Opening and Closing Auctions: How MOC, LOC and MOO Orders Execute

Understand how opening and closing auctions execute MOC, LOC and MOO orders, interpret indicative prices and imbalances, and manage slippage, deadlines and execution costs.

A market-on-close order chooses an auction, not a known price

A market-on-close order, or MOC, requests execution in the closing auction without specifying a price limit. It is not an instruction to execute at the last price visible when the order is submitted. Nasdaq explicitly states that MOC execution is not guaranteed in its opening and closing auction FAQ.

That distinction matters for anyone managing a closing-price benchmark. An auction fill can align with that benchmark while still being substantially worse than the price available when the trading decision was made.

The practical question is therefore not simply whether an order “gets the close.” It is which auction the instruction reaches, what price protection it carries, when it becomes difficult to change, and what happens to any unexecuted balance.

This article focuses on US equity auctions. Its deadlines and order-handling examples should not be treated as rules for other jurisdictions.

How auction execution differs from continuous trading

During an auction, eligible orders are brought together for execution at a common clearing price rather than necessarily trading as they arrive. Nasdaq combines auction interest with eligible continuous-book interest in its opening and closing crosses, as explained in its auction overview.

Price selection follows exchange-specific rules. Nasdaq’s process seeks to maximise executable volume, then applies tie-breakers that include minimising unmatched interest. It is not simply an average of submitted prices. The detailed methodology appears in the Nasdaq equity trading rules.

For an execution team, the implication is important: a large auction is not automatically an inexpensive auction. Concentrating interest can provide access to substantial opposing liquidity, but the eventual price still depends on the eligible demand and supply.

Nor is the displayed continuous-market quote a promise of the auction result. Treat the quote and the auction indication as different observations, not interchangeable execution prices.

Opening auctions are not interchangeable across venues

On the NYSE, a designated market maker, or DMM, opens each security. The opening process begins at 9:30 a.m. Eastern Time, but an individual security may open later.

Operationally, that means an opening-order workflow should track the security’s actual auction status rather than relying solely on a wall clock.

MOC, LOC, MOO and LOO orders

Nasdaq distinguishes market and limit instructions for both opening and closing crosses in its order-type documentation.

Order	Intended execution	Price protection	Main trade-off
Market-on-close, MOC	Closing auction price	No submitted limit	Exposure to an unexpectedly adverse closing price
Limit-on-close, LOC	Closing auction, subject to its limit	Maximum purchase price or minimum sale price	Partial execution or no execution
Market-on-open, MOO	Opening auction price	No submitted limit	Exposure to overnight repricing
Limit-on-open, LOO	Opening auction, subject to its limit	Maximum purchase price or minimum sale price	Missing the opening execution if the limit is incompatible

A limit is a boundary, not a requested execution price. A buy LOC can execute at an auction price below its limit; a sell LOC can execute above its limit. Nasdaq’s auction FAQ explains how market and limit instructions participate at the cross price.

Consider a qualitative example. An operations team needs to reduce an equity position at the close but has a minimum acceptable sale price. A sell LOC expresses that boundary. If the auction clears below it, the intended reduction may not happen.

A sell MOC removes that price boundary, but replaces non-execution risk with unrestricted price exposure within the applicable auction safeguards. Neither instruction eliminates execution risk; each places it somewhere different.

The same distinction applies at the open. MOO emphasises participation at the opening price, while LOO adds a price constraint. The appropriate operational test is whether an unfilled order or an adverse fill would cause the greater problem.

Reading indicative prices and imbalance data

Auction data describes a conditional state of the order book. It does not reserve an execution price.

Useful fields include paired quantity, unmatched quantity, imbalance direction and the reference price used for the calculation. The NYSE defines these fields in its auction information guide.

Read those fields together:

Paired quantity describes interest that can currently match under the calculation.
Imbalance direction identifies the side with unmatched interest.
Imbalance quantity describes the unmatched amount at the relevant reference price.
The reference price identifies where that calculation is being made.

These definitions come from the NYSE auction guide; field names and calculations should still be checked against the actual venue feed.

A buy imbalance should therefore be read as a conditional liquidity observation, not a standalone instruction to purchase. It does not establish what the next indication, final auction price or subsequent market price will be.

Near and far clearing prices

Nasdaq distinguishes a near indicative clearing price, incorporating eligible continuous-book interest, from a far indicative clearing price based on auction-book interest. Its auction FAQ explains the distinction.

As an analytical interpretation, a large separation between those indications deserves investigation: the result may depend materially on the different pools of eligible liquidity. That is a sensitivity check, not a directional forecast.

