The Price of Free Trading: What Is Payment for Order Flow?
When your broker charges you nothing to buy a stock, someone else is paying. Here is who, how much, and what it means for the price you actually get.
Commission-free trading feels like a straightforward win for ordinary investors. No fees to buy a stock. No fees to sell it. Keep all the gains. The reality is more complicated, and understanding the mechanism behind free trading changes how you think about who your broker is actually working for.
The mechanism is called payment for order flow. In 2025, the industry paid $4.8 billion through this arrangement. The European Union banned it outright. The United States still permits it. And the firm at the centre of it, Citadel Securities, processes a substantial share of all retail equity trades in the country.
The Price of Free Trading: What Is Payment for Order Flow? //Peiid
How It Works
When you place a trade through a retail broker, the broker has a choice about where to send your order. It can route it to a public stock exchange, where your buy order gets matched with someone else’s sell order at whatever price the market determines. Or it can route it to a market maker, a firm that stands ready to buy and sell securities continuously, profiting from the difference between the prices at which it buys and sells.
Market makers pay brokers for the privilege of receiving their customers’ orders. This is payment for order flow. Citadel Securities, the largest market maker in US equities, pays fees to Robinhood and other retail brokers every time those brokers send a customer trade their way.
The broker benefits because those payments fund the commission-free model. Robinhood made $687 million from selling order flow in 2020, representing 81% of its total revenue. In the first quarter of 2021, at the height of the GameStop frenzy, it made $331 million from the arrangement in a single quarter.
The market maker benefits because seeing large volumes of retail order flow gives it information about supply and demand that it can use in its trading. It also profits from the spread on each trade it executes.
What the Customer Gets
The industry’s argument for payment for order flow is that retail investors receive price improvement: the market maker fills your order at a slightly better price than the public exchange would have offered, and pockets the difference between that improvement and the public exchange price. You get a marginally better execution. They get paid for providing it.
For most retail trades in large, liquid stocks, the practical impact is small. Research suggests the difference amounts to roughly one to three dollars per hundred shares traded for equities. The effect is more significant in options, where poor execution can cost considerably more.
The counterargument is about conflict of interest rather than execution quality. When a broker is paid by a market maker to route orders to them, the broker’s financial incentive is to maximise payment for order flow revenue rather than to find the best possible execution for the customer. Whether those two things always align is the question regulators have been asking for years.
The GameStop Moment
Payment for order flow became widely known during the GameStop trading frenzy of January 2021, and not for flattering reasons.
GameStop, a struggling video game retailer, became the target of a coordinated buying campaign by retail investors on Reddit’s WallStreetBets community, who noticed that hedge funds had taken enormous short positions against the stock. As retail buying pushed the price up, short sellers faced massive losses. Melvin Capital, one of the largest short sellers, required a $2.75 billion emergency bailout.
Citadel, which was both Robinhood’s largest payment for order flow partner and one of the firms that provided capital to bail out Melvin Capital, found itself at the centre of a controversy it denied creating. When Robinhood abruptly restricted purchases of GameStop shares on January 28, citing capital requirements, critics alleged that Citadel had pressured Robinhood to act in order to protect its investment in Melvin Capital.
Both firms denied any coordination. Robinhood’s CEO, Citadel’s Ken Griffin, and the Reddit user who had helped ignite the frenzy all testified before Congress in February 2021. No evidence of direct coordination between Citadel and Robinhood’s trading halt decision was produced. But the episode made visible a web of financial relationships that most retail investors had not previously considered.
Where It Stands Now
Payment for order flow remains legal in the United States as of 2026. The SEC under previous leadership considered banning or restricting it but did not act decisively. Regulatory pressure continues, but the practice is now so embedded in the economics of retail brokerage that eliminating it would require a fundamental restructuring of how commission-free trading is funded.
The European Union took a firmer position. Payment for order flow is banned across EU member states, meaning European retail investors’ orders must be routed to public exchanges rather than to market makers paying for access. Whether this produces meaningfully better outcomes for investors is still debated — execution quality on public exchanges is not automatically superior in every case.
For retail investors in the US, the practical implication is narrower than the controversy suggests. For most trades in major stocks, the execution difference between payment for order flow and a public exchange is small. For options traders or those trading less liquid securities, it can be more significant.
The more important point is structural. Your broker’s interests and your interests are not perfectly aligned when the broker is paid by a third party for access to your trades. Understanding that does not necessarily mean changing how you invest. It does mean understanding what “free” actually costs.
Key Takeaways
- Payment for order flow is the practice of market makers paying retail brokers to route customer orders to them rather than to public exchanges.
- The US retail brokerage industry received $4.8 billion in payment for order flow in 2025. Robinhood made 81% of its 2020 revenue from the arrangement.
- Citadel Securities is the largest participant, processing a substantial share of US retail equity volume and paying brokers including Robinhood for their order flow.
- The EU banned payment for order flow. It remains legal in the United States.
- The practical impact on execution quality for most retail investors is small but present. The more significant issue is the conflict of interest between a broker paid by a market maker and the customer whose orders they route.