Closing Auction
Market Microstructure glossary · Market Microstructure Fundamentals
Definition
A call auction conducted at the end of the trading day to establish a closing price. Increasingly important as benchmark for index funds, derivatives settlement, and performance measurement.
Closing Auction in plain English
During most of the day, buyers and sellers trade one small batch at a time, so the 'price' is really just wherever the last trade happened to land. A closing auction fixes that: at the very end of the day, the exchange collects ALL the buy and sell orders at once and finds the single price that lets the most shares trade, and that becomes the official closing price. This matters because huge amounts of money quietly ride on that one number — index funds that must own stocks in exact proportions, contracts that pay out based on it, and reports that grade how well a fund did all use the close, so everyone wants it set fairly with lots of orders in one pool rather than by one random last trade.
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