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Key Takeaways
- The opening auction matches eligible orders at one price.
- Market-on-open orders request the auction price; limit-on-open orders set a price boundary.
- Paired quantity measures the shares that match at a candidate price.
- Imbalance measures the eligible quantity left on one side at that price.
- The completed auction sets the opening price and your fill; check the filled shares at once, because any remainder cancels or enters continuous trading by its instructions.
What is an opening auction?
An opening auction is the process that gathers eligible buy and sell orders before the session starts and matches them together at one price. That execution establishes the exchange’s official opening trade for the security. The process is also called an opening cross or opening call auction.
How the opening price is set: paired quantity and imbalance
At a candidate price, the paired quantity is the smaller of eligible buying and selling interest. The difference is the imbalance.
The worked $51 candidate has 180,000 eligible buy shares and 145,000 eligible sell shares. It pairs 145,000 shares for $7,395,000, with 35,000 shares left on the buy side.
The exchange evaluates candidate prices, applies its matching priorities and tie breakers, and enforces the applicable price controls. Published indications describe the order pool at that stage; the completed auction records the final price and quantity.
Formula
Opening matched quantity at a candidate price = min(eligible buy quantity, eligible sell quantity)- The auction algorithm evaluates candidate prices and applies venue-specific tie breakers and collars.
- Net imbalance equals eligible buy quantity minus eligible sell quantity at the reference or indicative price.
Worked Example
At a candidate opening price of $51.00, eligible buy interest totals 180,000 shares and eligible sell interest totals 145,000 shares.
- Paired quantity: min(180,000, 145,000) = 145,000 shares
- Buy imbalance: 180,000 − 145,000 = 35,000 shares
- Matched notional: 145,000 × $51.00 = $7,395,000
At the $51 candidate price, 145,000 shares pair for $7,395,000 and 35,000 shares remain on the buy side. The exchange evaluates eligible candidate prices, then applies its matching priorities, tie breakers and price controls to select the opening price.
Market-on-open and limit-on-open orders
A market-on-open order requests the auction price. A limit-on-open order adds a maximum buy price or minimum sell price. Venue-specific order types also include imbalance-only interest and eligible continuous-book orders.
After execution, reconcile the filled shares and remaining quantity. Order instructions determine whether a remainder cancels or continues into the book.
Opening imbalance times on Nasdaq and NYSE
Nasdaq begins opening-cross imbalance dissemination at 9:25 a.m. ET and schedules the cross for 9:30 a.m. NYSE begins opening imbalance publication for its listed securities at 8:00 a.m.; its DMM opens each security through the exchange’s auction process.
How traders read the opening auction
Compare the official open with the prior close, premarket trading and subsequent executions. The auction print records matched buyers and sellers. The following time and sales records show the prices and sizes that trade as the continuous market develops.
In the first minutes after the open, options flow shows which strikes and expirations traders are hitting, and the options profit calculator shows the position’s payoff at your premium and quantity from the opening price.
Limitations of the opening auction
- Read indications as a snapshot of the order pool at one stage, then take the final price and quantity from the completed auction.
- Choose the order by the price risk you accept. A market-on-open order has no price limit and accepts the auction price; a limit-on-open order fills only if the auction price meets its limit.
- Check the fill report for unmatched shares. Imbalanced interest leaves them, as the 35,000-share buy imbalance at $51 shows, and order instructions decide whether that remainder cancels or enters continuous trading.
- The listing exchange’s tie breakers, collars, order types and times decide how an opening order is handled, so check them for the venue before you send it; Nasdaq and the NYSE run different processes.
Bottom line
The opening auction concentrates pre-open interest into one official opening price and trade. Read paired quantity and imbalance in the published indications, choose market-on-open or limit-on-open by how much price risk you accept, and reconcile the fill against the official open and the trades that follow.
Clear answers
Frequently Asked Questions
Sources and Further Reading
How entries are sourced, calculated and updated: editorial methodology.