Pre-Open Auction Session: Meaning, Timings, How It Works
The Pre-Open Auction Session helps determine the opening price of stocks before regular trading begins. Under the revised framework effective September 7, 2026, the pre-open session in the cash equity segment will continue to operate as an auction, but its current single-window format will be reorganised into multiple phases to align the order-handling process with the Closing Auction Session (CAS).
The changes include separate windows for market and limit orders, a system-driven random close, and a dedicated order matching period. These changes are intended to make the opening auction more structured and improve price discovery, while the regular market opening time will remain unchanged at 9:15 A.M.
Key Takeaways
- The revised Pre-Open Auction Session framework will take effect in the cash equity segment from September 7, 2026.
- The new framework will align the pre-open order handling process with the Closing Auction Session (CAS).
- The first order entry phase will allow both market and limit orders, followed by a limit order-only phase.
- A system-driven random close will be introduced before order matching.
- Stop-loss and iceberg orders will not be allowed during the pre-open auction session.
- The revised process will include a dedicated 2-minute order matching phase.
- The Continuous Trading Session (CTS) will continue to begin at 9:15 A.M.
What Is the Pre-Open Auction Session
The Pre-Open Auction Session is a 15-minute session that runs from 9:00 A.M. to 9:15 A.M., during which the exchange collects buy and sell orders to determine a stock's opening price.
Instead of executing trades immediately, it calculates an equilibrium price, which is the price at which the maximum number of shares can be matched between buyers and sellers. This process helps ensure fair price discovery and reduces price volatility at market open.
From September 7, 2026, the Pre-Open Auction Session in the cash equity segment will follow a revised framework aligned with the Closing Auction Session (CAS). The existing single order entry window will be replaced with two phases.
Between 9:00 A.M. and 9:05 A.M., both limit and market orders can be placed. Between 9:05 A.M. and 9:10 A.M., only limit orders will be accepted, and the order entry window will close at a system-driven random time between 9:08 A.M. and 9:10 A.M.
After the random close, eligible orders are matched at the final equilibrium price. Market orders take priority, and any remaining market orders are matched against limit orders based on price-time priority. This is followed by the transition to the Continuous Trading Session (CTS), which begins at 9:15 A.M.
Order Rules During the Pre-Open Auction
Under the revised framework, both limit orders and market orders are considered while computing the equilibrium price. However, iceberg orders are not permitted, meaning the entire order quantity must be disclosed. Stop-loss orders are also not allowed during the pre-open auction.
Information Available During the Pre-open Session
During the Pre-Open session, the exchange will publish the following indicative information:
- Indicative equilibrium price of the stock
- Indicative cumulative buy and sell quantity of the stock
- Indicative imbalance quantity of the stock at the equilibrium price
- Indicative imbalance quantity based on market orders of the stock
- Indicative index
Stock exchanges may also disseminate additional relevant information during the session at their discretion.
Pre-Open Auction Session Timings
|
Session |
Particulars |
Start Time |
Duration |
|
1 |
Order entry period for both limit and market orders |
9:00 A.M. |
5 mins |
|
2 |
Order entry period for limit orders only. No modification/ cancellation allowed for market orders; random close in the last 2 mins |
9:05 A.M. |
5 mins |
|
3 |
Order matching |
9:10 A.M. |
2 mins |
|
4 |
Transition of orders from pre-open session to CTS |
9:12 A.M. |
3 mins |
Why Has the Pre-Open Auction Framework Been Revised?
The revised framework aligns the Pre-Open Auction Session with the Closing Auction Session (CAS) and creates a consistent auction mechanism across both market opening and closing.
The key objectives include:
- Introducing a separate order-entry window for market and limit orders.
- Reducing last-moment order manipulation through a system-driven random close.
- Standardising auction behaviour across opening and closing sessions.
- Improving transparency in opening price discovery.
Pre-Open Session: Existing vs Revised Framework
|
Feature |
Existing Framework |
Revised Framework (Effective September 7, 2026) |
|
Order Entry |
All orders, including market, limit and stop-loss orders, are allowed in a single window from 9:00 A.M. to 9:07 A.M. |
Order entry is split into two phases.
|
|
Random Close |
The order entry session ends at a fixed time of 9:07 A.M. |
Order entry closes at a system-driven random time during the last two minutes, anytime between 9:08 A.M. and 9:10 A.M. |
|
Order Matching |
Order matching takes place around 9:07 A.M. to 9:08 A.M. |
A dedicated two-minute order matching window runs from 9:10 A.M. to 9:12 A.M. |
|
Transition to CTS |
Orders transition towards CTS before the market opens. |
Orders transition from the Pre-Open session to CTS between 9:12 A.M. and 9:15 A.M. |
|
Market Open (CTS) |
The Continuous Trading Session begins at 9:15 A.M. |
The Continuous Trading Session continues to begin at 9:15 A.M., unchanged. |
Conclusion
The revised Pre-Open Auction Session introduces a more structured process for determining the opening price of stocks in the cash equity segment. By separating market and limit order entry, introducing a system-driven random close and adding a dedicated order matching period, the new framework aims to improve price discovery and align the opening auction more closely with the Closing Auction Session.
For investors, the key changes include separate order entry windows, restrictions on certain order types and the random closure of order entry. The regular Continuous Trading Session (CTS) will continue to begin at 9:15 A.M.