[Updated on: 01/JUL/26]
Toll Free Number 1800 266 0050 [IVR – 1] or Email: msm@nse.co.in
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FAQ on Pre-open Session in Equity Derivatives (F&O)
Segment
Version 2.0
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
circulars to such effect from time to time. While reasonable care has been exercised to ensure
that the Information is adequate and reliable, no representation is made by NSE as to its
accuracy, correctness or completeness and NSE, its affiliates and subsidiaries accepts no
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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Page 2 of 8
1. For which instruments pre-open is applicable in equity derivatives market?
Pre-open session is applicable for both single stocks and indices futures in equity derivatives
market.
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,
Modification
and
Cancellation for limit orders only
•
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 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 are the eligible contracts on which pre-open shall be applicable?
The pre-open shall be applicable for current months futures contracts only on both single stocks
and indices. However, in the last five trading days before the current month expiry, this session
shall be extended to next-month futures contracts.
[Updated on: 01/JUL/26]
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Page 3 of 8
Illustration to the above is given herewith:
Assume, current month (M1) expiry is 30DEC2025 and next month (M2) expiry is 27JAN2026,
then following shall be applicability of pre-open session:
Trading Date
M1 - Expiry 30DEC2025
M2 - Expiry 27JAN2026
Applicability of Pre-Open Session
01-DEC-2025 to 21-DEC-
2025
Yes
No
22-DEC-25
Yes
No
23-DEC-25
Yes
Yes
24-DEC-25
Yes
Yes
25-DEC-25
Holiday
Holiday
26-DEC-25
Yes
Yes
27-DEC-25
Holiday
Holiday
28-DEC-25
Holiday
Holiday
29-DEC-25
Yes
Yes
30-DEC-2025 - Expiry Day
Yes
Yes
Trading Date
M1 - Expiry 27JAN2026
M2 - Expiry 24FEB2026
Applicability of Pre-Open Session
31-DEC-25
Yes
No
Note: Since Pre-open will not be applicable for Far month (M3) expiry contracts, above
illustration does not cover reference to the same.
4. What shall be the indicator for identifying contracts in pre-open and normal markets
across specified files?
The below shall be the indicator for identifying contracts in pre-open and normal market across
the specified files:
Report
Name
File
nomenclature
File Path
Field
Numb
er
Field
name
Values to be
provided
ISO
Tags
Structure
of
contract.t
xt
contract.txt
Extranet Path-
/faoftp/faocomm
on ;
/common/ntneat
Website Path-
https://www.nsei
ndia.com/all-
reports-
derivatives
15
Trading
status(Nor
mal mkt)
Value will be
1 = STOCK_PRE-
OPEN
2 = STOCK_OPEN
(Normal market
identifier)
3 =
STOCK_SUSPEND
ED
4 = STOCK_PRE-
OPEN_EXTENDED
6 = PRICE
DISCOVERY (Pre-
open market
identifier)
-
Structure
of MII -
contract
master
file
NSE_FO_contract
_ddmmyyyy.csv.g
z
32
TradgSts
NrmlMkt
[Updated on: 01/JUL/26]
Toll Free Number 1800 266 0050 [IVR – 1] or Email: msm@nse.co.in
Page 4 of 8
5. In what scenarios pre-open shall not be applicable?
Pre-open shall not be applicable in following scenarios:
1. Spread & Option contracts on Indices and stocks.
2. Pre-open session shall not be conducted in Futures of underlying security on its ex-
date of corporate action due to scheme of arrangement.
6. What shall be the trading parameters for Equity Derivatives market for pre-open session?
The below shall be the parameters applicable for pre-open session:
Market
Lot Size
Tick Size
Price Band
Book type
“N”
Same as
Normal Market
Same as
Normal Market
Same as
Normal Market
PO
7. How many sessions do Pre-open session comprise?
Pre-open session comprises of two sessions as mentioned below:
1. Order Entry Period
2. Order Matching & trade Confirmation Period
8. 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.
•
Algo market orders shall be allowed during initial 5 mins of order entry period when both
limit and market orders are allowed.
•
During Order entry period 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 contract, total buy and sell
quantity of the contract 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.
9. 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:
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.
[Updated on: 01/JUL/26]
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Page 5 of 8
•
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. Request for trade cancellation shall not be allowed for these trades.
10. 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 base price. Therefore, 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.
11. 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
12. Will the orders received in pre-open session be validated at 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.
13. Pre-open session data will form part of which trading files?
•
The relevant pre-open data shall form a part of trade file, contract file, bhavcopy files
which are disseminated by the Exchange.
[Updated on: 01/JUL/26]
Toll Free Number 1800 266 0050 [IVR – 1] or Email: msm@nse.co.in
Page 6 of 8
•
The indicator to identify contracts from pre-open and normal market sessions is
referenced in question number 5 of this document.
•
There is no change the format of these files.
14. What information related to pre-open shall be disseminated to website?
Information with respect to Indicative Equilibrium Price, Indicative Equilibrium Quantity of
pre-open session shall be disseminated on website.
