What Is SEC Rule 605?

SEC Rule 605, formally known as Rule 605 of Regulation NMS, is a transparency regulation issued by the U.S. Securities and Exchange Commission (SEC). It requires market centers — such as stock exchanges, alternative trading systems (ATSs), and market makers — to publish standardized monthly reports on the quality of trade executions for certain equity securities. These reports are intended to help investors and regulators evaluate how well market centers are fulfilling their duty of best execution, particularly in terms of speed and price improvement.

The rule originally emerged as part of the SEC’s broader initiative to promote competition, market transparency, and investor protection in U.S. equity markets. It was adopted in 2000 as Rule 11Ac1-5 under the Securities Exchange Act of 1934 and was later reclassified as Rule 605 during the modernization of Regulation NMS (National Market System).

Purpose and Objectives

The primary purpose of Rule 605 is to improve the ability of investors and regulators to assess the execution quality of different market centers. Prior to its adoption, investors had limited insight into how quickly and at what prices their orders were being executed, which made it difficult to assess execution quality or to compare competing trading venues.

Rule 605 aims to:

• Foster transparency by requiring public disclosure of trade execution statistics.
• Encourage competition among market centers based on execution quality.
• Support investor decision-making through standardized metrics.
• Enable brokers to evaluate their routing decisions and fulfill their best execution obligations more effectively.

By establishing a uniform set of data and reporting requirements, Rule 605 attempts to level the playing field and promote accountability in order handling and execution practices.

Key Reporting Requirements

Under Rule 605, market centers must report detailed data for orders in National Market System (NMS) stocks that are market orders or marketable limit orders and fall within a defined size threshold (generally 10,000 shares or less). The reports are required monthly and must be made publicly available on the market center’s website.

Each Rule 605 report must include the following execution quality metrics, broken down by order size and stock price:

• Effective spread: A measure of execution cost calculated by comparing the trade execution price to the midpoint of the national best bid and offer (NBBO) at the time the order was received.
• Rate of price improvement: The percentage of orders executed at a price better than the NBBO.
• Rate of price disimprovement: The percentage of orders executed at a price worse than the NBBO.
• Execution speed: The average time between order receipt and execution.
• Fill rate: The proportion of orders that were executed in whole or in part.

These metrics are aggregated and categorized into order size groups and stock price intervals to facilitate comparison across different market centers.

Scope and Applicability

Rule 605 applies to all U.S.-registered equities exchanges, ATSs, and over-the-counter market makers that execute covered orders in NMS stocks. Covered orders are defined narrowly under the rule: they must be market orders or marketable limit orders of 10,000 shares or fewer and must not be directed by the customer to a specific venue.

Broker-dealers that route orders to market centers but do not execute trades themselves are not directly subject to Rule 605 reporting obligations, though they must consider the data in meeting their duty of best execution under FINRA Rule 5310 and other regulatory standards.

Rule Evolution and Regulatory Considerations

Since its adoption, Rule 605 has faced criticism and calls for modernization. Critics argue that the rule does not capture the complexity of modern trading practices, including the rise of algorithmic trading, the prevalence of non-displayed orders, and differences in order types. The SEC has acknowledged these concerns and has explored potential updates to better reflect today's market structure.

In 2020 and again in 2022, the SEC issued proposals to amend Rule 605 to expand the range of order types covered, introduce more granular reporting categories, and enhance disclosure of execution quality on odd-lot and retail orders. These proposals reflect ongoing regulatory interest in adapting the rule to current trading dynamics and providing more meaningful information to investors.

Relevance to Investors and Market Participants

For institutional investors, regulators, and financial professionals, Rule 605 data offers a valuable tool to benchmark execution quality and hold trading venues accountable. While retail investors rarely consult Rule 605 reports directly, the availability of these reports encourages competitive behavior among market centers, leading to better execution outcomes across the board.

Broker-dealers may also use Rule 605 data to audit their routing strategies and support disclosures under Rule 606, which focuses on order routing practices. Together, these rules form a key part of the SEC’s efforts to ensure best execution and market fairness.

The Bottom Line

SEC Rule 605 serves as a foundational transparency rule in the U.S. equity markets by mandating public disclosure of execution quality statistics from market centers. Although technical in nature and limited in scope, the rule plays an important role in supporting fair competition, enabling investor oversight, and informing regulatory policymaking. As markets evolve, further enhancements to Rule 605 may be necessary to maintain its effectiveness in promoting best execution and transparency in modern equity trading.