Best Execution

Best execution is a foundational principle of U.S. securities regulation. It holds that a broker-dealer acting as an agent for its customer has a duty to obtain the best possible result for that customer when executing trades — not merely an adequate result or one that is convenient for the broker. The obligation arises from common law agency duties and is codified in FINRA Rule 5310, which applies to FINRA member broker-dealers handling customer orders in equity securities.

Best execution is not limited to price alone, though price is typically the most significant factor. FINRA Rule 5310 requires firms to consider a range of relevant factors, including: the character of the market for the security (e.g., volatility, liquidity), the size of the transaction, the terms of the order (e.g., limit versus market), the accessibility of the quotation, and the terms and conditions of competing quotations. A broker cannot satisfy best execution simply by routing to the venue offering the best price if that venue has such low liquidity that the order is unlikely to be filled promptly.

Broker-dealers are expected to conduct regular and rigorous review of their order routing practices to ensure their execution quality meets best execution standards. These reviews must be documented, and firms must have policies and procedures reasonably designed to achieve best execution across varying market conditions. FINRA examiners review best execution practices as part of routine broker-dealer examinations.

Best execution interacts directly with payment for order flow (PFOF). The SEC and FINRA have repeatedly examined whether brokers that accept PFOF can genuinely satisfy their best execution obligations, given that PFOF creates an incentive to route to paying market makers regardless of execution quality. SEC Rule 606 disclosures and Rule 605 execution quality statistics — which market makers must publish — give investors and regulators tools to assess whether PFOF-intensive routing arrangements produce competitive execution outcomes.

For retail investors, best execution is most practically evaluated by comparing the execution prices received against the prevailing NBBO at the time of order receipt. Price improvement — receiving an execution price better than the best published bid or offer — is one measurable metric of execution quality. Investors can review execution quality reports on their broker's website or request trade confirmations that disclose execution venue and timing.