SEBI Revises CAS Rules to change the stock market’s closing auction timings, order-handling procedures and the method used to calculate settlement prices for futures and options (F&O) contracts on expiry days.
The Securities and Exchange Board of India announced the revised framework on October 15, 2026, with most changes scheduled to take effect on December 7.
The changes follow a review of the Closing Auction Session (CAS), which was introduced to improve price discovery for shares at the end of the trading day.
The revised framework also restores the earlier volume-weighted average price method for determining expiry-day settlement prices for stock and index derivatives.
For traders and investors, the revised rules matter because closing prices can influence derivative settlements and the handling of orders near the end of the trading session.
The changes also affect how eligible orders move from regular trading into the closing auction.
SEBI Revises CAS Rules and Market Timings
Under the revised framework, the Closing Auction Session will run from 3:30 pm to 3:40 pm, shifting the auction window later in the trading day.
The change is intended to improve the functioning of the closing process and the determination of closing prices.
The revised framework also changes how orders are handled as the regular continuous trading session ends.
Eligible unexecuted limit orders can be carried forward to the auction, subject to the prescribed conditions and applicable price bands.
Iceberg orders, which allow large orders to be displayed in smaller portions, will follow specific transition rules.
Eligible unexecuted iceberg orders may be converted into fully disclosed limit orders when transferred to the auction, unless the trader opts out when placing the order.
Stop-loss orders and orders outside the applicable price bands are subject to separate treatment.
Traders should check their broker’s instructions and the exchange’s implementation details before relying on the revised order-handling process.
F&O Settlement Method Returns to 30-Minute VWAP
One of the key changes concerns how stock and index derivatives are settled on expiry days.
SEBI has decided to restore the volume-weighted average price (VWAP) of the underlying securities during the final 30 minutes of the regular trading session as the basis for calculating expiry-day settlement prices.
VWAP calculates an average price by accounting for the volume traded at different prices.
Using the final 30-minute trading window means settlement prices will be based on trades completed during regular market activity rather than relying on the closing auction price under the earlier framework.
This is relevant to traders holding futures and options positions close to expiry.
The settlement price determines the value used to settle eligible derivative contracts, so changes in the calculation method can affect the final settlement outcome.
However, the revised methodology does not guarantee a profit or prevent losses. Actual outcomes continue to depend on market movements, contract positions and the prices of the underlying securities.
What the New Rules Mean for Traders and Investors
The revised CAS framework changes the timing and treatment of orders near the market close.
Traders who place orders late in the session should understand which orders may carry forward, which may be excluded and how applicable price bands and margin requirements operate.
The settlement formula is particularly important for F&O participants whose contracts expire on a given trading day.
Restoring the 30-minute VWAP method changes the reference used for expiry settlement, although it does not eliminate market risk or guarantee more favourable prices.
Long-term investors who primarily buy and hold shares may be less directly affected by the derivatives settlement change.
However, the closing auction can still matter when they place eligible orders near the end of the trading day.
Investors should distinguish between the closing price of a share, the price determined through the closing auction and the settlement price used for derivatives.
These concepts are related but serve different purposes in the market.
When Will the Revised SEBI Framework Take Effect?
The new framework is scheduled to take effect on December 7, 2026. Market participants and intermediaries will need to follow the revised requirements once implementation begins.
Stock exchanges and clearing corporations have been directed to update their operating procedures in line with the revised rules.
Brokers may also communicate changes to order placement and settlement processes to their customers.
Traders should monitor official exchange circulars and broker notifications as the implementation date approaches.
Reviewing these details can help them understand how orders will be handled during the closing auction and how expiry-day derivative settlement prices will be determined.
