The Closing Auction Session (CAS)

Source-grounded foundation

• The Closing Auction Session (CAS) is a dedicated 20-minute daily auction mechanism introduced in the cash market segment for equity stocks on which derivative (F&O) contracts are available.
• Instead of computing closing prices through continuous trade averages, CAS aggregates buy and sell orders to discover a single, fair equilibrium closing price.
• Regulator Mandate: Mandated by the Securities and Exchange Board of India (SEBI) via circular issued on January 16, 2026.
• Exchanges Implementing: Simultaneously launched by the National Stock Exchange (NSE) and BSE.
• Implementation Date: Effective from August 3, 2026.
• Aim: To curb end-of-day price manipulation, improve price discovery, align Indian equity markets with global best practices, and deliver more accurate benchmark values for mutual funds, ETFs, and derivatives settlement.
• Phase 1
• Transition & Reference Price (3:15 PM – 3:20 PM): Continuous trading ends for eligible F&O stocks at 3:15 PM.
• The system calculates a reference price based on the Volume-Weighted Average Price (VWAP) of trades between 3:00 PM and 3:15 PM, applying a strict ±3% price band.
• **Phase 2
• Order Entry Window (3**:20 PM – 3:30 PM): 3:20 PM – 3:25 PM: Market and limit orders can be placed, modified, or canceled.
• 3:25 PM – 3:30 PM: Only limit orders are accepted; market orders cannot be altered or canceled.