Timing is everything when it comes to trading, and the stock markets behave very differently throughout the trading day. Price discovery refers to the fact that prices are formed differently during each phase, from the opening auction call through to continuous trading.
Understanding the complexities of price mechanics helps traders navigate market volatility, optimize spreads, and improve execution.
What is an Open Auction (Opening Auction) in Trading?
Every trading day begins with an opening auction at 9.30 am EST. It is the culmination of an intricate price discovery process whereby exchanges begin accepting orders from 4 am EST. This huge order flow is collected before the market opens and then processed simultaneously in milliseconds at the opening auction.
Whether traders place orders via the LSE opening auction, the Nasdaq opening auction, or the NYSE opening auction, this environment creates a high level of liquidity and a level playing field for all orders, regardless of size.
Three different types of orders are collected:
- Market-on-Open Order that will execute at the price the auction determines;
- Limit-on-Open orders that have a specified price limit and will only be filled if the opening auction clears at an accepted price;
- and standard market orders.
The concept of auction in trading sees orders matched at a single definitive price point (the discovery price) as part of a process that helps to establish the first tradable price of the day. This price is typically based on the maximum number of shares traded and the minimum imbalance.
What is Continuous Trading and How Does It Work?
As another key phase in the trading day, the continuous trading session sees orders matched in real time throughout the day. Within this market mechanism, market makers facilitate the trades on secondary market exchanges, matching buyers and sellers on the open market.
They place buy or sell orders, and these are matched instantly and continuously as soon as possible, and when a compatible order exists.
Unlike the single price auction, the continuous trading market involves buyers and sellers interacting continuously, and prices move based on supply and demand.
Market makers play a major role in the continuous trading process to ensure a streamlined system with buy and sell quotes consistently available.
Price Discovery in Opening Auction vs Continuous Trading
Price discovery is a process by which the market ascertains how much an asset is worth and its fair market value based on the price at which buyers and sellers are willing to pay and accept.
During the open auction process, prices are determined by a single equilibrium price that considers how many orders have accumulated before the open market call and how much these are worth.
This process finds the closest point at which supply equals demand, but it offers just a small snapshot of the market as it only reflects activity in that precise moment.
For continuous trading, price discovery is constantly evolving throughout the trading day as traders place buy and sell orders. As orders are ongoing, this means prices adjust frequently as part of a highly responsive – and often volatile – process.
The market often sees price gaps at the open due to market activity overnight when orders build up as extended-hours traders respond to market news. If demand and supply are imbalanced at market open, this will result in a major price gap compared to the close of the market the previous day.
As the session continues, prices typically even out and move more smoothly because orders are being matched in real-time. This means prices can move more gradually and more easily as they adjust trade by trade with buyers and sellers at.
This allows the market space to adjust more evenly to changes and avoid the large spikes seen at open auction due to suppressed order flow overnight.
Why Volatility and Execution Differ Between Open Auction and Continuous Trading
Volatility is often higher at the open due to a combination of accumulated overnight news, order imbalance, and lower immediate liquidity.
Regarding overnight events, market-moving events such as earnings reports or geopolitical instability that happen during market close can trigger major trading activity.
However, all these trades will be executed simultaneously at the opening auction call, which could lead to price spikes following the open as the market adjusts to trading responses. This triggers a major imbalance between buy and sell orders, meaning the market must adjust to compensate for this gap.
As execution is completed at one single price, this can mean less control and less stability. Liquidity is also far more concentrated in the phase immediately following the open auction call, meaning small shifts in the supply-demand dynamics can have a larger-than-typical impact on asset prices.
When it comes to continuous trading, buyers and sellers can place trades at multiple price points, offering much more flexibility and a typically more stable trading environment.
Liquidity is also higher due to greater depth at multiple price levels. Traders have space to react to news in real-time and at different paces, resulting in smoother price movements.
However, trades during this phase may be vulnerable to slippage, while larger orders can have a significant impact on market movements and pricing.
Opening Auction vs Continuous Trading FAQs for Traders
What are the Benefits of Price Discovery for Traders?
Price discovery is an essential trading tool because it helps traders identify supply and demand on specific assets. It helps to determine key entry and exit points, inform risk management strategy, and support traders in understanding whether to open a long or short position.
What is an Opening Auction in the Stock Market?
The opening auction takes place at the start of the trading day and sees the execution of all buy and sell orders accumulated overnight at a single price. This price aims to be the point at which supply and demand are equal, or as close to this point as possible, and is the price at which the asset opens on the market.
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