A Market-on-Close (MOC) order is a market order that is submitted to execute as close to the closing price as possible.

You want to sell 100 shares of XYZ at the best market price, and decide that the closing price for this stock has historically proven to be the best price of the day. You click the Bid price to create a SELL order, and select MKT CLS in the Type field to specify a market-on-close order. The word MARKET appears in the Lmt Price field to illustrate that you are willing to sell at the closing market price. (If the equity trades on NYSE or AMEX, you can route directly to the exchange. For other stocks, you must route through SMART, and IB will simulate the order by submitting it as close to the market’s closing time as possible.) Make sure the market doesn’t close in less than 15 minutes! Submit the order, which will execute at the closing market price.

Summary of NYSE rules for entering/canceling/modifying market-on-close (MOC)

• All MOC orders must be received at NYSE (and at AMEX) by 15:40 ET unless entered to offset a published imbalance.
  
  
• After 15:40 ET, you may only enter MOC orders on the contra side of the last imbalance published, regardless of size.

  Example: If the 15:50 ET published imbalance reverses the prior published imbalance, only orders that offset the 15:50 imbalance publication will be accepted.

• Exception: On expiration days, you cannot enter MOC orders after 15:40 ET to establish or liquidate positions related to a strategy involving derivative instruments, even if these orders would offset a published imbalance.
  
  
• New York Stock Exchange (NYSE) rules also prohibit the cancellation or reduction in size of any market-on-close (MOC) order after 15:40 ET.

Summary of Nasdaq rules for entering/canceling/modifying market-on-close (MOC)

• All MOC orders must be received at Nasdaq by 15:50:00 EST and cannot be cancelled after 15:50 EST.