India's Stock Market Adopts New End-of-Day Trading Timelines and Closing Price Mechanism

India’s stock market splits into three end-of-day timelines from Monday, changing both when different securities stop trading and how the closing prices of stocks with futures and options (F&O) contracts are determined.

Continuous trading in F&O-linked stocks will end at 3:15 p.m. before they move into a Closing Auction Session, or CAS. Other stocks will continue trading until 3:30 p.m., while index and stock derivatives will remain open until 3:40 p.m.

The critical distinction for investors is that stocks covered by CAS do not shut for the day at 3:15 p.m. Only continuous trading ends at that point. A 20-minute auction process then runs until 3:35 p.m. to determine the official closing price.

The change marks a fundamental departure from India’s existing closing price mechanism. Currently, the closing price of a stock is calculated using the volume-weighted average price, or VWAP, of trades executed during the final 30 minutes of continuous trading.

Under the new system, buy and sell orders for eligible stocks will be pooled during the auction and matched at a single equilibrium price. In the first phase, CAS will apply only to stocks on which derivative contracts are available. Other securities will continue to use the existing 30-minute VWAP methodology, according to a SEBI circular.

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The closing price is a crucial market benchmark as it is used to calculate indices such as the Nifty and Sensex, determine mutual fund net asset values, settle derivative contracts on expiry, value pledged securities and calculate portfolio profit and loss.

What happens after 3:15 p.m.?

Between 3 p.m. and 3:15 p.m., exchanges will calculate the VWAP of trades in each eligible stock. That figure will become the reference price for the closing auction.

At 3:15 p.m., continuous trading in these stocks will stop and the market will transition to CAS. No orders can be entered during the five-minute transition period ending at 3:20 p.m.

Open limit orders from the continuous session will generally be carried into the auction. Stop loss orders, iceberg orders and orders outside the permitted CAS price band will not be carried forward. The auction’s price band will be set at 3% above or below the reference price.

From 3:20 p.m. to 3:25 p.m., investors can place both market and limit orders. Exchanges will disseminate information including the indicative equilibrium price, cumulative buy and sell quantities, order imbalances and indicative index values.

Between 3:25 p.m. and 3:30 p.m., only limit orders can be placed. Market orders entered earlier cannot be modified or cancelled during this period.

The order entry window will close randomly between 3:28 p.m. and 3:30 p.m. The system driven random close is intended to discourage a last minute rush of orders.

From 3:30 p.m. to 3:35 p.m., exchanges will stop accepting orders and run the matching process. All eligible trades will then be executed at the equilibrium price, which will become the stock’s official closing price.

How will the closing price be decided?

The equilibrium price will be the price at which the largest volume of shares can be executed.

If more than one price produces the same executable volume, the price with the smallest unmatched order quantity will be selected. If there is still a tie, the price closest to the reference price will become the closing price. If no equilibrium price is discovered, the reference price itself will be used.

Market orders will receive priority over limit orders. Eligible market orders will first be matched with other market orders based on time priority. Residual market orders will then be matched with limit orders, followed by the matching of remaining eligible limit orders using price-time priority.

Unlike continuous trading, orders submitted during CAS will not be executed immediately. They will remain pooled until the auction closes, after which all successful orders will be transacted at the same equilibrium price, according to Zerodha.

Why is SEBI changing the system?

The auction is designed to concentrate liquidity at the close, improve the execution of large orders and produce a price reflecting the combined demand and supply of market participants.

Passive funds tracking indices frequently need to execute substantial orders near the end of a session to replicate closing prices. Those transactions can move prices while being executed and increase tracking error. Pooling orders into a single auction may allow large buyers and sellers to transact more efficiently at the same price.

The framework is also intended to make it harder for large orders placed in the final minutes to disproportionately influence stock and index closing levels.

Closing auctions are already used in major global markets, including the New York Stock Exchange and the London Stock Exchange.

What changes for intraday traders?

For traders using the MIS intraday product, the auto square-off time for stocks covered by CAS will move to 3:10 p.m. Stocks outside CAS will have an auto square-off time of 3:25 p.m., while the timing for index and stock derivatives will also be 3:25 p.m.

Futures and options themselves will not enter the closing auction. They will continue trading normally until 3:40 p.m., even as their underlying stocks move from continuous trading into CAS after 3:15 p.m.

A post-close cash market session will operate between 3:50 p.m. and 4 p.m., during which trades will be executed at the closing price determined earlier.