What it means
Many exchanges end their trading day with an auction. Buy and sell interest is collected and matched at one clearing price, which becomes the official closing price.
A market-on-close, or MOC, order joins that auction and takes the resulting price. Unlike a limit order, it does not let the investor set a maximum purchase price or minimum sale price.
The New York Stock Exchange describes its closing auction as a way to concentrate liquidity and establish a closing price. It publishes imbalance information before the auction so participants can see whether buying or selling interest dominates.
Its order rules also set submission and cancellation cutoffs. Other exchanges have different mechanics, and those details matter if a transaction has to happen on a particular day.
Why care about the close? Index funds often measure performance and rebalance holdings using closing prices.
If a fund owns the benchmark in the same proportions at the close, it avoids a mismatch between its trade price and the benchmark's published level. A company buying back shares may also want an orderly auction rather than chasing prices through thin intraday trading.
The advantage comes with risk. Because the final price is not known when an MOC order is entered, a sudden news release or a large imbalance can create a much worse outcome than expected.
Investors who cannot accept any price should use a limit-on-close order if the venue allows it, accepting that it might not execute. Orders can also fail to enter if sent after the exchange cutoff, and some exchanges restrict cancellations during the final minutes.
An instruction sent to a broker is not proof of participation until the broker confirms acceptance. The responsible habit is to check both the venue's rules and the resulting fill.
In practice
Real-world examples.
Example
An index fund must add a new constituent at the close of a quarterly rebalance. It places an MOC buy order so its transaction price matches the benchmark calculation as closely as possible.
Example
A treasury team sells a small block of listed shares through a closing auction, expecting deep liquidity. Unexpected earnings news arrives just before the close, and the final price is lower than the mid-afternoon quote. The market order had no price floor.
Example
A broker receives an MOC order after the venue's permitted submission window. The team instead schedules the trade for the next session and records the missed benchmark date rather than assuming the order executed.
Formula
Calculation
There is no fixed execution-price formula for the investor. The auction determines a single clearing price under the venue's rules; an MOC buy pays that price and an MOC sell receives it, before broker fees and taxes. Quantity must still be checked against the fill confirmation.
Worked example. An investor enters an MOC order to buy 10,000 shares. The last continuous quote before the cutoff is $50.00, so she expects to spend about $500,000.
- News arrives and the auction clears at $50.40. Cost = 10,000 x $50.40 = $504,000.
- Surprise cost = $504,000 - $500,000 = $4,000, which is $4,000 / $500,000 = 0.8%.
- A limit-on-close order with a $50.20 limit would not have filled at that clearing price, so she would have avoided the surprise but missed the benchmark purchase.Case study
Seen in the real world.
Fictional example: Meridian Pension Trust, a fictional retirement fund, was due to track a changed equity index after a Friday rebalance. Its manager identified three newly added shares and instructed the broker to buy at the closing auction. The broker explained the venue's deadline, estimated the likely imbalance, and warned that the final price could jump. Meridian accepted that price uncertainty because missing the benchmark change would create tracking error throughout the next week.
Two of the shares filled near the afternoon quote; the third rose sharply into the close. The operations team reconciled each final fill with the exchange's official closing price and broker confirmation. The investment committee then recorded both the benchmark benefit and the cost of the auction price surprise. The lesson was not that closing auctions are cheap, but that their purpose is precise timing at an uncertain price.
Watch out
Common mistakes.
- Treating an MOC order like a limit order, even though the final price is unknown when submitted.
- Missing an exchange cutoff or cancellation restriction and assuming the trade still reached the auction.
- Using the closing auction for a large trade without considering imbalance, market impact and the venue's liquidity.
Questions
People also ask.
Will an MOC order get the day's last traded price?
It seeks the official closing auction price, not necessarily the last continuous-trading print. Venue rules determine the final price and how the order participates.
Can I cancel it at any time?
No. Exchanges impose cutoffs and may restrict changes close to the auction. Check the current rule and broker confirmation before relying on cancellation.
When is it useful?
It fits an investor who needs to track an index valued at the official close. It is less suitable when a strict minimum sale or maximum purchase price matters more than execution.
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