The Securities and Exchange Board of India (SEBI) introduced the Periodic Call Auction mechanism in 2013 to address the issue of volatility and price manipulation in illiquid stocks.

Here's a brief overview of how it works and its key criteria:

• To enhance transparency, reduce volatility, and curb manipulation in stocks with low liquidity.
• To provide a fair and efficient price discovery mechanism for such securities.

A stock may be classified as illiquid if:

1. Average daily number of trades is less than 50 in a rolling quarter.
2. Average daily trading volume is less than ₹10 lakh (or ₹1 million).
3. Not classified as “illiquid” if it is part of any index (e.g., Sensex, Nifty) or has derivatives contracts.
4. These parameters are reviewed quarterly.

There are six call auction sessions run in a day that starts from 9.30 AM of 1 hour each. The window of call auction for trading is like the pre-market session conducted for equity stocks. During this session, 0 might be displayed in the bids and offers, as the market orders are initially priced at 0 in the pre-market session.

Also, there is a 45-minute window provided for order placement, specific modifications, and cancellation. Note that all the orders are accepted and matched in the next 8 minutes, and trades are confirmed. Also, there will be a 7-minute buffer period before the subsequent call auction session begins.

Session Number	Start Time - Order Placement	Order Matching	Buffer Period
1	9:30 AM - 10:15 AM	10:15 AM - 10:23 AM	10:24 AM - 10:30 AM
2	10:30 AM - 11:15 AM	11:15 AM - 11:23 AM	11:24 AM - 11:30 AM
3	11:30 AM - 12:15 PM	12:15 PM - 12:23 PM	12:24 PM - 12:30 PM
4	12:30 PM - 1:15 PM	1:15 PM - 1:23 PM	1:24 PM - 1:30 PM
5	1:30 PM - 2:15 PM	2:15 PM - 2:23 PM	2:24 PM - 2:30 PM
6	2:30 PM - 3:15 PM	3:15 PM - 3:23 PM	3:24 PM - 3:30 PM

If you intend to buy/sell illiquid stocks that are on periodic call auction, you would be required to place your orders in the first 45 minutes. Note that you can buy/sell on the basis of your order if it matches in the next 8 minutes.

Please Note

• If the order is placed but not executed during a session, it will be retried for execution in the following sessions throughout the day.
• IOC (Immediate or Cancel) and GTT orders will be rejected even if triggered for stocks under periodic call auction category.
• AMOs is not allowed for stocks under periodic call auction category.