Why did my limit order on close (CLS) not execute?

I placed a limit order for the stock AZ to execute at market close (CLS) at a price of $2.80. My order did not execute and instead was canceled at close, but the closing price of AZ was $2.89. Then, I placed an after hours limit order for $2.89, and the order partially executed.

I don’t understand. How did the closing price end up above my limit sell price, yet my order did not execute?

Fellow trader here, and this is an interesting question so I’ll take a shot. First of all I’m assuming this is to sell an existing long position, not to open a new short position, correct? (Because then you’d have to worry about short availability.)

Exactly what time did you place the order? AZ is listed on NASDAQ, where limit-on-close (LOC) orders to participate in the closing auction cannot be entered after 3:58 p.m. EST. So if you placed the order less than 2 minutes before close, you would not be filled.

Otherwise, AZ appears to be a thinly-traded stock, so there may not have been enough auction volume for you to participate.

Let’s say the entire auction order book before you consisted of a market-on-close (MOC) order to buy 100 shares, and a MOC order to sell 100 shares. Then you added your LOC sell order, and no other buy orders came along. You would not be filled in the closing auction, because who would you sell to? There’s no offsetting buy orders. The auction would solely consist of those 100 shares from those aforementioned 2 parties at 2.89, which would be the closing print.

LASTLY, be careful with on-open and on-close orders. Did you know that Alpaca charges commissions? Yeah I was using too many LOO/LOC orders so they started calling me a professional trader instead of retail, and charged me $0.004/share commissions. It happened to many other people as well, see: Commission-free? Alpaca is trying to charge me commissions!

Pretty sketchy bait-and-switch if you ask me since their entire website is plastered with “commission-free” language.

Anyway hope that helps. Auctions (aka opening/closing crosses) are kinda tricky but you can google the exchange and see details of them e.g. https://www.nasdaqtrader.com/content/productsservices/Trading/ClosingCrossfaq.pdf