The National Stock Exchange (NSE) announced on Thursday the introduction of updated rules for its preliminary auction session, which will take effect on September 7, 2026. The goal of the changes is to align the process with the Closed Auction Session (CAS).
According to an NSE announcement on the social network X, the total duration of the preliminary session will remain the same—15 minutes, from 9:00 to 9:15 AM. However, the exchange will divide this session into separate stages for order submission, matching, and transition to continuous trading.
Under the new schedule, investors will be able to place both market and limit orders from 9:00 to 9:05 AM. Then, from 9:05 to 9:10 AM, the exchange will accept only limit orders. This stage will have a random closure within the last two minutes.
Order matching will occur from 9:10 to 9:12 AM. The following three minutes, until 9:15 AM, will be used to transfer orders from the preliminary session to the Continuous Trading Session (CTS).
The revised mechanism also defines the order of trade execution. Market orders matched with other market orders will receive the highest priority based on time priority. Any remaining market orders will then be matched with limit orders using price and time priority. In the final stage, remaining limit orders will be matched with other limit orders also based on price and time priority.
This step brings the preliminary auction process in line with the CAS framework, ensuring a more consistent auction structure around price determination at the beginning and end of the trading day.