New Stock Market Timings From August 3: CAS Begins, F&O Trading Extended to 3:40 PM

The random closure between 3:28 PM and 3:30 PM is intended to reduce last-second order concentration. Once order entry closes, eligible orders will be matched during the final auction phase.

What Is the Closing Auction Session?

The Closing Auction Session is a dedicated end-of-day auction used to determine the official closing price of an eligible stock.

During normal continuous trading, compatible buy and sell orders are matched as soon as they meet in the order book. CAS operates differently.

First, the exchange collects eligible orders. It then identifies an equilibrium price at which the maximum quantity of shares can be executed. Accepted buy and sell orders are matched together at that price, which becomes the stock’s official closing price.

This means the closing price will be based on the combined buying and selling interest submitted during the auction rather than simply being calculated from trades executed during the final 30 minutes.

The new framework is intended to make the closing price more representative of end-of-day demand and supply. However, it does not guarantee that every auction will have high liquidity or that every submitted order will be executed.

Which Stocks Will Be Affected?

CAS will initially apply only to securities in the cash segment on which derivatives contracts are available.

In simple terms, the underlying cash shares of companies available in the F&O segment will be covered first. The NSE will include a CAS identifier in its security master file so brokers and trading platforms can recognize eligible securities.

Stocks without derivatives contracts will not enter CAS in the initial phase. They will continue trading normally until 3:30 PM, and their closing prices will continue to be calculated using the existing methodology.

SEBI may expand CAS to additional securities later, but that would require further guidance and exchange-level operational instructions.

How Was a Stock’s Closing Price Calculated Earlier?

Under the existing system, the official closing price is generally based on the Volume Weighted Average Price, or VWAP, of transactions completed during the final 30 minutes of continuous trading.

VWAP gives greater importance to prices at which a larger number of shares were traded.

For example, suppose:

• 900 shares are traded at ₹100.
• 100 shares are traded at ₹110.
• The final trade takes place at ₹110.

The last traded price may be ₹110, but the volume-weighted closing price would remain closer to ₹101 because most of the volume was executed near ₹100.

This system prevents one small trade near the closing bell from determining the official close. CAS follows the same broad objective of reducing closing-price distortion but uses a collective auction mechanism instead.

For securities that later become ineligible for CAS because their derivatives contracts are discontinued on both exchanges, NSE says the closing-price method will revert to the existing last-30-minute VWAP framework.

How Will the 20-Minute Closing Auction Work?

1. Continuous trading ends at 3:15 PM

Eligible cash-market stocks will trade normally until 3:15 PM.

The exchange will use trading activity before this cut-off to calculate the reference price for the auction.

2. Transition period from 3:15 PM to 3:20 PM

No new orders can be entered in CAS-eligible shares during this five-minute transition period.

Any order submitted during this period will be rejected by the exchange. The reference price and applicable auction price band will also be calculated and communicated during this stage.

3. Market and limit orders from 3:20 PM to 3:25 PM

Investors can place, modify or cancel eligible market and limit orders during this five-minute window.

These orders will be collected in the auction order book. They will not be executed immediately in the manner used during continuous trading.

4. Limit orders only after 3:25 PM

From 3:25 PM until the random auction closure, new market orders will not be accepted.

Existing market orders will become locked and cannot be modified or cancelled. Limit orders may still be placed, modified or cancelled until the system closes order entry randomly between 3:28 PM and 3:30 PM.

5. Order matching from 3:30 PM to 3:35 PM

After the order-entry window closes, no new orders will be accepted.

The exchange will match eligible buy and sell orders and determine the equilibrium price. This becomes the official closing price of the stock.

What Happens to Pending Orders at 3:15 PM?

One of the biggest practical concerns for traders is what happens to open or unexecuted orders when continuous trading ends.

Eligible unexecuted limit orders may be carried forward from the Continuous Trading Session to CAS. These carried-forward orders will generally receive higher time priority than new limit orders entered during CAS.

However, the following orders will not be carried forward:

• Stop-loss orders
• Iceberg orders
• Disclosed-quantity or other ineligible special orders
• Orders outside the revised CAS price band

The exchange will cancel ineligible orders and send the relevant cancellation messages. Orders newly placed outside the permitted auction price range will be rejected automatically.

This is particularly important for traders who leave stop-loss or special orders pending near 3:15 PM.

Why Is SEBI Introducing CAS?

The official closing price is more than the final number displayed on a stock chart.

It may be used for:

• Portfolio valuation
• Index calculations
• Mutual fund and ETF valuation processes
• Performance reporting
• Margin and risk calculations
• Derivatives-related reference and settlement processes

Because so many financial activities rely on the closing price, regulators want the figure to reflect broader end-of-day buying and selling interest.

A dedicated auction also provides institutional investors and large market participants with a common liquidity pool for executing closing-price orders. The objective is to strengthen transparency and price discovery while reducing the influence of isolated trades near market close.

How Will F&O Traders Be Affected?

The normal closing time for the equity derivatives segment will move from 3:30 PM to 3:40 PM.

The extension applies to:

• Index futures
• Index options
• Stock futures
• Stock options

NSE has confirmed that the extended timing applies to both index and stock derivative contracts.

The additional ten minutes may allow derivatives traders to respond after the closing price of underlying CAS-eligible shares has been discovered.

For example, suppose an eligible stock stops continuous trading at ₹500 at 3:15 PM but discovers an auction closing price of ₹506. Its stock futures and options may react during the extended derivatives session.

This does not mean the additional ten minutes will automatically provide better entries or lower risk. Liquidity, spreads and volatility may behave differently during the final window, particularly in less-active contracts.

