The pre-open market session in India starts 15 minutes before the regular market opening and lasts for 15 minutes. This session is also known as the pre-open call auction.
During the pre-open session, buy and sell orders are collected by the exchanges but no trades are executed. The orders are just queued.
A uniform opening price is calculated for each stock based on the buy and sell orders received. This is called the equilibrium price and it balances out demand and supply.
Once the regular market opens after the pre-open session, trading begins for each stock at its equilibrium price calculated during the pre-open.All buy and sell orders received during the pre-open are executed at the opening price. New orders are also allowed once the market opens.
Pre-open session helps discovery of the opening price more efficiently through an auction process. It ensures a smooth transition from pre-open to the regular trading session.
Pre-open trading helps reduce huge volatility in prices once the market opens compared to earlier when buy and sell orders would get piled up overnight.
Overall, the pre-open mechanism facilitates price discovery and ensures a more efficient market open in India. It helps reduce anomalies in pricing and provides a smooth start to trading.