NSE's New Closing Price Rule (CAS), Explained

Starting August 3, 2026, the last 15 minutes of trading will work differently for stocks with F&O contracts. Here's what NSE's new Closing Auction Session means for your portfolio.
NSE's New Closing Price Rule (CAS), Explained

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Starting August 3, 2026, the National Stock Exchange (NSE) and Bombay Stock Exchange (BSE) are introducing the Closing Auction Session (CAS) in the equity cash segment. This changes how the official closing price is determined for certain stocks. Here's what it means for your trading.

Quick Facts

  • Effective date: August 3, 2026
  • Applicable securities: Stocks with listed derivative contracts. In this initial phase, CAS applies only to stocks on which derivative (F&O) contracts are available.
  • CAS timing: 3:15 PM to 3:35 PM, on all trading days

How It Works

Normally, a trade executes the moment a buyer and seller agree on a price. CAS works differently. Buy and sell orders for eligible securities are collected first, and only matched at the end, at one single price for everyone. That price, based on overall market demand and supply, becomes the stock's official close for the day.

The New Timings

What's HappeningWhen
Normal trading9:15 AM to 3:15 PM
Intraday positions auto square-off window3:05 PM to 3:10 PM
Closing Auction Session (CAS) window3:15 PM to 3:35 PM
Transaction period, no order execution for stocks with derivative contracts3:15 PM to 3:20 PM
Market and Limit orders — place, modify or cancel3:20 PM to 3:25 PM
Limit orders only — place, modify or cancel3:25 PM until random close (between 3:28 and 3:30 PM)
Derivatives trading session closes3:40 PM
Post-close session3:50 PM to 4:00 PM

What Changes for You

Eligible stocks will trade during this window, but not in the usual way. Every order goes into the same pool and gets matched at one common price, so nothing executes the instant you place it. If your order doesn't get matched by the end of the session, it's simply cancelled — it won't carry over. This matched price becomes the stock's closing price for the day.

Does This Affect You?

This affects the last 15 minutes of trading in any stock that has listed F&O contracts. If you trade stocks without F&O contracts, or you just hold mutual funds, you won't see this in your day-to-day trading. You'll get 10 extra minutes for trading F&O.

This is general information for awareness and does not constitute investment advice. For assistance, please contact your broker.

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