Key Takeaways :

• CAS is SEBI's new auction mechanism for deciding the official closing price of select equity shares, replacing the old 30-minute VWAP method.
• Only Category I equity shares, those with active F&O contracts on NSE and BSE, are covered in Phase I, effective August 3, 2026.
• Continuous trading for these equity shares ends at 3:15 PM instead of 3:30 PM, with the auction and a post-close session filling the window until 4:00 PM.
• F&O trading hours are extended to 3:40 PM to stay aligned with the later cash market close.
• Timings for intraday square-off, GTT trigger, and price alert notifications for equity shares that fall under the CAS ambit have been advanced; make sure you review the same with your broker before placing any late-day orders.

What Is the Closing Auction Session (CAS) for Equity Shares ?

If you trade or hold equity shares in India, the way your stock's closing price gets calculated is changing. Effective August 3, 2026, SEBI introduced the Closing Auction Session (CAS) for the equity cash segment. It changes both the trading times near the end of the day and the way the closing price for your equity shares is determined.

This is more important than one may think. The closing price of the equity share is incorporated into the calculation of the Nifty, Sensex, mutual fund NAVs, futures and options settlements, and even the valuation of your personal portfolio. When you are deciding to make an equity investment, it is helpful to know exactly what is changing.

Why SEBI Introduced CAS

For years, the closing price of equity shares was calculated using the Volume Weighted Average Price (VWAP) of trades in the last 30 minutes of the session, roughly 3:00 PM to 3:30 PM. It worked reasonably well, but a handful of large orders placed in that final window could still nudge the closing price away from where the stock traded for most of the day.

CAS introduces a call auction instead of the last period of continuous trading for certain shares. This means that orders are aggregated and not immediately matched, while the exchange computes a single price at which the greatest number of shares is traded. This price serves as the official close. It’s nothing new worldwide, as the NYSE and London Stock Exchange have been conducting closing auctions for some time.

Which Equity Shares Are Covered

CAS is rolling out in phases, and Phase I doesn't apply to every listed company. SEBI has split the equity cash segment into two categories:

• Category I: Equity shares with active Futures & Options (F&O) contracts on both NSE and BSE. These move into CAS from August 3, 2026.

• Category II: Every other listed stock, which continues with the existing VWAP-based closing method for now.

   

If you're deciding which equity to invest in this month, check whether the stock carries F&O contracts. If it does, its closing price mechanism has already changed.

For equity shares covered under the Closing Auction Session (CAS), the Equity Cash Segment will follow the revised trading schedule below: 

Equity shares outside Category I continue to trade regularly until 3:30 PM and remain unchanged.Since F&O contracts settle against the equity cash closing price, and that price is now finalised later, derivatives trading has been extended by 10 minutes, to 3:40 PM, keeping cash and F&O aligned instead of settling contracts before the underlying equity shares have a confirmed close.

What This Means for Your Orders

Key Changes During the Closing Auction Session (CAS)

If you trade in equity shares covered under the Closing Auction Session, keep these important changes in mind:

• Order entry timings: Both market and limit orders can be placed from 3:15 PM to 3:25 PM. From 3:25 PM to 3:30 PM, only limit orders are allowed.
• Special order types not allowed: Stop Loss (SL), Immediate or Cancel (IOC), and Disclosed Quantity (DQ) orders cannot be placed during the CAS window.
• No trade cancellations: Once a trade is executed during the Closing Auction Session, it cannot be cancelled. Any unexecuted orders remaining at the end of CAS are automatically cancelled by the Exchange.
• Revised price band: During CAS, a ±3% price band from the reference price applies for eligible equity shares.
• Intraday (MIS) positions: Since continuous trading ends at 3:15 PM for CAS stocks, brokers may advance their auto square-off timings for MIS positions.
• Price Alerts and GTT orders: For CAS-based stocks, these orders remain active only until 3:15 PM, unlike other stocks where they continue until 3:30 PM.
• Orders placed after 3:15 PM: Regular orders entered after 3:15 PM are not executed immediately and are carried forward to the next trading session, unless they are eligible CAS orders.
• Plan your exits: If you usually exit positions close to market closing, consider placing your orders at least 5 minutes before the cutoff to avoid missing the applicable trading window.

Common Doubts About CAS

Does CAS directly affect my mutual fund or ETF units?

Not directly, but indirectly, since NAVs use the closing prices of the underlying equity shares. A more stable, auction-derived close should reduce last-minute NAV swings.

Is CAS the same as the pre-open session?

 No. The pre-open auction sets the opening price at the start of the day; CAS is a separate auction near the end that sets the closing price. SEBI is also restructuring the pre-open session from September 7, 2026, under the same circular.

H3: Does this affect long-term investors the same way as traders?

Less so. You would be buying equity to hold onto it long-term, so the effect daily would be minimal. But now, when you value your portfolio at night, you would be using the price generated from an auction for those stocks eligible for F&O trading.

How mastertrust Helps You Navigate the New CAS Rules

Keeping up with exchange-level changes like CAS shouldn't be something you piece together on your own. mastertrust keeps its trading platform and client communication aligned with SEBI, NSE, and BSE circulars, so square-off timings, GTT cutoffs, and order windows for CAS-covered equity shares reflect the current rules.

You can open a demat and trading account with mastertrust to get started. On pricing, mastertrust charges a straightforward ₹20 per order for intraday, F&O, and equity trades, so adjusting to the new timings doesn't come with a pricing surprise. 

Final Thoughts

The introduction of CAS is not a trigger to alter your investment strategy. Still, it definitely is a trigger to adjust your timing if you trade equity shares alongside F&O contracts. The previous method of using a 30-minute average to determine the closing price has been replaced by the auction method, in which orders are pooled, and the price at which the highest volume of stock can be traded is determined. Whether you actively trade or invest in equity in the coming years, it is crucial to understand whether you have shares that fall under this category.

Frequently Asked Questions (FAQs):

1. On which date was CAS made applicable for equity shares?

CAS came into effect on August 3, 2026, in relation to Category I equity shares with active F&O contracts at the NSE and BSE.

2. What is the closing time for CAS covered equity shares?

Continuous trading ends at 3:15 PM, followed by the auction period and post-trade processing period up until 4:00 PM.

3. Do all equity shares fall under CAS?

No. Only Category I equity shares are covered in Phase I. Other listed equity shares continue with the previous VWAP-based method.

4. How does CAS affect intraday traders?

Intraday (MIS) auto square-off timings on CAS-covered equity shares have moved earlier, since continuous trading now ends at 3:15 PM instead of 3:30 PM.

5. Does CAS change how I should pick equity to invest in?

Not fundamentally. Fundamentals, valuation, and your own goals still matter most. CAS changes how the closing price is calculated for stocks with F&O contracts, useful context if you trade near market close.