What Is a Periodic Call Auction? Illiquid Scrips

A periodic call auction is the trading mode Indian exchanges apply to securities they classify as illiquid. Instead of continuous order matching through the day, orders in these scrips collect over a window and are matched in a single batch at one price. NSE runs six such sessions of one hour each, from 9:30 am to 3:30 pm, and a security in the periodic call auction session is not available in the continuous market at the same time.

Why does a periodic call auction exist at all?

Thin order books are easy to move. In a security that trades a few thousand rupees a day, a small order can print a large price change, and that price then becomes the reference for everything downstream. Batching orders into a single matched price at fixed intervals concentrates whatever liquidity exists into one moment instead of scattering it, and removes the ability to walk a book that is nearly empty.

SEBI introduced the mechanism for illiquid scrips in February 2013 and rationalised the criteria later that year. NSE implemented it from 8 April 2013.

Which securities get moved into it

The current test is turnover based. Under SEBI circular CIR/MRD/DP/38/2013 dated 19 December 2013, a security is illiquid if both of the following hold:

• Average daily turnover of less than 2 lakh rupees, calculated over the previous two quarters.
• The scrip is classified as illiquid at all exchanges where it is traded.

Average daily turnover is daily trading turnover divided by the total number of available trading days in a month, including special trading days. Turnover counts trades in the EQ, BE, BT, IL and BL series, and securities that were available for trading but did not trade are still counted.

That test replaced the original 2013 criteria, which looked at average daily trading volume below 10,000 and average daily trades below 50.

Several categories are carved out before the list is drawn up: securities that commenced trading during the quarter, exchange traded funds and mutual funds, securities with derivative products or trading at no price band, and equity-linked securities such as partly paid-up shares, convertible warrants, DVRs, debt instruments and preference shares.

How the sessions run

The random closure matters. Because the exact end of order entry is not knowable in advance, an order cannot be timed to land at the last possible instant, which is the behaviour a call auction is designed to discourage.

If an index-based market-wide circuit break triggers during order collection, the session is cancelled and orders are purged. If it triggers during matching, the match completes and the auction resumes at the next session after the normal market restarts.

Getting in and out of the list

The list of common illiquid scrips is prepared on the fourth working trading day of the quarter in coordination with the other exchanges, published the same day, and takes effect on the second working Monday of the quarter. Market participants get at least two trading days of notice.

Exit needs two things at once: the scrip must have been in periodic call auction for at least two quarters, and it must no longer meet the illiquidity criteria. Separate exclusion criteria also lift a scrip out, including average market capitalisation above 10 crore rupees, dividends in at least two of the last three years, or profitability in at least two of the last three years combined with no more than 20 percent of promoter shareholding pledged and a book value at least three times face value.

Securities already at GSM Stage III or IV, or under ASM IBC Stage I or II during the review period, are exempt from shortlisting for the auction session.

Reading a call-auction stock

A periodic call auction is a statement about turnover, not about the company's ownership. The filings still tell you who holds the stock: the quarterly shareholding pattern, any promoter pledge disclosure, and insider trading disclosures when designated persons trade. The auction also stacks with other surveillance actions: a scrip at ESM Stage II carries a 2 percent band and a periodic call auction together, as set out in the ESM framework and alongside trade for trade settlement.

Flock reports those filings with their dates and source links. What a thin tape means for your own position is your call to make. Not investment advice.