The Securities and Exchange Board of India (SEBI) has directed all recognised stock exchanges and clearing corporations to implement a Closing Auction Session (CAS) in the equity cash segment, effective August 3, 2026. This regulatory shift replaces the current Volume Weighted Average Price (VWAP) mechanism used during the last 30 minutes of the Continuous Trading Session (CTS) with a structured auction process. The decision, issued via circular HO/47/11/11(3)2025-MRD-POD2/I/2765/2026 on January 16, 2026, aims to align Indian markets with global best practices by aggregating market interest into a single liquidity pool. This change is critical for investors as the closing price serves as the reference point for derivatives settlement, index computation, and mutual fund net asset value (NAV) determination.

Implementation Framework

Initially, the CAS will apply only to stocks in the cash segment where derivative contracts are available. For these securities, the closing price will be determined through an equilibrium price mechanism rather than the trailing 30-minute VWAP. The remaining securities in the cash segment will continue to use the VWAP method. SEBI’s Secondary Market Advisory Committee deliberated on this framework after receiving public comments on consultation papers dated December 5, 2024, and August 22, 2025, alongside feedback from stock exchanges, clearing corporations, mutual funds, and Foreign Portfolio Investors (FPIs).

The CAS is structured as a separate 20-minute session from 3:15 pm to 3:35 pm on all trading days. The session is divided into four distinct phases to ensure orderly price discovery:

The order entry session will close randomly between 3:28 pm and 3:30 pm, driven by system algorithms to prevent gaming of the close. Following this, the equity derivatives segment will continue operating until 3:40 pm, while the post-close session in the cash segment will run from 3:50 pm to 4:00 pm, executing trades at the discovered closing price.

Operational Mechanics and Price Discovery

The reference price for the CAS will be based on the VWAP of trades executed between 3:00 pm and 3:15 pm. If no trades occur in this window, the Last Traded Price (LTP) of the day will serve as the reference; if no trades occur all day, the previous day’s closing price will be used. A strict price band of +/- 3% from the reference price will apply during the CAS. To maintain alignment, the price band for stock futures between 3:15 pm and 3:40 pm will also be fixed at +/- 3%, suspending the existing dynamic flexing framework for stock futures during this period.

Only limit and market orders are permitted in the CAS; iceberg and stop-loss orders are prohibited. Market orders will take priority over limit orders in execution. Unexecuted limit orders from the CTS will carry forward to the CAS, except for stop-loss and iceberg orders or those outside the price band. These carried-forward orders will enjoy higher time priority than new orders placed during the CAS. If no equilibrium price is discovered, the reference price itself will become the closing price.

Pre-Open Session Alignment and Next Steps

To ensure consistency across market open and close mechanisms, SEBI is simultaneously modifying the Pre-Open Auction Session framework, effective September 7, 2026. The pre-open session will now run from 9:00 am to 9:15 am, featuring a random close between 9:08 am and 9:10 am, mirroring the randomness introduced in the closing auction. Both market and limit orders will be allowed, with market orders given execution priority.

Stock exchanges and clearing corporations must jointly formulate Standard Operating Procedures (SOPs) within 30 days of the circular date to address price band alignment for stock futures and settlement price calculations for derivatives. They are also required to amend relevant bye-laws and strengthen market surveillance systems to monitor integrity concerns during the new CAS windows. This directive is issued under Section 11(1) of the Securities and Exchange Board of India Act, 1992, and Regulation 51 of the Securities Contracts (Regulation) (Stock Exchanges and Clearing Corporations) Regulations, 2018.

What the Numbers Show

The shift from a continuous 30-minute VWAP to a consolidated 20-minute auction represents a significant structural change in price discovery. By restricting order types to limit and market orders and introducing a random close, SEBI aims to mitigate end-of-day volatility manipulation often associated with continuous trading near the bell. The alignment of stock futures price bands with the cash segment’s CAS price band (+/- 3%) removes the previous dynamic flexing mechanism during this critical window, potentially reducing arbitrage opportunities that relied on divergent price bands. For passive funds, the aggregation of liquidity into a single equilibrium price is expected to lower tracking errors, as they can transact larger blocks at a single consensus price rather than slicing orders across the volatile final 30 minutes of continuous trading.