is with reference to SEBI circular reference HO/47/11/11(3)2025-MRD-POD2/I/2765/2026 dated
January 16, 2026 regarding Introduction of Closing Auction Session (CAS) in the Equity Cash Segment and
certain modifications in the Pre-Open Auction Session, and in partial modification to Chapter 1.1 Pre-open
session (Regular) in Capital Market Consolidated Circular reference 73927 dated April 28,2026.
As per the aforesaid SEBI circular, the framework of existing pre-open session shall be aligned with the
CAS framework and the following modifications will be implemented in the Pre-Open Session:
A. Session Timings
The pre-open session shall be for a period of 15 minutes i.e. from 9:00 am to 9:15 am. The changes in pre-
open session comprising of Order entry period, order matching period and buffer period are provided in
below table:
TABLE A
Session
Current Time
Revised Time
Remark
Order Entry
Period
9:00 am -
9:08 am (*)
9:00 am - 9:05 am
•
Order
entry,
Modification
and
Cancellation for both limit and market
orders.
-
9:05 am - 9:10 am (*)
•
Order entry, order modification, order
cancellation period only for limit
orders.
•
No modification/ cancellation allowed
for market orders
National Stock Exchange of India Limited
Page 2 of 4
(*) system driven random closure in the
last 2 minutes
Order
Matching &
trade
Confirmation
Period
9:08 am (*) –
9:12 am
9:10 am (*) – 9:12
am
•
(*) Order matching period will start
immediately after completion of order
entry period.
•
Opening price determination.
•
Order
matching
and
trade
confirmation.
Buffer
Period
9:12 am -
9:15 am
9:12 am - 9:15 am
(no change)
•
Transition
from
pre-open
to
Continuous Trading Session (CTS)
Note: In case of index-based market-wide circuit filter breach or any outage (stopping of trading, either suo
moto by Exchange or by the virtue of reasons beyond control of stock exchange),the market shall open with
a pre-open session and its timings shall be informed separately on that day.
Additional Notes:
1.
Order Entry Period:
a) Special term orders like Stop loss (SL), Immediate or Cancel (IOC) and Disclosed Quantity (DQ)
shall not be allowed.
b) Algo market orders shall be allowed during initial 5 mins of order entry period when both limit
and market orders are allowed.
c) When market orders are restricted, any market order placed shall be rejected by the Exchange
with an appropriate error message on NEAT – “Market orders are currently not allowed.”
2.
Trade Cancellation:
Request for trade cancellation shall not be allowed for trade executed in pre-open. Such a request
shall be rejected by the system with appropriate error message.
Error message on NEAT: Trade executed during pre-open is not allowed to cancel.
B. Order matching priority during pre-open session:
Market orders shall be given priority over limit orders. The sequence for order execution matching shall
be as under:
a) Eligible market orders shall be matched with eligible market orders in the order of time priority
at the equilibrium price.
b) Residual eligible market orders, in the order of time priority, shall be matched with limit orders
in the order of price-time priority.
c) Remaining limit orders shall be matched with limit orders in the order of price-time priority.
National Stock Exchange of India Limited
Page 3 of 4
C. Data Dissemination
Summary of the information to be disseminated during pre-open session is provided below:
Information
NEAT Trading Terminal
Indicative equilibrium price of stocks
Yes
Indicative tradable quantity of stocks at indicative
equilibrium price
Yes
Indicative cumulative buy and sell quantity of
stocks i.e. total buy & total sell order quantities
Yes
(as currently disseminated in MBP)
Indicative
imbalance
quantity
of
stock
at
equilibrium price
Yes
Indicative imbalance quantity based on market
orders of stock i.e. difference between outstanding
total buy & sell market order quantities.
Yes
Indicative open price of all the indices including
NIFTY50
Yes
D. Message broadcasted on NEAT terminals
Below messages shall be broadcasted on NEAT trading terminal for pre-open session:
Event
Message
At start of Pre-Open session
The Normal market has pre-opened for DD
MMM YYYY
When market order restrictions during order
entry period starts
Market orders are now restricted during pre-
open session.
At end of the Pre-Open session
The PREOPEN period has ended. Please wait
for securities to be opened for trading.
E. All other features/functionalities as mentioned in Chapter 1.1 Pre-open session (Regular) section
of consolidated circular 73927 dated April 28, 2026 remain unchanged
Members are requested to note that the above changes in pre-open session shall be effective from
September 07, 2026. Further, the functional changes resulting from the implementation of the above shall
be available for testing in mock trading sessions. Exchange shall issue separate circular w.r.t these mock
trading sessions.
Also, members are advised to load the updated security.gz and NSE_CM_security_ddmmyyyy.csv.gz file in
the trading application before trading from the effective date. This file can be obtained from the directory
cmftp/common/ntneat on the Extranet server. Additionally, members can access the MII contract file -
NSE_CM_security_ddmmyyyy.csv.gz on the website path :- https://www.nseindia.com/all-reports.
National Stock Exchange of India Limited
Page 4 of 4
The updated FAQs related to Preopen session in Equity segment is attached as Annexure .
Members may also access the latest version of the FAQs on the NSE website using the link provided below:
https://www.nseindia.com/static/trade/continuous-markets-FAQs
For and on behalf of
National Stock Exchange of India Limited
Khushal Shah
Associate Vice President
Toll Free No
Email id
1800-266-0050 (Option 1)
msm@nse.co.in
