Order Execution

What Is Order Execution?

Order execution is the stage where an instruction to buy or sell a security is actually carried out. When an investor places an order through a brokerage, the order is sent to a trading venue such as an exchange or another market center, where it is matched against an opposing order. Once matched, the order is said to be filled, and the shares are bought or sold at the resulting price. An order that has been placed but not yet matched is still pending and has not been executed.

How Execution Works

Execution depends on the type of order. A market order tells the broker to trade immediately at the best available price, so it prioritizes speed over price certainty. A limit order sets a maximum buy price or minimum sell price, so it executes only if the market reaches that level. This gives price control but no guarantee of a fill. An order may also be filled in pieces, called partial fills, when there is not enough opposing interest at one price.

The broker decides where to route an order, often to several venues that compete for order flow. In the United States, regulators require brokers to seek best execution for client orders, meaning reasonable efforts to obtain the most favorable terms available under the circumstances. This standard does not guarantee the best possible price.

Why It Matters to Investors

The price shown on screen is not always the price received. Slippage is the difference between the expected price of a trade and the price at which it is actually executed. It can occur during fast markets or in thinly traded securities. Timing also matters. A market order placed during volatile periods may fill at a noticeably different price than the last quoted one.

Understanding execution helps investors match order types to their goals, such as whether speed or price control matters more. Execution quality can vary between brokers and venues, which is one reason brokers in the United States are required to publish reports on their order routing practices.