Brokerage Rule 606 That Routes Your Buy Order to a Firm Paying for the Privilege

You click 'buy' on your brokerage app. In under a second, the order leaves your account. But it doesn't head straight to the New York Stock Exchange or Nasdaq. Instead, it takes a detour—to a private firm that pays your broker for the right to fill it. That detour is the hidden plumbing of modern retail investing, and it's governed by a little-known SEC rule called Rule 606.

Your Buy Order Just Took a Detour

When you place a marketable order—a buy at the ask or a sell at the bid—your broker decides where to send it. The destination could be a public exchange like NYSE or Nasdaq, an alternative trading system (ATS), or a 'wholesaler' such as Citadel Securities or Virtu Financial. Wholesalers are high-frequency trading firms that buy retail order flow in bulk.

Why would a broker send your order to a wholesaler instead of the exchange? Money. Wholesalers pay brokers for the right to execute those orders, a practice known as payment for order flow (PFOF). The payments are tiny—often a fraction of a cent per share—but they add up. In 2020, Robinhood earned roughly $687 million from PFOF, according to SEC filings. That revenue stream allowed the firm to offer zero-commission trading.

Rule 606, adopted by the SEC in 2000 and amended in 2018, requires brokers to publish quarterly reports showing the percentage of orders routed to each venue. You can find these reports on your broker's website, though they're often buried in the fine print. The rule was designed to shed light on routing practices, but critics say it doesn't go far enough.

The detour matters because it affects the price you pay. When a wholesaler fills your order, it may offer 'price improvement'—a slightly better price than the public quote. But the wholesaler also profits from the spread, and some studies argue that retail investors lose billions each year due to inferior execution. The trade-off between commission-free trading and order-flow revenue is the central tension in modern brokerage.

Payment for Order Flow: The Kickback That Built Modern Brokerage

Payment for order flow isn't new. It existed in the 1990s, when brokers like Datek and Ameritrade used it to offer low-cost trades. But it exploded after 2019, when several major brokers—including Robinhood, Schwab, and E*Trade—slashed commissions to zero. With commissions gone, PFOF became the primary revenue source for many retail brokers.

Two firms dominate the wholesale market: Citadel Securities and Virtu Financial. As of late 2024, Citadel Securities handled roughly 40% of all U.S. retail order flow, according to industry estimates. Virtu handled another 20–25%. These firms use speed and data to profit from the bid-ask spread. When a retail investor sells a stock at $10.00, the wholesaler may buy it at $10.00 and sell it a moment later at $10.01—earning a penny per share.

The conflict of interest is obvious: your broker has an incentive to route orders to the wholesaler that pays the most, not necessarily the one that gets you the best price. In 2020, the SEC fined Robinhood $65 million for misleading customers about its PFOF practices, including failing to disclose that it routed orders to firms that paid more, even when that meant worse execution.

Proponents argue that PFOF benefits retail investors by enabling commission-free trading and, in many cases, providing price improvement. A 2020 study by the SEC's Division of Economic and Risk Analysis found that retail marketable orders executed by wholesalers often received prices better than the national best bid or offer (NBBO). But the improvement was small—typically less than a tenth of a cent per share.

Critics counter that the conflict is structural. As former SEC Commissioner Robert Jackson put it in a 2021 speech, 'When your broker gets paid for sending your order to a particular firm, you have to wonder: whose interests is my broker serving?' The debate has led to regulatory proposals in the U.S. and outright bans abroad.

Rule 606 Reports: What They Disclose and What They Hide

Rule 606 reports are supposed to bring transparency to order routing. Each quarter, brokers must file a public report listing the percentage of non-directed orders—those where the broker chooses the venue—routed to each execution venue. The report also shows the net payments received from each venue, broken down by order type (marketable, limit, etc.).

But the reports have serious limitations. First, they aggregate data across all customers and all stocks. You can't see where your specific order went, or whether you got a good fill. Second, the reports don't include execution quality metrics like price improvement or fill rate. A broker could route 90% of orders to a wholesaler that pays well but offers poor execution, and the report wouldn't flag it.

The SEC recognized these gaps and, in 2018, adopted Rule 606(b)(3), which requires brokers to provide a more detailed report upon request. That report must include the venue that executed each order, the price received, and the amount of price improvement. But few investors request it, and the data is not standardized, making comparisons difficult.

Some brokers make the reports easy to find. Fidelity, for example, posts its Rule 606 report prominently on its website. Others bury them in legal disclosures. Robinhood's 2024 Q1 report, for instance, was tucked inside a PDF linked from a page titled 'SEC Reports'—not exactly a place most customers browse.

Even if you find the report, interpreting it requires effort. The reports use jargon like 'net liquidity rebates' and 'execution venue' and lump together orders of all sizes. For a typical retail investor, the takeaway is often: your broker sends most orders to a handful of wholesalers, and it gets paid for doing so. The details of what that means for your pocket remain opaque.

How Wholesalers Profit from Your Order Flow

Wholesalers like Citadel Securities and Virtu Financial operate as market makers. They buy and sell stocks from their own inventory, profiting from the spread between bid and ask prices. When a retail order arrives, the wholesaler can fill it immediately—often at a price slightly better than the public quote—because it holds a large inventory of shares.

The key to their profitability is information. Wholesalers see the entire flow of retail orders, which gives them a sense of where the market is heading. They also have access to high-speed data feeds and co-located servers that let them trade faster than almost anyone else. This speed advantage allows them to adjust prices before the broader market reacts.