The derivatives closing price will continue to be calculated using the existing VWAP methodology, but the final 30-minute calculation window will shift to 3:10 PM–3:40 PM.

How Could Intraday Equity Traders Be Affected?

Intraday traders dealing in CAS-eligible cash shares will effectively have only until 3:15 PM to trade through the normal continuous order book.

After that time, orders will be handled according to auction rules.

This may affect traders who usually:

• Exit positions during the final 15 minutes
• Place stop-loss orders close to market closing
• Use iceberg or disclosed-quantity orders
• Depend on immediate execution
• Trade closing momentum in F&O-enabled shares

A trader entering a position at 3:10 PM will have considerably less time to exit through continuous trading than under the earlier market structure.

Broker-level intraday square-off timings may also differ from exchange timings. Traders should therefore verify their broker’s updated Risk Management System and auto-square-off policy rather than assuming positions can remain open until the exchange’s final closing time.

Will Delivery Investors Be Affected?

Long-term investors may experience less operational impact than active intraday traders, but they should still understand how CAS works.

A delivery investor placing an order in an eligible stock after 3:20 PM will be participating in an auction. The order will not necessarily execute immediately.

Execution will depend on:

• The submitted order type
• The auction price band
• The final equilibrium price
• Available matching quantity
• Order priority
• Whether the auction discovers a valid closing price

Investors who do not require closing-price execution may find it simpler to place their orders during normal continuous trading rather than waiting for CAS.

Could NSE and BSE Have Different Closing Prices?

Yes.

NSE has stated that the reference prices, applicable price bands and closing auctions will be calculated independently by each exchange.

Therefore, the same stock could potentially discover slightly different official closing prices on NSE and BSE, depending on the orders and liquidity available on each platform.

This is not necessarily an error. It is a consequence of each exchange maintaining a separate auction order book.

ICFM Analysis: Is the New System Good for Traders?

From a market-structure perspective, CAS is a meaningful change because it separates continuous trading from closing-price discovery.

The auction may offer three broad advantages:

• A larger pool of end-of-day orders may contribute to price discovery.
• The closing price may become less dependent on a few late continuous-market trades.
• F&O traders receive an additional window to react after the cash-market closing auction.

However, retail traders should not interpret CAS as an opportunity to trade without risk.

The final session may create new challenges, including unfamiliar order behaviour, possible order cancellations and uncertainty about the equilibrium price. Traders who normally act during the last few minutes will need to update their routines.

Our view: The system may improve the quality of closing-price discovery over time, but the initial transition could cause confusion among traders who do not understand the difference between continuous trading and auction-based matching.

What Should Traders Do Before August 3?

Before the revised market timings take effect, traders should:

• Identify which stocks are eligible for CAS.
• Review their broker’s revised market and square-off timings.
• Avoid leaving unmanaged stop-loss orders near 3:15 PM.
• Understand the difference between market and limit orders in CAS.
• Check whether pending orders were carried forward, cancelled or rejected.
• Avoid assuming that an auction order guarantees execution.
• Update automated strategies and trading-system time conditions.
• Review F&O risk until the new 3:40 PM close.
• Keep sufficient margin available for new or modified CAS orders.

NSE has clarified that new CAS orders and modified carried-forward orders will remain subject to applicable order-level margin requirements.

Final Takeaway

The new stock market timings from August 3 will significantly change the final part of India’s trading day.

Continuous trading in eligible F&O-linked cash shares will end at 3:15 PM, after which their official closing prices will be determined through the Closing Auction Session. Non-F&O shares will continue trading until 3:30 PM, while index and stock derivatives will remain open until 3:40 PM.

For investors, the change primarily affects how closing prices and auction orders work. For intraday and F&O traders, it may require changes in execution timing, stop-loss management, hedging and end-of-day risk control.

The most important step is not simply remembering the new closing time. Traders must understand which market segment they are trading, what type of order they are using and how that order will be treated after 3:15 PM.

Disclaimer: This article is intended only for educational and informational purposes. It is not investment advice or a recommendation to buy, sell or hold any security. Stock-market and derivatives trading involve financial risk. Traders should review official exchange circulars and broker-level operational guidelines before placing orders.

Frequently Asked Questions

When will the new stock market timings start?

The revised framework will become effective from Monday, August 3, 2026.

Will the entire cash market close at 3:15 PM?

No. Only CAS-eligible shares will stop continuous trading at 3:15 PM. Non-F&O securities will continue normal trading until 3:30 PM.

Does CAS apply directly to futures and options contracts?

No. CAS applies to eligible shares in the equity cash segment. Equity derivatives will continue trading separately until 3:40 PM.

Can traders place orders between 3:15 PM and 3:20 PM?

No. Order entry will not be permitted during the transition and reference-price calculation period. Orders submitted during this window will be rejected.

Can market orders be cancelled after 3:25 PM?

No. After 3:25 PM, market orders cannot be modified or cancelled. Only eligible limit orders may be entered, modified or cancelled until the random closure.

Are IOC orders allowed during CAS?

No. Immediate-or-Cancel orders will not be permitted during the Closing Auction Session.

Will F&O trades continue until 3:40 PM?

Yes. The revised timing applies to index futures, index options, stock futures and stock options.

Will broker intraday positions also remain open until 3:40 PM?

Not necessarily. Brokers can maintain their own RMS and auto-square-off cut-offs. Traders should check the specific policy issued by their broker.

Is the pre-open market also changing on August 3?

No. NSE’s FAQ states that CAS will begin on August 3, 2026, while the separate alignment of the pre-open auction framework is scheduled for September 7, 2026.