A Pre-Open Session is a 15-minute window before the regular market opens during which traders can place, modify, or cancel their orders. Instead of executing immediately, the exchange collects all Buy and Sell orders and uses them to determine a fair opening price for the day.

This system helps reduce volatility, improves price discovery, and ensures a smoother transition into regular trading.

Pre-Open Sessions happen in the following segments:

• Equity (Cash) Segment
• F&O Segment (Futures)

Pre-Open Session Timings (Cash & F&O)

Session	Time	Action
Order Entry Period	9:00 AM - 9:07 AM	Traders can place, modify, or cancel orders.
Order Matching & Confirmation period	9:08 AM - 9:12 AM	Both Limit and Market orders are allowed, but special orders like Stop-loss are not.
Buffer Period	9:12 AM - 9:15 AM	The system matches Buy and Sell orders to determine a single opening price.

Which Instruments Participate in Pre-Open?

Eligible:

• Equity
• Current Month Futures (stock & index futures)
• Next Month Futures (only in the last 5 trading days of the month)

Not eligible (open directly at 9:15 AM):

• Options
• ETFs
• Spread Contracts
• Far-month Futures
• Futures under corporate action (merger, demerger, etc.) on that day

How Is the Opening Price Decided?

The exchange decides the opening price using “equilibrium price discovery,” based on:

1. Price at which maximum Buy–Sell orders match

2. The fewest unmatched orders

3. If tied, the price closest to the previous day’s close

If no match is found pre-open, the first trade at 9:15 AM becomes the opening price.

What Happens to Unmatched Orders?

• Limit orders: Move to the regular market session.
• Market orders: Converted to limit orders at the discovered opening price.

If no opening price is discovered, market orders move using the previous day’s closing price.