15. 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 derivatives segment.
16. Will the Self Trade Prevention Check (STPC) mechanism be applicable during the pre-
open session in the equity derivatives segment?
Yes, the Self Trade Prevention Check (STPC) mechanism will be applicable during the pre-
open session in the equity derivatives segment, in addition to its application in the normal
market.
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.
17. What are the changes in Pre-Trade Risk Controls applicable for Market Price Protection
(MPP) and Limit Price Protection (LPP) to contracts eligible for the pre-open session?
The details of changes applicable for Market Price Protection (MPP) for index futures
contracts and Limit Price Protection (LPP) for index and stock futures contracts are provided
in circular reference no. NSE/FAOP/71092 dated November 03, 2025.
18. What 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"
19. 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 following error messages shall be displayed on the NEAT Terminal for order rejections
during the Pre-Open Session or before the normal market opens:
Scenario
Rejection Message
Error
codes
[Updated on: 01/JUL/26]
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Page 7 of 8
Preopen order for any contract other than the eligible
contracts
Security is not eligible to
trade in Preopen.
16145
Market will validate for DQ, ST, Spread, 2L, 3L orders
will be rejected using these error messages
Spread
allowed
only
when market is open.
16608
DQ
Orders
are
not
allowed in preopen.
16441
ST orders are not allowed
in preopen.
16442
Trading system will validate if Preopen bit is set for
preopen order.
This error code will be
returned for invalid data
in the
order packet.
16419
SL, IOC orders received in preopen session.
Order rejection due to delay in RMS confirmation
Request
Rejected
by
Exchange.
16601
Order rejection from RMS due to insufficient margin
Order
entry
/
Modification rejected by
the Exchange
16725
Trade Cancellation attempted for trades executed
during Pre-open
Trade executed during
pre-open
session
not
allowed to cancel.
16055
Order Entry/ Modification/Cancellation attempted
during buffer period
The markets have not
been opened for trading.
16278
Preopen unmatched orders are cancelled by the
system after preopen session ends.
Order
Cancelled
By
System
16388
Rejection of market order during order entry period
when market orders are restricted
Market
orders
are
currently not allowed
16752
20. 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
[Updated on: 01/JUL/26]
Toll Free Number 1800 266 0050 [IVR – 1] or Email: msm@nse.co.in
Page 8 of 8
21. What message shall be broadcasted on NEAT terminals pertaining to Pre-open session?
Below are messages shall be broadcasted on NEAT terminal for Pre-Open session:
Particular
Message
At start of Pre-Open session
Pre-Open session has started in F&O segment 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
Pre-Open session has ended in F&O segment.
*********************************END*****************************
National Stock Exchange of India Limited
Circular
Department: FUTURES & OPTIONS
Download Ref No: NSE/FAOP/74970
Date: July 01, 2026
Circular Ref. No: 95/2026
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 in F&O Consolidated Circular reference 73928 dated April 28,2026.
As per the aforesaid SEBI circular, the existing Pre-Open session shall be aligned with the CAS framework
and accordingly the following changes shall be applicable in the Pre-Open Session in the Equity Derivatives
segment:
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:
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,
Modification
and
Cancellation for limit orders only
•
No modification/ cancellation allowed
for market orders
•
(*) system driven random closure in
the last 2 minutes
National Stock Exchange of India Limited
Page 2 of 4
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 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 Note:
a) Algo market orders shall be allowed during initial 5 mins of order entry period when both limit
and market orders are allowed.
b) During Order entry period 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”
B. Order matching priority during the Pre-Open session:
Market orders shall be given priority over limit orders. The sequence for order 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.
C. Data Dissemination
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)
National Stock Exchange of India Limited
Page 3 of 4
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
D. Message broadcasted on NEAT terminals:
Below messages shall be broadcasted on NEAT terminal for Pre-Open session:
Particular
Message
At start of Pre-Open session
Pre-Open session has started in F&O segment 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
Pre-Open session has ended in F&O segment.
E. All other features/functionalities as mentioned in Chapter 1.1 Pre-open session section of F&O
consolidated circular 73928 dated April 28, 2026 remain unchanged
Members are requested to note that the circular shall be effective from September 07, 2026. Further, the
functional changes resulting from the implementation of the above shall be available for testing in the mock
trading sessions. Exchange shall issue separate circular w.r.t these mock trading sessions.
Members are advised to load the updated contract.gz and NSE_FO_contract_ddmmyyyy.csv.gz file in the
trading application before trading on the effective date. This file can be obtained from the directory
faoftp/faocommon on the Extranet server. Additionally, members can access the MII contract file -
NSE_FO_contract_ddmmyyyy.csv.gz
on
the
website
path:-
https://www.nseindia.com/all-reports-
derivatives
The updated FAQs related to Preopen session in Equity derivative segment is attached as Annexure A.
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
National Stock Exchange of India Limited
Page 4 of 4
Associate Vice President
Toll Free No
Email id
1800-266-0050 (Option 1)
msm@nse.co.in
