Market-on-Open / Market-on-Close (MOO/MOC)
Auction orders that execute at the official opening (MOO) or closing (MOC) price — guaranteeing the auction print but not a specific price.
Market-on-open (MOO) and market-on-close (MOC) orders are non-limit orders held by the exchange and executed in its official opening or closing auction at the single auction-determined price. You are guaranteed to participate in the auction print, but you accept whatever price the auction sets — execution is certain, price is not.
These auctions concentrate enormous liquidity at one price, which is why they exist. Index funds and ETFs trade MOC to match benchmarks calculated on closing prices, and rebalancing or index-reconstitution dates produce huge, predictable closing flow. Limit-on-open (LOO) and limit-on-close (LOC) variants add a price cap for traders unwilling to take the raw auction print.
Mechanics are deadline-driven: NYSE accepts MOC entry until 3:50 PM ET while Nasdaq's cutoff is 3:55 PM ET (both publish imbalance feeds in the final minutes that traders lean on or fade), while MOO orders feed the opening auction shortly after the 9:30 bell. Miss the cutoff and the order is rejected; large imbalances can move a stock meaningfully into the auction.
Related Terms
Execution
The process of completing a trade — from order submission through matching and confirmation. Execution quality affects real-world returns.
BeginnerLiquidity
How easily you can enter or exit a position without moving the price. High liquidity = tight spreads, deep order books, fast fills.
BeginnerMarket Order
An order to buy or sell immediately at the best available price. Guarantees execution but not the fill price.
BeginnerMarket-on-Close (MOC) Order
A market order that executes in the official closing auction at the day's closing price. Used to guarantee a close print; large MOC imbalances can move price into the bell.
Intermediate