What is a Market-on-Close (MOC) Order? Definition, Formula, and Example
A Market-on-Close (MOC) order is a market order that executes at the final closing price of the trading day, regardless of that price's level.
What is a Market-on-Close (MOC) Order?
A Market-on-Close (MOC) order is a market order that executes exclusively at the market's official closing auction price, regardless of what that final price is. Traders use MOC orders to guarantee participation in the end-of-day liquidity pool without specifying a price limit. Unlike continuous intraday market orders that execute against the order book instantly, MOC orders remain dormant until the closing auction mechanism aggregates all buy and sell imbalances to determine a single clearing price. This order type is the primary mechanism for institutional funds tracking daily closing benchmarks and retail traders seeking immediate end-of-day liquidity.
How it's calculated / identified
MOC orders do not require a mathematical calculation by the trader, but they dictate the exchange's closing auction matching logic. When a trader submits an MOC order, it enters a dedicated closing-order queue. At 3:50 PM EST, exchanges stop accepting MOC orders. At 4:00 PM EST, continuous trading halts. The exchange then aggregates all MOC buy orders and MOC sell orders, alongside continuous order book imbalances, to find a single clearing price.
The exchange calculates the price that maximizes the volume of executable shares. All MOC orders execute at this single clearing price. If there is a severe imbalance, the exchange may publish a closing price indication to attract liquidity, but the MOC order remains unpriced and will execute at the final determined level.
Worked example
Assume an institutional fund needs to liquidate 50,000 shares of NVDA at the end of the day. NVDA is trading at $850.00 at 3:45 PM. The fund submits an MOC order to sell 50,000 shares.
At 3:50 PM, the exchange locks the MOC book. At 4:00 PM, continuous trading stops. The exchange aggregates the total MOC sell volume and compares it to the total MOC buy volume. If a massive sell imbalance exists, the exchange matches the orders at a lower clearing price, say $848.50. The fund's 50,000 shares execute at exactly $848.50, regardless of where the stock traded intraday.
When traders use it
Traders use MOC orders to guarantee end-of-day execution without price constraints. Mutual funds and ETFs use MOC orders heavily to execute daily creations and redemptions at the official Net Asset Value (NAV) closing price. Retail swing traders use MOC orders to exit positions on the exact day they trigger a signal, ensuring they capture the closing candle. MOC orders are also used by statistical arbitrage funds to pair long and short legs of a trade at the close, neutralizing overnight gap risk.
Limitations / common misconceptions
The primary limitation of an MOC order is absolute price exposure. Because it is an unpriced market order, a sudden late-day imbalance can push the closing price significantly away from the 3:59 PM trading price, resulting in severe slippage. Traders often mistakenly believe MOC orders execute at 3:59 PM; they execute solely at the 4:00 PM auction print. Furthermore, exchanges restrict MOC order modifications and cancellations after 3:50 PM to prevent manipulation of the closing auction, meaning traders cannot pull their orders once the cutoff passes.