Opening and closing auction
Key points
- The aim is to prevent price formation through isolated, manipulable trades.
- The closing auction price matters because index funds and institutions use it as the valuation price; index composition changes generate heavy volume at the close.
- orders are not visible during a single-price auction (a "blind" period), so market orders may fill at unexpected prices.
Formula / calculation
the equilibrium price is where cumulative buy and sell quantities intersect, maximising matched lots. In a tie, the price that minimises leftover quantity and lies closest to the reference price is chosen.
Interpretation
The closing auction price matters because index funds and institutions use it as the valuation price; index composition changes generate heavy volume at the close. The gap between the opening price and the previous close is watched as a signal.
Pitfalls
orders are not visible during a single-price auction (a "blind" period), so market orders may fill at unexpected prices. Imbalanced orders in the closing auction can push the price away from intraday levels.
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Frequently asked questions
What is Opening and closing auction?
The opening and closing auctions are single-price periods where orders are collected for a set time and matched at one equilibrium price.
How is Opening and closing auction calculated?
the equilibrium price is where cumulative buy and sell quantities intersect, maximising matched lots. In a tie, the price that minimises leftover quantity and lies closest to the reference price is chosen.
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