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Stocks, ETFs, and Equities Macro · T+1 Settlement and Equity Mechanics

Market-on-open and market-on-close orders

Explain how MOO and MOC orders work and when to use them.

3 min read+25 XPLesson 16 of 55
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Stocks, ETFs, and Equities Macro

T+1 Settlement and Equity Mechanics

Lesson 16 of 5529%
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Lesson 16 of 55Stocks, ETFs, and Equities MacroT+1 Settlement and Equity Mechanics

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Explain how MOO and MOC orders work and when to use them.

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Two auctions every day

US equity markets do not just open and close — they auction. At 9:30 AM Eastern, every NYSE and NASDAQ stock runs an opening auction to set the day's first official price. At 4:00 PM, another auction sets the closing price. These two auctions are usually the highest-volume trades of the day, and they have special order types built around them.

Wick points at a chalkboard listing MOO by 9:28 AM and MOC by 3:50 PM Eastern, teaching the deadlines for the opening and closing auctions.Auction order timesMOO: by 9:28 AM ETMOC: by 3:50 PM ETFill at 9:30 or 4:00
Wick saysSend MOO orders before 9:28 AM and MOC orders before 3:50 PM to join the auctions.

Market-on-Open (MOO) is the order type that guarantees you participate in the opening auction. You submit it before 9:28 AM Eastern. At 9:30, the exchange aggregates all the MOO orders, all the limit orders priced into the auction, and prints a single opening price that clears the largest possible volume. Your MOO fills at that single price, no matter what.

Market-on-Close (MOC) works the same way for the close. Submit before 3:50 PM Eastern. At 4:00 PM, the exchange runs the closing auction and your MOC fills at the official closing print. The closing auction is the largest single liquidity event of the day on most US stocks — index rebalances, ETF rebalances, mutual fund flows, and risk-off institutional positioning all funnel into this print.

Wick checks a clipboard: official close price, tight spreads and steady slippage are ticked, and caps your fill price has a red X, teaching what MOC does and does not do.Why use MOCOfficial close priceTight spreadsSteady slippageCaps your fill price
Wick saysMOC gets you the official close with deep liquidity, but it does not cap your price.

When should you use MOC over a regular market order at 3:59? Three reasons. One, you get the official closing price for benchmarking. Two, you get the tightest spreads of the day, because so much volume converges into one print. Three, your slippage is more predictable than firing a market order into thin late-day liquidity. Same for MOO at the open. If you do not need an exact entry price, the auction is your friend.

Wick shows a green card about using LOO or LOC for a price cap and a coral card about expecting MOO to avoid a gap, teaching the risk of uncapped auction orders.Do thisUse LOO or LOCwhen you need acapNot thisExpect MOO tododge a gap-up fill
Wick saysIf overnight news lifts the open 8%, a MOO buy fills there. Add a limit if price matters.

Recap: MOO fills at the 9:30 opening auction (submit before 9:28). MOC fills at the 4:00 closing auction (submit before 3:50). Best liquidity of the day, but no price ceiling. Use LOC and LOO variants if you want a limit.

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1. You want to sell 50 shares at exactly the official closing price. Which order type do you use?

2. Big risk of using a Market-on-Open buy order?

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