What is Closing Auction Session?
What is Closing Auction Session?

Closing auction, which allows execution at the closing price, is a trading mechanism commonly used in securities markets across the globe.  During a closing auction, market participants interested in trading at the closing price may input buy and sell orders.  Then their orders interact with each other to form a consensus closing price for each security and orders are executed at that price.

CAS commences immediately after the completion of the Continuous Trading Session (“CTS”).

CAS would last for about 8 to 10 minutes and consists of a Reference Price fixing period, an order input period, a no-cancellation period and a random closing period as follows:

 Full Day TradingHalf Day Trading*
Reference Price Fixing Period16:00 – 16:0112:00 – 12:01
Order Input Period16:01 – 16:0612:01 – 12:06
No-Cancellation Period16:06 – 16:0812:06 – 12:08
Random Closing Period16:08 – 16:1012:08 – 12:10

* Eves of Christmas, New Year and Lunar New Year


  • In the first period (Reference Price Fixing Period, 4:00-4:01 pm), a Reference Price, which sets the allowable price limit of CAS (±5 per cent from the Reference Price), is calculated for each CAS Security.  The Reference Price is determined by taking the median of 5 nominal prices in the last minute of the CTS and the system would take 5 snapshots on the nominal prices at 15-second interval starting from 15:59:00.
  • In the second period (Order Input Period, 4:01-4:06 pm), at-auction orders and at-auction limit orders within the ±5 per cent price limit could be entered, amended or cancelled on CAS Securities.
  • Starting from the third period (No-Cancellation Period, 4:06-4:08 pm), at-auction orders and at-auction limit orders could be entered.  However, the prices of new at-auction limit orders must be between the lowest ask and highest bid of the order book, and no orders could be amended or cancelled. 
  • In the last period (Random Closing Period, 4:08-4:10 pm), the order rules from the No-Cancellation period apply and the market closes randomly within two minutes. 
  •  After the random closing period, there is order matching for all CAS Securities at the final IEP.  In cases where no final IEP is established during CAS, the Reference Price would be treated as the final IEP for order matching and would become the closing price of the CAS Security.  This price would also be used for order matching based on matching priority, i.e. by order type, price and then time.

What securities are covered under CAS?

CAS covers all equities (including depository receipts, investment companies, preference shares and stapled securities), funds (including Exchange Traded Funds (ETFs) and REITs) and leveraged and inverse products (L&I Products).

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