What it means
When you tap buy in a commission-free app, your order usually does not go to a stock exchange. The broker routes it to a wholesale market maker, which executes it and pays the broker a fraction of a cent per share for the privilege.
That payment is order flow's business model. The wholesaler profits from the spread between the prices where it buys and sells, and it shares a slice with the broker that delivered the order.
The model enabled zero-commission trading. Revenue from order flow replaced per-trade commissions at major retail brokers, opening the stock market to millions of small investors who had been priced out by fees.
The conflict is structural. A broker choosing between two wholesalers might route to the one paying more rather than the one giving customers slightly better prices, which is why regulators police execution quality instead of banning the practice.
In the United States, the Securities and Exchange Commission requires disclosure under Regulation NMS Rule 606: brokers must publish quarterly reports showing where they routed orders and what payments they received, and the SEC's staff guidance explains these duties in detail. Execution quality rules provide the counterweight.
Brokers owe customers best execution, and wholesalers must generally fill retail orders at or better than the public quoted price, with the tiny improvements measured as price improvement statistics. Other countries take a harder line.
The United Kingdom and several European jurisdictions have banned payment for order flow outright, judging the conflict of interest too corrosive to manage with disclosure. For a non-finance reader, the lesson is that free is a pricing strategy, not a gift.
The commission vanished because the orders themselves became the product being sold, and the real question is whether execution quality stays high without the old fee.
In practice
Real-world examples.
Example
A retail investor's market order executes at $50.01 when the public offer was $50.03, a price improvement of $0.02 per share delivered by the wholesaler that paid the broker for the order. On 100 shares that is $2.00 saved against the quote. Brokers must be able to show regulators that such outcomes, not the payments, drive routing choices.
Example
A broker's quarterly Rule 606 report reveals most of its options orders route to one wholesaler, prompting journalists to ask whether payments or execution quality drive the choice. The broker publishes execution statistics to explain its routing. Customers can compare those figures with other brokers.
Example
A UK investor cannot be routed through PFOF arrangements because British rules ban the practice, so her broker charges an explicit commission instead. She sees the cost on her contract note. She compares it with the spread she would otherwise pay.
Formula
Calculation
Broker revenue from PFOF = shares routed x per-share payment, typically fractions of a cent. Customer benefit is measured as price improvement: (public best quote - execution price) x shares executed for a buy order, or the reverse for a sell.
Worked example. A broker routes 2,000,000 shares in a month to a wholesaler paying $0.0015 per share, so its order-flow revenue is 2,000,000 x $0.0015 = $3,000. If those orders received an average price improvement of $0.004 per share, customers together saved 2,000,000 x $0.004 = $8,000 against the public quote, even though they paid no commission.
On a single order, a customer buying 40 shares with $0.004 of improvement per share saves 40 x $0.004 = $0.16, while the wholesaler pays the broker 40 x $0.0015 = $0.06. Whether the arrangement is good for customers depends on how the improvement compares with what a competing route would have delivered, which is what execution-quality statistics try to measure.Case study
Seen in the real world.
This case study is fictional and illustrative. Amara, a made-up nurse in Toronto with a US brokerage account, buys 40 shares of an American company each month through a zero-commission app. Curious about how the service is free, she reads the broker's Rule 606 report and sees that 90% of its stock orders route to two wholesalers paying about $0.0015 per share. She then checks execution quality data showing her orders receive on average $0.004 of price improvement per share against the public quote.
Her rough maths: on a typical $1,200 order of 40 shares, she saves around 40 x $0.004 = 16 cents versus the quoted price and pays no commission, while the wholesaler pays the broker about 40 x $0.0015 = 6 cents. She decides the trade-off is acceptable for her small, patient orders, but moves a planned large purchase to a limit order to control the price precisely. Over a year her 12 orders save about 12 x $0.16 = $1.92 against quotes, which is small, but she compares it with the explicit commission of a rival broker and finds the free route still cheaper for her trading pattern.
Watch out
Common mistakes.
- Believing commission-free means cost-free; the costs move into spreads and routing decisions that are harder to see than a fee line.
- Judging brokers only on PFOF payments instead of execution quality statistics, which show what customers actually received relative to quotes.
- Using large market orders without limit protection in thin stocks, where routing and spread effects dwarf the saved commission.
Questions
People also ask.
Is payment for order flow legal?
Yes in the United States under SEC disclosure and best-execution rules, but it is banned in the United Kingdom and restricted in several other markets.
Does PFOF hurt my trade prices?
Studies generally find small net benefits for small retail orders through price improvement, but the conflict of interest is real, which is why disclosure and best-execution duties exist.
How can I check my broker's arrangements?
Read the broker's quarterly Rule 606 reports, which disclose routing venues and payments, and compare execution quality statistics the wholesalers publish.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%