Rule 605 (Execution Quality)
SEC Rule 605 requires market centers — including national securities exchanges, registered market makers, and electronic communication networks — to publish monthly standardized reports on the quality of order executions they provide, disclosing statistics on price improvement, fill rates, and execution speed that allow investors and broker-dealers to compare execution quality across venues.
Execution quality has multiple dimensions: price improvement over the national best bid or offer (NBBO), the speed with which orders are executed, fill rates (the percentage of eligible orders that receive full execution), and effective spreads. Before Rule 605, these metrics were not standardized or publicly available, making systematic comparisons across execution venues essentially impossible.
Rule 605, adopted in 2000 alongside Rule 606, addresses this gap by requiring market centers to publish monthly execution quality statistics in a standardized format. The required data includes, for each order type (market orders, marketable limit orders, inside-the-quote limit orders, and at-the-quote limit orders) and for multiple order size tiers: the number of orders received, the percentage filled at the quote, the percentage filled with price improvement, the average price improvement per share for improved orders, the average execution speed, and realized spread statistics.
Realized spread — the difference between the execution price and the midpoint of the bid-ask spread immediately after execution — is a particularly important metric because it measures the actual revenue captured by the market maker at the expense of the investor, net of any immediate price movement. A small realized spread indicates that the market maker provided genuine liquidity at a competitive price; a large realized spread may suggest that the market maker benefited from informational advantages or order flow selection.
For institutional investors conducting best execution analysis, Rule 605 data is a foundational input. Transaction cost analysis (TCA) systems operated by investment managers routinely incorporate Rule 605 statistics to benchmark the execution quality received from their broker-dealers against what a given venue publicly reports, enabling identification of execution venues that systematically underperform their disclosed averages.
Broker-dealers use Rule 605 data as part of their routing decision frameworks. Automated smart order routing systems can incorporate venue-level execution quality metrics alongside fee structures to make real-time routing decisions that weigh both the cost of accessing a venue and the expected quality of execution.
Critics have raised several limitations of Rule 605 data. The statistics are published monthly with a lag, making them unsuitable for real-time routing optimization. The statistics are aggregated across all orders, which may obscure important differences in execution quality for specific stock types, market conditions, or order characteristics. The SEC has solicited input on modernizing Rules 605 and 606 to incorporate additional metrics and more granular breakdowns, particularly for retail-size orders.