What is a Market on Close (MOC) Order? Definition and Rules
A market on close (MOC) order is a limit order that executes at the official closing price of a stock, submitted during the closing auction window and subject to strict cut-off times and size limits.
What is a Market on Close (MOC) Order?
A market on close (MOC) order is an order type that guarantees execution at the official closing price of a stock on the primary exchange. The order enters the closing auction and fills at the single price that clears the maximum volume at the close. MOC orders remove the uncertainty of holding a position through the close, but they surrender price control entirely — the execution price is the closing print, whatever it happens to be.
How a MOC Order is Identified and Processed
The mechanics differ by exchange. On the NYSE, MOC orders must be entered by 3:45 p.m. ET (15 minutes before the close) and cannot be canceled after 3:58 p.m. ET. On the Nasdaq, the deadline is 3:50 p.m. ET for entry and 3:55 p.m. ET for cancellation. Orders entered after the deadline are rejected outright.
The exchange runs a closing auction at 4:00 p.m. ET. The system aggregates all MOC orders plus regular limit and market orders that rest in the book. The official closing price is the price at which the maximum number of shares can cross. All MOC orders fill at that single price. There is no bid-ask spread paid; the execution price is the auction price.
Exchanges impose size limits on MOC orders. On the NYSE, the limit is 500,000 shares or $2 million in value per order. Orders above these thresholds require an exchange official's approval before entry. The exchange publishes an imbalance indicator starting at 3:30 p.m. ET, showing whether buy or sell MOC interest dominates. This imbalance is a tradable signal — a large buy imbalance often pushes the closing price above the prevailing bid.
Worked Example: SPY
On a typical expiration Friday, SPY trades at $550.12 at 3:40 p.m. ET. A fund manager enters a MOC order to buy 100,000 shares. The exchange's imbalance feed shows a net buy imbalance of 250,000 shares across all MOC orders. At 4:00 p.m., the auction crosses at $550.35 — 23 cents above the last regular print. The manager's entire 100,000 shares fill at $550.35. The price moved in the manager's favor because the buy imbalance pushed the auction price up. Had the manager used a regular limit order at $550.12, the order would have gone unfilled.
When Traders Use MOC Orders
Index funds and ETFs use MOC orders to track the closing price precisely. The official close determines net asset value for mutual funds and settlement prices for index options and futures. A fund that needs to replicate the index return buys at the close to minimize tracking error.
Active traders use MOC orders to exit positions before overnight risk. A trader holding a momentum stock into a Federal Reserve announcement at 2:00 p.m. can hold the position through the announcement and exit at the close with a MOC order. The order guarantees a fill, eliminating the risk of a gap down at the open the next day.
Market makers and institutional desks watch the MOC imbalance feed as a short-term signal. A persistent buy imbalance into the close often indicates institutional accumulation. The imbalance itself moves the closing price, so traders position ahead of the auction to capture the move.
Limitations and Common Misconceptions
MOC orders do not protect against adverse price moves. The closing auction can gap sharply from the last regular trade. A stock trading at $100 at 3:59 p.m. can close at $95 if a wave of sell MOC orders hits the auction. The MOC order fills, but at a price far worse than the last visible quote.
MOC orders do not work for illiquid stocks. A stock with thin volume and a wide spread can have a closing auction with only a few hundred shares crossing. A large MOC order moves the closing price dramatically. The exchange's size limits exist precisely to prevent this.
MOC orders are not the same as limit-on-close (LOC) orders. A LOC order specifies a minimum price. If the auction price is worse than the limit, the LOC order does not fill. A MOC order always fills, regardless of price.