Best Execution and Execution Quality

Best execution is a broker's obligation to seek the most favourable terms reasonably available for a customer's order. It is not just about price. It also covers speed, the likelihood of execution, the size of the order and the total cost. For traders, understanding best execution helps you judge whether "commission free" is really cheap and whether your broker is filling your orders well.

What best execution covers#

Regulators describe several factors a broker must weigh:

In the United States, FINRA Rule 5310 sets out the duty for broker-dealers. In Europe, MiFID II requires firms to take all sufficient steps to obtain the best possible result. Neither rule guarantees a specific price; they require a reasonable process and regular review.

Price improvement#

Price improvement means getting a better price than the displayed best quote.

Wholesale market makers often provide small price improvement on retail orders. Brokers publish statistics on how often and by how much their customers' orders are improved.

Routing and conflicts of interest#

Brokers may route orders to venues that pay them, through payment for order flow or exchange rebates. That creates potential conflicts with best execution, which is why rules require brokers to disclose routing practices and compare execution quality across venues regularly. In the US, SEC Rule 606 reports show where brokers route orders and what they receive, and amended Rule 605 reports cover execution quality statistics. See Order Routing and Smart Order Routing.

How to judge your own execution#

1. Record the quote when you send an order and compare it with your fill.
2. Track slippage on stops and market orders over many trades. See Slippage Analysis.
3. Check limit order fill rates: how often do your limits fill when the price touches them?
4. Compare total costs: commissions plus spreads plus slippage, not commissions alone. See All-In Trading Cost.
5. Read your broker's routing and execution quality reports.

Best execution for institutions#

Funds measure execution against benchmarks such as the arrival price, VWAP or the closing price, and report the results to clients. The broadest measure, Implementation Shortfall, compares the actual result with the price at the moment the decision to trade was made, capturing delay, market impact and missed trades.

What it does not mean#

• It does not mean every order fills at the best price ever seen that day.
• It does not cover your choice of order type. A market order in a thin market can be executed "best" by the rules and still be expensive.
• It does not remove the need for your own judgement about when and how to trade.

Frequently asked questions#

What is best execution?#

A broker's duty to seek the most favourable terms reasonably available for a customer's order, considering price, speed, likelihood of execution, size and cost.

Does commission free trading mean worse execution?#

Not necessarily, but it can. Commission free brokers often earn from order flow, so compare price improvement and execution quality, not just commissions.

How can I tell if my broker gives good execution?#

Compare your fills with the quotes at the time of your orders, track slippage, and review the broker's published routing and execution quality reports.

Sources#

• FINRA, Rule 5310: Best execution and interpositioning
• Wikipedia, Best execution