Important changes are set to take place in the way trading works and closing prices are determined in the Indian stock market. Market regulator SEBI is taking steps to improve transparency, strengthen price discovery and provide investors with a more reliable trading system.
In this direction, SEBI has revised the rules for the Closing Auction Session (CAS). The new framework introduces changes to trading timings, order types and the settlement process for derivatives. These changes will affect both the cash market and the futures and options (F&O) segment.
Let us look at SEBI’s revised closing auction rules and understand how they could affect traders, investors and the Indian stock market.
What’s Happening?
SEBI issued the revised framework for the Closing Auction Session (CAS) on 15 October 2026. It introduces changes to how closing prices are determined, how orders are placed and when derivatives trading ends. The new rules will come into effect from 7 December 2026, while some provisions related to pending orders will take effect from 8 February 2027.
CAS is a special trading session used to determine the final share price for the day. It aims to ensure a more transparent and reliable closing price, particularly when large trades take place towards the end of the trading day. CAS was initially introduced on 3 August for shares linked to futures and options. However, concerns over limited participation and sudden price volatility during expiry led to a review of the framework. Before issuing the revised rules, SEBI received more than 20,000 suggestions during the consultation process.
New Timing of the Closing Auction and Order Rules
Under the new framework, CAS will run from 3:30 pm to 3:40 pm. The reference price calculation and transition process will take place from 3:30 pm to 3:31 pm. From 3:31 pm to 3:36 pm, investors will be able to place both limit and market orders. After 3:36 pm, only limit orders will be allowed. Order entry will close at a random time between 3:38 pm and 3:40 pm.
SEBI has prohibited new stop-loss and iceberg orders during CAS. However, eligible pending limit orders from the continuous trading session will be carried forward to CAS. Pending iceberg orders will also be converted into limit orders displaying the full quantity, unless investors choose not to carry them forward.
These changes aim to make the order book more transparent and reduce the potential impact of sudden large orders on the closing price.
What Will Change in Derivatives Trading and Settlement?
SEBI has decided to retain the existing 30-minute volume-weighted average price (VWAP) method for settling F&O contracts on expiry. This means index derivatives will be settled using the index value derived from the VWAP of the underlying shares during the final 30 minutes of trading. For stock derivatives, the VWAP of the relevant share across all exchanges will be used.
On normal trading days, index derivatives trading will continue until 3:45 pm. However, on expiry days, trading in index contracts expiring that day will end at 3:30 pm. Trading in stock derivatives will continue until 3:45 pm, even on expiry days. Meanwhile, the post-close session in the cash market will run from 3:50 pm to 4:00 pm.
The CAS reference price will be calculated using the VWAP of the final 15 minutes. If no trades take place during this period, the last traded price of the day will be used.
What Does This Mean for Investors?
The revised rules could have the greatest impact on derivatives traders and investors who trade towards the end of the session. By retaining VWAP-based settlement, SEBI has kept the expiry settlement price separate from the final auction price determined through CAS. This could limit the direct impact of sudden volatility during the closing auction on derivatives settlement.
Following the announcement, shares of companies linked to the capital market showed a mixed trend on 16 October. In early trading, BSE was down around 0.8%, while Angel One had given up its initial gain of 2%. Meanwhile, Billionbrains Garage Ventures, the parent company of Groww, was trading around 2.5% higher.
Investors, particularly those who trade actively towards the end of the day, will need to understand the revised trading timings, order restrictions and expiry settlement process.
What’s Next?
SEBI’s revised CAS framework could make the process of determining closing prices in the Indian stock market more organised and transparent. Randomised order closure, the display of full quantities for eligible iceberg orders and VWAP-based settlement could help address concerns about potential price manipulation. However, the actual impact will depend on trading volumes, investor participation and market behaviour after the new rules take effect.
SEBI has directed stock exchanges and clearing corporations to update their standard operating procedures within seven days of the circular’s issuance. The success of the new framework will ultimately depend on whether it improves closing-price stability and makes the trading process more transparent.
Disclaimer: This article is for educational and informational purposes only and does not constitute investment advice or a recommendation to buy or sell any securities. The companies mentioned are cited as examples within the context of market developments. Investors are advised to conduct their own due diligence and consult their financial advisor before making any investment decisions.
Investments in the securities market are subject to market risks. Read all related documents carefully before investing.
