The pre-open session is the 15 minute window from 9:00 am to 9:15 am in which NSE and BSE collect orders and then match them at a single opening price before normal trading starts. Since 7 September 2026, market orders are accepted only until 9:05 am, limit orders until the window closes at a random moment between 9:08 and 9:10, and matching runs from 9:10 to 9:12. Since December 2025, index and stock futures have a pre-open session too.
The pre-open session, also called the pre-market session or opening call auction, exists to find a fair opening price. Overnight news and large institutional orders all land at once in the morning. Instead of letting the first trade set the price, the exchange collects every order and finds the level at which the largest quantity can trade. That becomes the opening price, and the Nifty 50 and Sensex opening values are built from those prices.
The three phases
Order entry runs from 9:00 to 9:10. In the first five minutes, traders can place, change or cancel both market and limit orders. From 9:05, only limit orders are accepted and any market order is rejected. The exchange ends order entry at a random point between 9:08 and 9:10 so that nobody can time the last second. Matching then runs from 9:10 to 9:12, and a short buffer carries the market into the normal session at 9:15.
How the opening price is found
The system tests every price at which buy and sell orders overlap and picks the one that clears the most shares. If two prices tie, it chooses the one closer to the previous close. Orders that do not match are carried into the normal session. Limit orders keep their price, and market orders carried forward are converted to limit orders at the opening price.
Pre-open in futures
From 8 December 2025, NSE runs the same session for current month index and single stock futures, and for next month contracts in the last five days before expiry. The order entry rules match the equity segment. Stop loss and immediate-or-cancel orders are not accepted in this window.
A worked example
Suppose a stock closed at ₹500 on Tuesday and strong results come out overnight. By 9:08 on Wednesday, buy orders are stacked between ₹520 and ₹540 and sell orders between ₹515 and ₹545. The system finds that ₹528 clears the largest number of shares, so ₹528 is the opening price. A trader who placed a market buy at 9:03 is filled at ₹528, not at the ₹545 the first seller asked for.
Why it matters to a SAHI trader
The indicative price shown during the window can move a lot in the last two minutes, and limit orders are the only way in after 9:05. Compare the indicative Nifty open with GIFT Nifty to judge whether the gap is likely to hold. The closing auction session uses the same call auction logic at the end of the day.
FAQs
Can I cancel a pre-open order?
Yes, until order entry closes. After the random close between 9:08 and 9:10, nothing can be changed.
Is every stock traded in the pre-open session?
All equity shares on NSE and BSE take part. Options do not have a pre-open session.
Why does the indicative price keep changing?
It is recalculated with every new, changed or cancelled order, so it settles only when order entry closes.
Does the pre-open session apply on Muhurat trading day?
Yes. The Diwali session includes a short special pre-open window before its normal market period.