Consider a simple example: You want to buy 100 shares of Apple at the market price. The current NBBO shows an ask of $150.00. The wholesaler may fill your order at $149.99—a penny of price improvement. But the wholesaler also buys Apple shares from other customers at $149.98 and sells them to you at $149.99, pocketing the penny. On a single trade, that's a dollar. On millions of trades per day, it adds up to billions.

A 2023 study by researchers at the University of Chicago and the SEC estimated that retail investors lost roughly $1.5 billion per year due to suboptimal execution in options markets alone. For stocks, the losses are harder to quantify but likely significant. The study found that wholesalers earned about $0.85 per $100 traded in options, with much of that coming from the spread.

Wholesalers defend their role by pointing to the price improvement they provide. In a 2021 blog post, Citadel Securities claimed that it improved prices for retail investors on 99% of marketable orders, saving them over $1 billion annually. But critics note that the improvement is measured against the NBBO, which itself may be stale or manipulated. In fast-moving markets, the price you get may be worse than what you could have gotten on an exchange.

Price Improvement: The Trade-Off You Rarely See

Price improvement is the wholesaler's main selling point. When a retail order arrives, the wholesaler may fill it at a price better than the current best bid or offer. For a market order to buy, that means paying less than the ask; for a sell, receiving more than the bid. In theory, this benefits the retail investor.

But the size of that improvement is often tiny. The SEC's 2020 study found that for marketable orders in stocks, the average price improvement was about $0.0008 per share—less than a tenth of a cent. For a 100-share trade, that's eight cents. Meanwhile, the wholesaler's profit on the spread might be several cents per share. The net effect is that the investor gets a small benefit while the wholesaler captures a larger one.

In volatile markets, the improvement can disappear entirely. If a stock is moving quickly, the NBBO may change before the wholesaler can fill the order. The wholesaler may still offer a price, but it may be worse than the original quote. Studies have shown that during periods of high volatility, retail execution quality deteriorates relative to institutional trades.

The SEC's 2020 pilot program on tick sizes—which tested the effects of wider spreads—found mixed results for retail execution. In some cases, wider spreads led to better price improvement; in others, they increased wholesaler profits without benefiting investors. The pilot highlighted how complex the trade-offs are.

Academic research suggests that the net cost of PFOF to retail investors is positive when you account for the spread and the opportunity cost of not trading on exchanges. A 2022 paper by economists at the University of California estimated that retail investors pay an implicit cost of roughly $0.02 per share in stocks and $0.50 per contract in options due to PFOF. For active traders, those costs add up.

The EU and UK Took a Different Path

While the U.S. has allowed PFOF to flourish, most other major markets have restricted or banned it. The European Union's Markets in Financial Instruments Directive II (MiFID II), which took effect in 2018, effectively banned payment for order flow by requiring brokers to disclose and justify any inducements. In practice, few EU brokers accept PFOF.

The United Kingdom has gone further. In 2021, the Financial Conduct Authority (FCA) proposed a ban on PFOF, citing conflicts of interest and harm to retail investors. The ban took effect in 2023, making the UK one of the strictest regulators on this issue. Canada and Australia also prohibit or heavily restrict PFOF.

The U.S. remains an outlier. The SEC under Chair Gary Gensler has proposed changes to market structure, including a rule that would require brokers to compete for retail orders via auctions rather than routing them to wholesalers. As of late 2024, that proposal has not been adopted, and industry lobbying remains intense.

For cross-border investors, the regulatory divergence creates complications. A U.S. citizen living in Europe may find that their U.S. broker still routes orders through PFOF, while a European broker cannot. The differences in execution quality and cost can be significant, though they are rarely disclosed to the investor.

The global trend is moving away from PFOF, but the U.S. market's size and influence mean that change, if it comes, will be slow. Until then, retail investors in the U.S. must navigate a system where their broker's interests are not fully aligned with their own.

What You Can Actually Do About It

If you want to avoid PFOF, the simplest step is to choose a broker that doesn't accept it. As of 2024, Fidelity and Schwab do not accept payment for order flow for stocks and ETFs. Fidelity, in particular, has a policy of routing orders to venues that provide the best execution, regardless of payments. Other brokers, like Vanguard and Merrill Edge, also avoid PFOF.

Using limit orders instead of market orders can also help. A limit order specifies the maximum price you're willing to pay (for a buy) or the minimum you'll accept (for a sell). Limit orders are less attractive to wholesalers because they don't guarantee execution, but they can reduce the cost of the spread. In some cases, limit orders are routed to exchanges where they may get better fills.

Check your broker's Rule 606 report. It's usually available in the legal or disclosures section of the website. Look for the percentage of orders routed to wholesalers and the net payments received. If a large share goes to a single wholesaler, that's a red flag. You can also compare reports across brokers to see which ones rely more on PFOF.

For larger trades—say, over $10,000—consider using a broker that offers direct exchange routing. Some brokers, like Interactive Brokers, allow you to choose the routing venue. You may pay a small commission, but you'll get direct access to the market without a wholesaler in the middle.

Finally, the SEC provides a public database of execution quality reports, known as Rule 605 reports. These show, for each exchange and wholesaler, statistics on fill rates, price improvement, and effective spreads. Comparing these reports can give you a sense of which venues perform best. But the data is dense and requires some effort to interpret.

None of these steps will eliminate the hidden costs of trading entirely. The system is designed to be opaque, and even the most diligent investor can't fully untangle the web of payments and incentives. But understanding the rules—and knowing where your order goes—is the first step to making informed choices.

This article is for informational purposes only and does not constitute personalized investment advice. Consult a qualified financial professional before making trading decisions.