A zero-commission trade is not free. The cost has moved from a visible commission line to the price at which your order gets filled. Payment for order flow (PFOF) is the mechanism behind that shift, and understanding it tells you more about your broker than any marketing page will.
The short version: your broker sends your order to a market maker or exchange instead of to a public market itself. The market maker pays the broker for that flow, then earns the difference between the price it buys at and the price it sells at. You never see an invoice. You may still pay, in fills that are a fraction worse than the best available price.
What payment for order flow actually is
When you tap buy on a brokerage app, the order does not automatically travel to the New York Stock Exchange or Nasdaq. Most retail brokers route it to a wholesaler, a firm that holds inventory in the stock and stands ready to trade against you. Citadel Securities, Virtu, Jane Street and similar firms dominate this business in US equities.
The wholesaler pays the broker a small fee per share, typically a fraction of a cent. That fee is the payment for order flow. The broker keeps it, and in exchange gives the wholesaler the right to execute your order. The wholesaler fills you at or slightly inside the national best bid and offer, then manages the position and the spread.
This is legal in the US under SEC rules, provided the broker routes in a way that serves the customer’s best interest and discloses the arrangement. It is restricted for retail orders in the UK and the wider European Union, which is why “commission-free” looks different on each side of the Atlantic.
Where the money comes from
A market maker earns in two main ways. The first is the spread: the gap between what it pays to buy and what it charges to sell. On a liquid large-cap stock that gap is tiny, often a cent or less. On a thin small-cap it can be wide enough to matter a lot.
The second source of revenue is inventory management. The wholesaler takes the other side of your trade and later unwinds the position, hopefully at a better price. It also earns rebates from exchanges on some orders, while profiting from the information embedded in the flow itself—retail orders tend to be small and uninformed relative to institutional ones.
For the broker, PFOF is revenue. A high-volume retail broker with millions of daily trades can collect meaningful sums without charging you a cent. That revenue subsidizes the app, the customer service and the marketing. It also creates an incentive to maximize order flow, which is where the conflict of interest sits.
Execution quality: the part that affects your fill
The regulatory test in the US is “best execution,” but it does not mean you get the single best price across every venue at that instant. It means the broker has policies reasonably designed to get you favorable terms, and it must review execution quality regularly. That is a lower bar than most retail traders assume.
Price improvement is the counter-argument worth taking seriously. Wholesalers often fill retail orders at a price better than the displayed best bid or offer, and studies funded by the industry argue retail investors get better fills than they would on public exchanges. Independent academic work has found mixed results depending on order size and stock. The honest position is that PFOF can produce good fills for small orders in liquid stocks, and worse outcomes in less liquid names where the spread is wide.
What you can check are your broker’s SEC Rule 606 reports, which disclose routing venues and PFOF received, along with Rule 605 execution quality statistics. These are public. If your broker does not make them easy to find, that tells you something.
The UK and EU picture
The UK’s Financial Conduct Authority banned PFOF for retail clients., and MiFID II extended a similar ban across the EU. UK brokers therefore cannot take payment for routing your order. They monetize differently: wider spreads on their own quotes, currency conversion charges, platform fees, or interest on cash balances.
That does not make UK brokers cheaper. A “free” share dealing account may quote you a spread that is wider than the underlying market, so the cost lands in the same place as PFOF: in the execution. The mechanism differs, yet the economic question is identical. Ask what your broker earns when you trade, and from whom.
What this means for traders
If you trade over weeks to a few months, execution cost compounds quickly. A fraction of a cent per share sounds trivial until you trade size or trade often. For active traders, the relevant comparison is total cost per round trip, not the headline commission.
Watch limit orders. A market order handed to a wholesaler has no price protection beyond the broker’s routing logic. A limit order sets your floor or ceiling and removes the worst-case fill from the equation. On less liquid stocks, the difference between a marketable limit and a plain market order can exceed any commission you thought you saved.
Also check whether your broker sells its own order flow data or routes to an affiliated market maker. Vertical integration, where the broker and the executing venue share ownership, is legal but deserves scrutiny. Read the 606 report for the venues your orders actually reach.
What this means for longer-term investors
If you trade infrequently, PFOF is a relatively minor cost factor compared to other considerations. A few cents of spread on a position you keep for years is noise compared with fees, fund expense ratios and tax treatment. Do not let the debate distract you from those.
The practical concern for investors is different, since fractional shares, automatic dividend reinvestment and recurring buys all generate order flow, while the routing behind them is usually invisible. Therefore, check that your broker’s execution statistics cover the order types you actually use. If you invest through a UK or EU broker, the equivalent check is the all-in cost disclosure you receive before trading, which should show the spread and any platform charge.
Regulation and what is changing
The SEC proposed major changes to equity market structure in recent years, including an order competition rule that would have pushed more retail orders into competitive auctions. The proposal was withdrawn before adoption, and the current direction of US rulemaking is less restrictive. Do not assume the rules you read about today will be the rules next year.
In the UK, the FCA has consulted on whether to allow some form of PFOF as part of its push to simplify retail disclosure and encourage investment. That is a live policy question, not settled law. If the ban is relaxed, UK brokers could adopt the US model, and the execution-quality questions above would apply directly.
For your own decisions, the stable facts are these: PFOF is disclosed in the US, banned for retail in the UK and EU, and the economic cost shows up in fills rather than fees. Regulation changes the paperwork, not the underlying trade-off.
Conclusion: read the routing, not the marketing
Free trading is a pricing decision, not a gift. In the US, your broker is paid to send your order somewhere, and the quality of that somewhere determines what you actually pay. In the UK, the payment is banned but the cost still exists, hidden in spreads and platform charges.
The useful habit is to ask two questions before you fund an account: what does this broker earn when I trade, and where do my orders go? The answers are in regulatory filings, not in the app’s welcome screen. Check them once, then check again when your trading frequency or order size changes.
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Frequently Asked Questions
Is payment for order flow legal?
Yes in the US, where the SEC permits it with disclosure and best-execution obligations. It is banned for retail clients in the UK and the EU, so brokers there monetize through spreads, platform fees and currency charges instead.
Does payment for order flow make my trades worse?
It can, but not automatically. Wholesalers often fill small retail orders at or better than the displayed best price in liquid stocks. The risk is larger in wide-spread, less liquid names, where the spread cost can exceed what a commission would have been.
How can I check my broker's execution quality?
US brokers must publish SEC Rule 606 routing reports and Rule 605 execution statistics. Look at which venues receive your order types and the price improvement figures, then compare across brokers you are considering.
Why do UK brokers not charge commissions if PFOF is banned?
They earn from other sources: wider spreads on their own quotes, foreign exchange conversion, platform or account fees, and interest on client cash. The cost is still there, just not labeled as a commission.
Should I use limit orders to avoid PFOF costs?
Limit orders give you price protection that market orders lack, especially in less liquid stocks. They do not eliminate PFOF, since the order can still be routed to a wholesaler, but they cap the worst fill you can receive.
This article is for general information only and does not constitute investment advice. Always do your own research before making trading decisions.