A practical monitoring screen should also show message timestamps and feed status. A precise-looking indication is not useful if the operator cannot establish how fresh it is.

Do not confuse a reference price with an executable promise

An imbalance calculated at a reference price answers a conditional question. It does not say that every eligible order will execute there.

A useful desk question is: “What has changed since this snapshot?” Review the indication alongside newly acknowledged orders, cancellation restrictions and the latest auction status. Avoid turning a data label such as “buy imbalance” into a trading thesis without examining its context.

Deadlines: entry and cancellation are separate controls

An exchange can still accept new orders after ordinary cancellation rights have narrowed. Treating the entry cutoff as the cancellation cutoff is therefore a dangerous shortcut.

For the NYSE closing auction, the standard MOC/LOC entry cutoff is 3:50 p.m. Eastern Time. The exchange describes exceptions for orders offsetting a significant imbalance and states that cancellation requests are rejected after that point.

Nasdaq’s standard MOC entry window ends immediately before 3:55 p.m. Eastern Time, while ordinary cancellation and modification end immediately before 3:50 p.m.. Limited legitimate-error procedures apply thereafter; they are not a general right to change a trading decision.

Late LOC handling is different again. Nasdaq permits qualifying submissions immediately before 3:58 p.m. Eastern Time, subject to reference-price conditions and rejection or repricing instructions.

These are exchange rules, not a promise about a particular broker’s customer interface. For each route, obtain written confirmation of:

The customer submission deadline.
The cancellation and replacement deadline.
Whether late instructions are rejected or transformed.
Whether the route actually reaches the intended auction.

Also validate shortened-session calendars rather than reusing normal-session settings. Nasdaq’s closing-cross rules explicitly provide adjusted imbalance-publication timing for early closes.

Measuring slippage without hiding the benchmark

The closing price is useful when the execution objective is to match the close. It is insufficient when the question is whether delaying execution was costly. Nasdaq confirms that its cross establishes the official closing price for Nasdaq-listed securities in its Closing Cross overview.

For internal analysis, separate these comparisons:

Decision-price slippage: the fill versus the price when the trade was authorised.
Auction-benchmark slippage: the fill versus the relevant official auction price.
Indication movement: the final auction price versus a saved, timestamped indication.
Completion: the executed quantity versus the intended quantity.

These are proposed reporting lenses, not interchangeable definitions of execution quality.

For example, a portfolio team may receive its intended closing-auction fill after the market has moved adversely since authorisation. Its auction-benchmark comparison can look satisfactory while its decision-price comparison looks poor.

Conversely, a price-constrained order may avoid an unacceptable fill but leave exposure that still requires management. A report showing only executed trades would miss that outcome.

For each auction, retain the instruction, authorised quantity, limit, route, acknowledgements, saved indications, executions and final residual. Record exceptions separately from routine fills.

Risks and costs

Price risk and market impact

MOC and MOO lack a submitted limit. Treat participation at an unknown price as a risk decision, not an administrative convenience. Nasdaq’s auction FAQ also cautions against assuming guaranteed MOC execution.

For internal stress testing, examine an adverse indication move and a weaker-than-expected supply of opposing liquidity. Ask whether the resulting exposure would remain within the mandate.

Non-execution and residual exposure

LOC and LOO provide price constraints, not certainty of completion. Budget for the operational cost of an unfilled balance as well as the visible transaction charge.

Do not assume all residuals disappear immediately after the auction. Under Nasdaq’s current rules, qualifying LOC balances submitted through specified protocols can participate in its Extended Trading Close unless that participation is disabled. Verify the applicable settings against the Nasdaq order-handling rules.

Fees and data costs

Auction execution is not inherently free. Nasdaq publishes distinct auction charges and eligibility conditions in its trading price list, while imbalance information is available through subscription channels described on its auction information page.

For budgeting, request an all-in broker schedule covering commissions, auction pass-throughs and data access. Do not assume an exchange member’s published rate is the customer’s final charge.

Safeguards and operational failures

Auction price protections do not establish the price a trader considers acceptable. Nasdaq publishes validation and benchmark parameters in its system settings.

A sensible control checklist should also cover stale data, duplicate submissions, incorrect sides, missed acknowledgements and unresolved cancellation requests. Never treat a cancellation request as proof that exposure has been removed; require a confirmed final order state.

Bottom line

A market-on-close order seeks auction execution without a price limit. LOC and LOO add price boundaries but introduce completion risk.

The central discipline is to separate price, participation and operational certainty. Read indications as conditional snapshots, verify the venue and broker deadlines, and measure both execution cost and any exposure left behind.

This article provides information and education, not personalised investment advice.