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• The trading day begins with a pre-open session from 9:00 a.m. to 9:30 a.m.

• At 9:30 a.m., an opening auction (opening cross/call auction) is triggered.

• After the auction, the market moves into continuous trading (from 9:31 a.m. onward) until the day closes at 3:00 p.m.

What Happens During Pre-Open

During the 9:00–9:30 a.m. window:

• Brokers (on behalf of clients) submit buy and sell orders — limit orders, market orders, etc. These feed into the electronic order book.

• Orders can also be modified or cancelled during this period.

• No trades are executed yet — orders only accumulate, awaiting the opening auction.

As orders come in, the system continuously recalculates a potential opening price based on the orders currently in the book.

Opening Auction — Price Discovery & Matching

At 9:30 a.m., the system determines the official “opening price” for each stock. The algorithm works roughly as follows:

1. It looks for the price at which the maximum number of shares can be traded (i.e., matching as many buy & sell orders as possible).

2. It tries to minimize the imbalance (i.e., leftover unmatched buy or sell orders). DocLib+1

3. Once that “equilibrium/auction price” is found, that price becomes the official opening price for the day.

• Orders that can match at that opening price are executed immediately — some orders may be filled, others partially, depending on volume.

• Orders that cannot match remain in the order book (for continuous trading once regular trading begins).

Why the Pre-Open & Auction Matter

• The process ensures a fair and transparent price discovery at the start of the trading day, reflecting the collective demand and supply before the opening bell.

• It helps avoid abrupt price swings/volatility by building a “clean slate” opening price based on real orders.

• It gives all participants, retail, institutional, and brokers, an equal opportunity to enter orders before the official open.

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