Best Execution

Best execution is the obligation of a broker, dealer or investment manager to obtain the most favourable result reasonably available for a client when executing an order to buy or sell a financial instrument. It is a duty about process and outcome taken together: the firm must have arrangements designed to deliver good results consistently, and must be able to show that it followed them.

The duty exists because clients cannot easily judge execution quality themselves and because firms face conflicts of interest in choosing where and how to trade. It is imposed by securities regulation in most developed markets, principally MiFID II in the European Union, equivalent rules of the Financial Conduct Authority (FCA) in the United Kingdom, and the rules of the Financial Industry Regulatory Authority and the Securities and Exchange Commission (SEC) in the United States.

Best execution is not simply the best price. Regulation lists several factors that a firm must weigh according to the client, the order and the instrument:

• Price. The level at which the order is filled, relative to the market at the time.
• Costs. Commissions, venue fees, clearing and settlement charges and taxes.
• Speed. How quickly the order is executed, which matters most in fast-moving markets.
• Likelihood of execution and settlement. The chance that the order is completed in full and settles without problems.
• Size and nature of the order. Large or illiquid orders may need to be worked over time to limit market impact.

For retail clients under MiFID II, the best possible result is determined by total consideration: the price of the instrument plus all costs of execution. For professional clients, other factors such as speed or certainty can take precedence.

MiFID II requires investment firms to take all sufficient steps to obtain the best possible result for their clients, a stricter wording than the "all reasonable steps" of the first directive. Firms must establish a best execution policy that names, for each class of instrument, the venues and brokers they use and the reasons for choosing them. Clients must be given appropriate information about the policy and consent to it. Firms must monitor the effectiveness of their arrangements, review them at least annually, and be able to demonstrate to a client on request that an order was executed in line with the policy.

Where a client gives a specific instruction, for example to trade on a named venue, the firm satisfies its duty by following it for the aspects covered. The original rules also required periodic public reports by venues on execution quality and by firms on their top five venues. These reports were widely judged to be little used, and the European Union and the United Kingdom have since removed them.

The duty applies to all instruments, including bonds and over-the-counter derivatives, where there may be no single visible market price. In these markets firms show best execution by gathering quotes from several dealers, for instance through a request for quote (RFQ), or by checking the fairness of a price against market data and models.

In the United States, the industry rule requires a broker-dealer to use reasonable diligence to find the best market for a security and to buy or sell there so that the price to the customer is as favourable as possible under prevailing conditions. Brokers must conduct regular and rigorous reviews of execution quality. Separately, market structure rules protect displayed quotations across exchanges, so that orders are generally not executed at prices worse than the best displayed bid or offer nationwide. Investment advisers owe best execution to their clients as part of their fiduciary duty.

A long-running controversy concerns payment for order flow (PFOF), in which a retail broker receives payments from a wholesale market maker for sending it orders. Supporters say customers receive prices better than the public quote; critics say the payment creates a conflict with the broker's duty. The practice is permitted with disclosure in the United States, while the European Union has legislated to prohibit it.

Firms evidence best execution through transaction cost analysis, which compares each fill with benchmarks. Common benchmarks include the price when the order arrived, the volume-weighted average price (VWAP) over the trading period, and the quoted bid-ask spread. The total cost relative to the price when the investment decision was made is the implementation shortfall, and the gap between expected and achieved price is slippage.

Results feed back into order routing decisions. Because trading in a single share is spread over many exchanges, a multilateral trading facility (MTF), a systematic internaliser and other non-displayed venues, liquidity fragmentation makes automated routing and continual comparison necessary.

Best execution is hard to define precisely, since the best outcome can only be judged against alternatives that were not taken. Compliance has at times become an exercise in documentation that offers little insight to clients. The absence of a consolidated record of prices in Europe long made comparisons harder; a consolidated tape for European Union shares and exchange-traded funds, whose provider was authorised in July 2026, is meant to address this. Enforcement cases have generally concerned firms that failed to monitor execution quality, routed orders to affiliates without justification, or did not manage conflicts created by venue rebates and inducements.

• European Securities and Markets Authority
• Financial Industry Regulatory Authority