What is CAS?
SEBI has introduced a new 20-minute auction window at the end of the trading day to determine the closing price for stocks that have F&O contracts. This replaces the earlier method of using the last 30 minutes of continuous trading to arrive at the closing price. CAS goes live from 03 Aug 2026.
What are the changes in schedule and timing?
The updated market timings are as follows:
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3.15-3.20 pm: Reference price is calculated. Order entry via SmartAPI will be rejected in this phase.
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3.20-3.25 pm: Limit and Market orders can be placed, modified, or cancelled.
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3.25-3.30 pm: No changes or cancellations on Market Orders. Limit orders can still be placed/modified. Random close anytime between 3:28 pm and 3:30 pm.
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3.30-3.35 pm: Orders are matched against each other, and the closing price is set.
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3.35-3.50 pm: Transition from CAS to Post-closing session
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3.50-4.00 pm: Trades settle at the Equilibrium Price discovered in the auction.
What order type restrictions will be in place?
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Stop-loss and Iceberg orders for CAS-eligible stocks are disallowed between 3:15-3:40 pm.
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After 3:25 pm, Market orders can no longer be modified or cancelled – only added or changed as Limit orders.
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F&O trading in NFO and BFO will be extended till 3:40 pm on all trading days.
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Changes to post-closing session apply to all stocks, regardless of whether they are CAS-eligible or not.
Changes in Auto-Square Off Timings
For intraday trades, the auto-square off timings will see the following changes from 03 Aug 2026.
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Equity Robo Orders: 3:05 pm
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Equity MIS Orders: 3:10 pm
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Equity F&O Orders: 3:20 pm
How to check if a stock is CAS-eligible?
A new field, is_cas_enabled, is now available in the instrument master response. Check out the sample:
{
"token" : "99926000",
"symbol" : "Nifty 50",
"name" : "NIFTY",
...
"is_cas_enabled" : true
}
A new field, referenceLimitPrice in our Market Data API can be used to get the Reference Price. Here’s a sample response:
{
"status": true,
...
"high": "191.25",
"low": "185",
"close": "187.80",
"referenceLimitPrice": "191",
}
What are “Reference Price” and “Equilibrium Price”?
The Reference Price is fixed at the start of CAS – it's the VWAP of trades between 3:00-3:15 pm (or LTP/previous close if no trades), and it sets the ±3% band within which CAS orders can be placed.
The Equilibrium Price is discovered at the end of CAS – it's the price at which the maximum quantity of orders placed during the auction get matched, using volume maximisation.
In short: Reference Price is the starting boundary for the auction, Equilibrium Price is its outcome. The Equilibrium Price becomes the stock's closing price for the day; if none is discovered, the Reference Price is used instead.
Where to get more detailed information?
You can view our full API documentation here: https://smartapi.angelone.in/docs/CASDoc
For additional reading:
“NSE To Bring Closing Auction Session: What Does It Mean for Stock Prices and Investors?” on Angel One
“SEBI Introduces Closing Auction Session to Enhance Equity Market Price Discovery” on Angel One
BSE’s official circular published on 10 Jun 2026
NSE’s official circular published on 29 May 2026
SEBI’s official circular published on 16 Jan 2026