What is the Closing Auction Session (CAS)? Everything Investors Should Know

Market Closing Process at a Glance

Continuous Trading (Till 3:15 PM) → Reference Price Calculation (3:15–3:20 PM) → Order Entry (3:20–3:25 PM) → Limit Orders & Random Closure (3:25–3:30 PM) → Order Matching & Closing Price (3:30–3:35 PM)

Have you ever thought about how the closing prices of stocks are determined?

At the end of each trading day, every listed stock has an official Closing Price. This may differ from the last traded price and is a key benchmark for calculating stock market indices, valuing mutual funds and ETFs, settling trades, and assessing portfolio values.

To improve transparency in determining the Closing Price and ensure it better reflects market demand and supply, the stock exchanges have introduced the Closing Auction Session (CAS) as part of the regulatory framework approved by the Securities and Exchange Board of India (SEBI).

The new framework will be implemented in phases, beginning on 3 August 2026, initially applying to Eligible Scrips, which are stocks with listed derivative contracts.

What is the Closing Auction Session (CAS)?

The stock exchanges are introducing the Closing Auction Session (CAS), a short auction conducted after the Continuous Trading Session (CTS) ends, effective 3 August 2026.

Earlier, the Closing Price for eligible stocks was generally determined using the Volume Weighted Average Price (VWAP) of trades executed during the final 30 minutes of the Continuous Trading Session. Under the revised framework, the Closing Price will now be determined by the Equilibrium Price discovered during the Closing Auction Session.

During the Closing Auction Session, traders and investors can place buy and sell orders. The exchange identifies the price at which the maximum number of buy and sell orders can be matched.

This price is known as the Equilibrium Price, and it becomes the stock’s official Closing Price for that trading day.

Since all eligible buy and sell orders are considered together before matching, the Closing Price is expected to better reflect actual market demand and supply.

In simple terms, the Closing Auction Session helps ensure that a stock’s Closing Price is more transparent, reliable, and representative of genuine market activity at the end of each trading day.

Why has SEBI introduced CAS?

As per the SEBI-approved regulatory framework, the objective of introducing the Closing Auction Session is to improve the way the Closing Price is determined.

The key objectives are to:

• Improve price discovery by matching actual buy and sell orders.
• Strengthen the reliability and transparency of the Closing Price.
• Enhance market efficiency and market integrity.
• Align Indian market practices with leading global exchanges.

What has changed from 3 August 2026?

The biggest change is in the market closing process for Eligible Scrips.

Earlier	Now
Continuous Trading Session (CTS) continued until 3:30 PM.	Continuous Trading Session (CTS) ends at 3:15 PM.
There was no dedicated Closing Auction Session.	A dedicated Closing Auction Session (CAS) is conducted after continuous trading ends.
The Closing Price was generally determined using the Volume Weighted Average Price (VWAP) of trades during the final 30 minutes of trading.	The Closing Price is determined through the Equilibrium Price discovered during the Closing Auction Session.

How does the Closing Auction Session work?

The Closing Auction Session follows the timeline prescribed by the stock exchanges.

Time	Stage	What Happens?
3:15 PM – 3:20 PM	Transition to CAS & Reference Price Calculation	The Continuous Trading Session ends, and the exchange calculates the Reference Price using the prescribed methodology before the Closing Auction Session begins.
3:20 PM – 3:25 PM	Order Entry Period	Investors can place Market Orders and Limit Orders, as well as modify or cancel eligible orders.
3:25 PM – Random Closure (between 3:28 PM and 3:30 PM)	Limit Order Period	Only Limit Orders are accepted. The Order Entry Period closes randomly between 3:28 PM and 3:30 PM to discourage last-minute order placement and promote fair price discovery.
3:30 PM – 3:35 PM	Order Matching	Buy and sell orders are matched at the Equilibrium Price, which becomes the official Closing Price.

Note: Initially, the Closing Auction Session applies only to Eligible Scrips. Trading hours for other equity stocks remain unchanged.

What does this mean for investors?

For most long-term investors, this change does not require any change in investment strategy.

However, if you actively trade in Eligible Scrips, you should be aware of the revised market timings and the Closing Auction Session.

Overall, the new framework is designed to improve confidence in the market by strengthening the process used to determine the official Closing Price.

Disclaimer: This article is for educational purposes only and should not be construed as investment advice or a recommendation to buy or sell any securities. Investors are advised to read the relevant SEBI and exchange circulars before making investment decisions.

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