Execution

Stock trading dictionary: meaning, example and how traders use it.

Last updated: October 17, 2026

Definition: Execution is the process of completing a buy or sell order, the moment an order is filled at a specific price and quantity. Execution quality covers the price received, the speed of the fill and the likelihood the order is filled at all.

How trade execution works

When you submit an order, your broker routes it to a venue such as an exchange, a market maker or an alternative trading system. There it is matched with an opposite order and executed. The broker then reports the fill to you, and the trade settles on T+1 for US stocks, when cash and shares actually change hands. A large order may be executed in several pieces at different prices, called partial fills.

Execution speed is measured in fractions of a second for most liquid stocks. Your confirmation shows the exact time, price and number of shares filled, which you can compare with the quote you saw.

Order types and execution

  • Market order: executes immediately at the best available price; certain to fill in liquid stocks, but the price is not guaranteed.
  • Limit order: executes only at your limit price or better; price is controlled, but the order may not fill.
  • Stop order: becomes a market order when a trigger price is reached.
  • Stop-limit order: becomes a limit order at the trigger, which may leave it unfilled in a fast move.

Slippage example

Suppose a stock quote shows a bid of $50.00 and an ask of $50.05, with only 200 shares offered at the ask. You send a market order to buy 1,000 shares. You might buy 200 at $50.05, 300 at $50.07 and 500 at $50.10, an average of about $50.08. The difference between the $50.05 you saw and the $50.08 you paid is slippage, costing about $30 on the trade. A limit order at $50.05 would have avoided the higher prices but might have filled only 200 shares.

Best execution

US brokers have a regulatory duty of best execution: they must use reasonable diligence to seek the most favorable terms reasonably available for customer orders. That considers price, speed, likelihood of execution and the size of the order. Brokers publish reports on where they route orders and on execution quality. Some receive payment for order flow from market makers, a practice that is disclosed and debated, so execution quality can vary between brokers even when commissions are zero.

Improving execution

Trading during the regular session, when liquidity is deepest, usually means tighter spreads. Using limit orders in thinly traded stocks, in pre-market trading and after hours helps control price. Splitting large orders and avoiding the first minutes after the open, when volatility is often highest, can also reduce slippage. Active traders monitor their average fill against the quoted price to measure execution quality over time.

Frequently asked questions

What does it mean when an order is executed?

It means the order has been filled: your shares were bought or sold at a specific price. Settlement of the trade follows on T+1 for US stocks.

Why did my order fill at a different price than I saw?

Prices can change between the moment you view a quote and when the order reaches the market, and large market orders may fill at several price levels. This is called slippage.

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For information only, not investment advice. See the disclaimer.