What is a Closing Auction Session: A Complete Guide for Retail Investors

The closing price is one of the most crucial aspects of the securities market. The closing price in the equities segment is used to assess investment portfolio values, calculate NAVs of mutual fund schemes, settle derivative contracts, calculate index values, and evaluate the daily share price performance.

The capital market regulator, the Securities and Exchange Board of India (SEBI), unveiled the Closing Auction Session (CAS) for eligible securities in the equity cash segment on January 16, 2026. The new framework became effective on August 3, 2026, and replaces the previous Volume-Weighted Average Price (VWAP)-based closing price mechanism for eligible securities, which used an auction-based price discovery process.

This new mechanism aims to enhance market integrity, improve price discovery, minimise price manipulation before market closing, and align the Indian securities market with international best practices. In this article, you will learn everything you need to know about the Closing Auction Session.

What is a Closing Auction Session?

A closing auction session is a dedicated trading session conducted immediately after the regular trading session. The CAS is conducted from 3:15 P.M. to 3:30 P.M. on trading days. During this session, market participants place buy and sell orders, which are executed at an equilibrium price.

Unlike continuous trading sessions, where share prices change every second based on the orders placed, the Closing Auction Session generates a single closing price through an auction-based price discovery process. This is the official price used to close all the eligible stocks.

The main objective of the Closing Auction Session is to ensure that the closing price reflects the real demand and supply in the market rather than being influenced by t last-minute trades that could affect valuations.

The closing price is extremely important for the financial markets. This is because it is often used in:

• Portfolio valuation daily
• Calculation of Mutual Fund NAVs
• ETF Valuation
• Index Calculation
• Mark-to-market settlement of derivatives positions
• Institutional Portfolio Reporting
• Company performance measurements

Even a slight change in the closing price can result in significant differences in institutional portfolios worth several thousand crore rupees.

What Changed Under SEBI’s New Circular?

The Closing Auction Session (CAS) for the equity cash segment aims to improve price discovery in Indian stock exchanges. This was made effective on August 3, 2026. The key change is that the official closing price of eligible securities will now be determined through an auction process instead of the VWAP methodology previously used.

Under the new method, the buyers and sellers of securities will be able to place their orders in the Closing Auction Session. Through these orders, the exchange will arrive at the equilibrium price, the price at which the maximum number of shares can be matched, and this will become the closing price of the security.

Apart from introducing the CAS, SEBI has also made changes in the pre-open auction session.

The aims of all these changes are as follows:

• Improvement in price discovery.
• Prevention of price manipulation at the end of the day.
• Improvement in market transparency.
• Arrival at a more representative closing price.
• Alignment of Indian practice with international standards.

How Does a Closing Auction Session Work?

Effective August 3, 2026, SEBI introduced the Closing Auction Session (CAS) to determine the closing price of eligible securities through an auction-based price discovery process as opposed to the earlier volume-weighted average price (VWAP) method.

Under the new framework, the closing price is no longer determined by trades executed during the last few minutes of the trading session. Instead, it is determined through an auction process after the close of the regular trading session. This allows the stock exchange to arrive at an equilibrium price at which the maximum number of shares can be traded. As a result, the closing price truly represents the equilibrium of demand and supply in the market.

Closing Auction Session Timings

Is There Any Impact on Stock Market Timings?

Pre-Open Session Timeline

Stocks and MTF

Intraday Auto Square-off Timings

Also Read: What is Intraday Trading? Complete Guide For Traders

Derivatives Segment

How is Equilibrium Price Determined?

The exchange evaluates every possible price level and determines the price at which the highest trading volume can occur.

The closing price or equilibrium price must satisfy three key objectives:

• Maximum tradeable volume
• Minimum order imbalance
• Fair price discovery

If multiple prices meet these criteria, the exchange uses preset tie-breaker rules to determine the final price. This approach ensures that the closing price depends not on a couple of transactions but on the market as a whole.

Note: If no equilibrium price is discovered, then the reference price itself shall be the closing price.

Let us understand this with an example:

Buy Orders

Sell Orders

The exchange calculates cumulative buy and sell quantity at each price level

As ₹503 allows the maximum executable quantity (2,000 shares), it will be the equilibrium price or the closing price.

The method above represents the intention of all participating buyers and sellers. Hence, it provides a better representation of the market than relying solely on trades made during the last minutes of continuous trading.

Are All Securities Covered Under Closing Auction Session?

According to the circular issued by SEBI, the Closing Auction Session in the first phase will apply to cash market securities belonging to the Futures & Options (F&O) segment.

Such securities tend to be characterised by the following:

• Higher trading volume
• Better liquidity
• Institutional participation
• A major impact on derivatives markets

It is important to note that the closing price for the remaining securities in the cash segment shall continue to be determined based on the VWAP of trades executed during the last 30 minutes of the CTS in the cash segment.

• Securities Outside CAS: Trading will continue up to 3:30 P.M. The closing price will be determined using the existing VWAP method.
• Equities Derivative Market: Trading will continue up to 3:40 P.M. on all trading days.
• Post-market session (cash market): A post-market trading session will be conducted from 3:50 P.M. to 4:00 P.M., during which all trades will be executed at the closing price of the corresponding stock.

Why Did SEBI Introduce Closing Auction Session?

The primary objective of SEBI in introducing the Closing Auction Session is to enhance the integrity of the capital market.

• Better Price Discovery: The auction-based pricing mechanism includes both buying and selling interests at the end of the trading period, resulting in a more accurate and efficient determination of a better closing price.
• Reduced Market Manipulation: Under the earlier Volume-Weighted Average Price (VWAP) system, a few large trades placed near the end of the trading session could significantly affect the closing price. The auction-based system addresses this issue by using a transparent price discovery process to determine the closing price, thereby making it much harder to manipulate.
• Improved Institutional Participation: Large mutual funds, pension funds, insurance companies, and foreign portfolio investors execute most of their trades at the end of the trading day. It would therefore be a more effective process than trading by other means.
• Greater Market Transparency: As the closing price is calculated using predetermined exchange rules, the process is transparent and consistent with all the market participants.
• Alignment with Global Standards: Most international stock exchanges, including those in the US and Europe, have adopted closing auctions for arriving at the official closing price.

Key Differences Between CTS and CAS

FAQs

What is the Closing Auction Session (CAS)?

The Closing Auction Session is a dedicated trading session conducted after regular market hours to determine the official closing price of eligible securities through an auction-based price discovery mechanism.

When did the new Closing Auction Session become effective?

The framework came into effect on 3 August 2026, following SEBI's circular issued on 16 January 2026.

How is the closing price determined under the Closing Auction Session?

The exchange collects buy and sell orders during the auction period and identifies the equilibrium price at which the maximum quantity of shares can be traded. This equilibrium price becomes the official closing price.

Can I modify or cancel my order during the auction?

Yes. During the order collection period, investors can generally place, modify, or cancel eligible orders. Once the order collection period ends, modifications are no longer permitted.

Which securities are covered under the Closing Auction Session?

Initially, the Closing Auction Session applies to eligible securities specified by the stock exchanges, particularly stocks in the Futures & Options (F&O) segment, in line with SEBI's framework.

How does the Closing Auction Session benefit retail investors?

The auction mechanism provides a more representative closing price, improving portfolio valuation, reducing the impact of end-of-day volatility, and promoting fairer price discovery.