What Changed at Market Close?
Starting August 3, 2026, the NSE implemented a 'Closing Auction Session' (CAS) for all stocks available in the Futures & Options (F&O) segment. Previously, the closing price for all stocks was the Volume Weighted Average Price (VWAP) of all trades occurring
in the final 30 minutes, from 3:00 PM to 3:30 PM. This method, while functional, was susceptible to distortion from large, last-minute trades. The new CAS aims to discover a more robust and fair closing price by aligning with global best practices and making the close harder to manipulate.
How the New Closing Auction Works
For F&O-eligible stocks, the trading day now looks different. Continuous trading stops at 3:15 PM. This is followed by a multi-stage auction process that runs until about 3:35 PM. Between 3:20 PM and 3:30 PM, investors can place buy and sell orders (both market and limit) into the auction system. The exchange's system then calculates an 'equilibrium price'—the single price at which the maximum number of shares can be traded. This price becomes the official closing price for the day. All other stocks that are not in the F&O segment continue to trade normally until 3:30 PM, with their closing price still determined by the 30-minute VWAP method.
LTP vs. Official Close: The Crucial Difference
This new process creates two key end-of-day prices for F&O stocks: the Last Traded Price (LTP) and the Official Closing Price. The LTP is simply the price of the final trade during the continuous session, which ends at 3:15 PM for these stocks. However, the Official Closing Price is the equilibrium price determined later in the Closing Auction Session. This auction price is the one used for all official purposes: settling F&O contracts, calculating the Net Asset Value (NAV) for mutual funds, valuing your portfolio in your demat account, and forming the basis of daily charts.
Why This Distinction Improves Your Analysis
Relying on the LTP at 3:15 PM can now be misleading. A sudden spike or dip in the final moments of continuous trading might be reflected in the LTP, but it might not represent the broader market consensus. The closing auction, by design, gathers a wider pool of buy and sell interest to find a more stable and representative price. Using the Official Closing Price ensures your analysis is based on the same data that institutional players, like mutual funds and index trackers, use for their own official valuations. This leads to more accurate daily profit and loss calculations, more reliable back-testing of trading strategies, and a truer picture of your portfolio's value at the end of the day.
How to Find and Use the Official Closing Price
So, how do you ensure you're using the right number? Most brokerage platforms and financial news sites will show the LTP during the day, but they update to the Official Closing Price after the auction session concludes (around 3:40 PM or shortly after). The most reliable source is the NSE's official website itself, which publishes daily reports and 'Bhavcopy'—a comprehensive file of all end-of-day data, including the official close for every security. For accurate post-market analysis, make it a habit to wait until after 3:45 PM and confirm the final closing price from a reliable source rather than just noting the last price you saw at 3:15 PM.
