THEBUSINESSBYTES
BUREAU
MUMBAI, AUGUST 4, 2026
The National Stock Exchange (NSE) on Monday implemented the
Closing Auction Session (CAS) for stocks with derivative contracts, marking a
significant reform in the price discovery mechanism aimed at enhancing
transparency and ensuring fair and robust determination of closing prices under
the guidance of the Securities and Exchange Board of India (SEBI).
The exchange said the phased rollout, effective from August
3, 2026, will initially cover stocks in the cash segment on which derivative
contracts are available, while the closing price for the remaining cash market
securities will continue to be determined through the volume weighted average
price (VWAP) of trades executed during the last 30 minutes of the continuous
trading session.
Under the new framework, the CAS will operate as a separate
20-minute session between 3:15 pm and 3:35 pm on all trading days. The session
comprises a five-minute reference price calculation period, followed by five
minutes allowing both market and limit order entries, another five minutes
restricted to limit order entries, and a system-driven random closure during the
final two minutes before order matching. Meanwhile, the equity derivatives
segment will continue trading until 3:40 pm.
NSE said the reference price for a stock during the closing
auction will be based on the VWAP of trades executed between 3:00 pm and 3:15
pm, while the last traded price will serve as the reference in the absence of
trades during the period. A price band of plus or minus three per cent from the
reference price will apply during the auction session, with stock futures
aligned to the same price band. Only market and limit orders will be accepted,
while iceberg and stop-loss orders will not be permitted.
The exchange said the closing price will be determined using
an equilibrium price mechanism under which the maximum executable volume is
matched, with market orders receiving priority over limit orders. Unexecuted
limit orders from the continuous trading session will be carried forward to the
closing auction, subject to specified conditions, while the existing cash
market risk management framework will remain applicable during the session.
NSE also clarified that the index graph during the auction
session should be interpreted carefully as there is no continuous order
matching between 3:15 pm and 3:30 pm. Consequently, the displayed index value
remains constant during this period even though indicative values based on
equilibrium prices are continuously calculated and displayed alongside market
quotes on the exchange's website.
The exchange noted that separate order books are maintained for the closing auction session and the continuous trading session, resulting in potential differences in stock prices and index values. It added that a study of pre-open call auction sessions between 2014 and 2024 found more than 8.5 lakh scrip-days where opening price differences exceeded two per cent.
On the first day of implementation, the closing auction recorded participation from 515 trading members who placed orders for 56,773 unique Permanent Account Numbers (PANs), exceeding the pre-open call auction session, where 403 trading members placed orders for 42,822 unique PANs. The exchange described the debut participation as encouraging and said it expects the mechanism to mature further with increased adoption over time.
