What Is CAS, and Why Did SEBI Introduce It?<\/strong><\/h2>\nEvery day, the closing price of a stock determines your portfolio valuation, the settlement price of derivatives contracts, and the NAV of your mutual funds. Getting this number right matters.<\/span><\/p>\nUntil now, India’s closing price for equity stocks was derived using VWAP – the Volume Weighted Average Price of all trades in the last 30 minutes of the trading day (3:00 PM to 3:30 PM). While widely used, VWAP-based closing prices have a known limitation: they can be influenced by concentrated trading activity in that final window.<\/span><\/p>\nSEBI, in its January 16, 2026 circular, described the objective of CAS as ensuring “a more robust and manipulation-resistant closing price discovery mechanism” that reflects true market demand and supply.<\/span><\/p>\nHere is the simplest way to think about it. Under the old system, your closing price was an average of many transactions spread across 30 minutes. Under CAS, it is an equilibrium price – the single price point at which the highest number of buy and sell orders match each other. It is the price where the market genuinely clears.<\/span><\/p>\n\n
Reference Price:<\/strong> The reference price that anchors the Closing Auction Session (CAS) auction is calculated using the VWAP (Volume Weighted Average Price) of trades from 3:00 PM to 3:15 PM, which is the last 15 minutes of the regular trading session. Orders in the auction window are accepted only within a defined range around this reference price, helping keep the session fair, orderly, and resistant to price manipulation.<\/p>\nSource:<\/strong> SEBI Circular HO\/47\/11\/11(3)2025-MRD-POD2\/I\/2765\/2026, dated January 16, 2026.<\/em><\/span><\/p>\n<\/div>\nHow Does CAS Work? A Simple Timeline<\/strong><\/h2>\nCAS applies to F&O-eligible stocks – stocks that have futures and options contracts available on them. For most actively traded large and mid-cap stocks, this includes names like Reliance Industries, HDFC Bank, Infosys, TCS, ICICI Bank, and hundreds more.<\/span><\/p>\nHere is how a trading day looks from August 3, 2026 onwards:<\/span>
\n<\/p>\n\n
\n\n\n| Time<\/th>\n | What Happens<\/th>\n | Your Experience<\/th>\n<\/tr>\n<\/thead>\n |
\n\n| Up to 3:15 PM<\/td>\n | Regular continuous trading session<\/td>\n | Trade as you normally would. Place, modify, and cancel orders freely.<\/td>\n<\/tr>\n |
\n| 3:15 PM – 3:30 PM<\/td>\n | Closing Auction window – orders collected<\/td>\n | Limit and market orders accepted. No trades execute yet – your order joins the queue. F&O trading continues normally.<\/td>\n<\/tr>\n |
\n| 3:30 PM – ~3:40 PM<\/td>\n | Matching and close derivation<\/td>\n | Orders are matched at the equilibrium price. Official closing price confirmed at approximately 3:40 PM.<\/td>\n<\/tr>\n |
\n| 3:50 PM – 4:00 PM<\/td>\n | Post-close session<\/td>\n | Trades execute at the confirmed closing price for anyone who wishes to trade.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n <\/p>\n \u2190 Swipe horizontally to view full details \u2192<\/div>\n |