SEBI's new auction system is changing how stocks close
SEBI is rolling out a Closing Auction Session (CAS) for stocks, but the change will be phased — it will initially apply only to cash-market stocks that have derivative contracts, while the existing VWAP-based (last-30-minute) method will continue to apply for other stocks.
Starting August 3, 2026, for cash-market stocks that have derivative contracts, this new system is designed to make closing prices more accurate and less jumpy.
What's actually changing?
The CAS runs from 3:15pm to 3:35pm in four quick phases.
First, it sets a starting price using recent trades.
Then, traders can place orders—market and limit orders are allowed initially, then only limit orders—until a random close between 3:28 and 3:30pm.
After that, orders are matched at an "equilibrium" price that maximizes executable volume, though some orders may remain unexecuted, and the price aims to be as fair as possible.
Why does it matter?
This should mean clearer and more honest closing prices for things like indices and mutual funds.
By gathering all the action into one session, it gets harder for anyone to mess with prices at the last minute—and passive investors get a better deal too.