Closing Auction Session Goes Live on NSE and BSE: A New Official Close for F&O Stocks

What the New 3:15 pm Closing Auction Changes for F&O-Eligible Stocks

The National Stock Exchange and BSE have begun rolling out a dedicated Closing Auction Session, or CAS, for eligible stocks. The change follows a SEBI framework circular issued on January 16, 2026, and went live on the exchanges from August 3, 2026. In the first phase, the auction applies only to equity cash-segment stocks on which derivative contracts are available. For those securities, the official closing price is now discovered through a structured auction rather than relying on the earlier end-of-day method.

The new timetable runs from 3:15 pm to 3:35 pm on NSE, with a transition buffer until 3:50 pm and the post-close session from 3:50 pm to 4:00 pm. BSE follows the same broad time blocks. The first five minutes, from 3:15 pm to 3:20 pm, are used for transition and reference price calculation. Order entry begins at 3:20 pm; no trades take place during the collection phase. From 3:25 pm to 3:30 pm, only limit orders can be added, modified or cancelled, while market orders are locked and the system may randomly stop order entry during the last two minutes.

The important divide is eligibility. CAS-eligible securities get a closing price set through the auction if an equilibrium price is found. If no equilibrium price is discovered, the closing reference price is used. Securities outside CAS continue under the previous mechanism, which BSE describes as the volume-weighted average price of the last 30 minutes of continuous trading. Non-CAS securities also continue trading until 3:30 pm, while the equity derivatives segment runs until 3:40 pm.

Why the Reference Band, Order Restrictions and Tie-Break Rules Set the Final Print

NSE and BSE Can Print Different Closes for the Same Stock

The exchanges maintain separate CAS order books, so the buy and sell interest available on each venue can differ. As a result, the same stock may close at one equilibrium price on NSE and a different equilibrium price on BSE. That is a break from the mental model of a single official close, and it matters for anyone using the print for valuation, settlement references or index-style tracking.

The ±3% Band Anchors the Auction Around the 3:00–3:15 VWAP

Before matching begins, the exchange calculates a reference price using the volume-weighted average price of trades executed between 3:00 pm and 3:15 pm. The auction then operates within a ±3% band around that reference price, and orders outside the band are excluded. For a stock with a reference price of ₹100, only orders between ₹97 and ₹103 can participate. This structure keeps the closing print from moving too far from recent continuous trading, but it can still vary from the stock's last traded price.

Market Orders Lose Their Usual Protection

One of the most practical changes is that Market Price Protection does not apply during CAS. A market order therefore enters the auction's price-discovery mechanism without the normal MPP control. Self-Trade Prevention remains active, with potentially self-matching orders cancelled by default. Stop-loss, iceberg and revealed-quantity orders are not allowed in CAS, and eligible stop-loss orders from continuous trading are not carried forward into the auction.

The equilibrium price itself is not simply the last price. The exchange first seeks the price at which the maximum quantity can be executed. If more than one price can trade the same maximum quantity, it chooses the one with the minimum absolute order imbalance. If a tie still remains, it selects the price closest to the reference price, with NSE adding a midpoint rule where the reference price itself can win.

Trading Around CAS: The Timetable and Controls That Matter

• Check eligibility before trading the final minutes: Phase 1 covers only equity cash-segment stocks with derivative contracts. Other stocks still close using the last-30-minute VWAP.
• If you use market orders near the close, place them in the 3:20–3:25 pm entry window. From 3:25–3:30 pm, market orders cannot be modified or cancelled, and Market Price Protection is not available.
• Avoid relying on stop-loss, iceberg or revealed-quantity behavior inside CAS. These order types are not accepted, and eligible stop-loss orders are not carried forward from continuous trading.
• Use limit orders if you need to retain control during the later collection phase. Only limit orders remain adjustable after 3:25 pm, and carried-forward limit orders retain time priority on BSE unless modified during CAS.
• Do not assume a single official close. NSE and BSE run separate CAS books, so the same stock can close at different prices on the two exchanges.