Internalization is the practice behind most retail stock trades in the United States: when you place an order through your brokerage, your broker-dealer either fills it from its own inventory or hands it to a wholesale market maker that does the same, rather than routing it to a public exchange like the NYSE. Some estimates put the share of retail orders that never reach a public exchange above 90%. Because the firm on the other side of your trade is also the firm you hired to represent you, federal rules impose best execution duties, price improvement expectations, and disclosure requirements meant to keep the arrangement honest. Here is how the mechanics work, where the conflicts sit, and what you can actually see about your own orders.
What Happens When You Place the Order
When you submit a stock order through your brokerage app, it hits the firm’s automated routing system. That system looks at order size, the security, and current market conditions, then decides whether the firm can fill the trade from its own holdings. If the broker has enough shares in its principal account, it steps in as the other side of your trade instead of sending the order to an exchange.
The firm’s matching engine pairs your order against shares it already holds. The whole sequence happens inside the firm’s private network and typically takes milliseconds. Because the trade never touches an exchange, the broker avoids paying exchange access fees, currently capped at $0.003 per share for stocks priced at $1.00 or above under Rule 610 of Regulation NMS. That cap drops to $0.001 per share when amended access fee rules take effect in November 2026.1U.S. Securities and Exchange Commission. SEC Adopts Rules to Amend Minimum Pricing Increments and Access Fee Caps Fractions of a cent per share add up fast when a firm processes millions of orders a day, which is why brokers invest heavily in technology that scans internal inventory before looking elsewhere.
Wholesalers and Payment for Order Flow
Most retail brokers do not internalize orders themselves. They route your orders to a small group of large wholesale market-making firms that specialize in filling retail trades off-exchange. These wholesalers hold deep inventories and use pricing algorithms to take the other side of retail orders at scale. A handful of firms handle the bulk of all retail equity and options order flow in the country.
The link between your retail broker and these wholesalers is payment for order flow. The wholesaler pays your broker a small amount per share or per contract in exchange for receiving your order. That revenue is a significant reason many brokerages can offer commission-free trading. Payment for order flow is legal in the United States, though it has drawn sustained regulatory attention.2U.S. Securities and Exchange Commission. How Does Payment for Order Flow Influence Markets
The core conflict is simple. Your broker has a financial reason to send your order to whichever wholesaler pays the most, not necessarily whichever venue would give you the best price. The SEC has described the problem as a “tension between the firms’ interests in maximizing payment for order flow or trading profits generated from internalizing their customers’ orders, and their fiduciary obligation to route their customers’ orders to the best markets.”3U.S. Securities and Exchange Commission. Special Study: Payment for Order Flow and Internalization in the Options Markets Federal rules do not remove this conflict. They try to manage it through best execution duties and mandatory disclosure.
The Best Execution Duty
Every broker-dealer that internalizes orders or routes them to a wholesaler owes you a duty of best execution. FINRA Rule 5310 requires firms to use “reasonable diligence” to find the best market for your trade and execute it so you get the most favorable price reasonably available.4FINRA. FINRA Rule 5310 – Best Execution and Interpositioning The rule asks not just whether the price was acceptable, but whether the firm looked hard enough.
FINRA lists five factors for judging reasonable diligence:
- Character of the market, including the security’s price, volatility, and available liquidity
- Size and type of transaction, since large orders face different execution challenges than small ones
- Number of markets checked before executing
- Accessibility of the quotation, meaning whether better prices were practically reachable
- Terms of the order, including any specific instructions you gave
Quarterly Execution Reviews
Firms that internalize orders or route them automatically to wholesalers must conduct “regular and rigorous” reviews of execution quality at least quarterly. High-volume firms should review more often.4FINRA. FINRA Rule 5310 – Best Execution and Interpositioning The reviews must be done on a security-by-security and order-type basis, so a firm cannot look at aggregate numbers and move on.
Each review has to evaluate the firm’s current routing against competing venues using several data points: how much price improvement orders received, how often orders got worse prices than the prevailing quotes, the likelihood that limit orders actually executed, execution speed, execution size, transaction costs, customer expectations, and whether payment for order flow arrangements influenced routing decisions. That last factor is notable. FINRA explicitly requires firms to ask whether the money coming in from wholesalers is steering orders away from better venues.
Firms that fall short face FINRA disciplinary actions and SEC enforcement proceedings, and FINRA regularly requires restitution to customers who received inferior executions.
Price Improvement and How It’s Measured
The National Best Bid and Offer, or NBBO, is the highest bid and lowest ask available across all public exchanges at any given moment. When a wholesaler or broker internalizes your order, the NBBO is the measuring stick. A fill at a price better than the NBBO counts as “price improvement,” and that is the primary justification firms offer for keeping orders off public exchanges.
Price improvement is often measured in fractions of a cent. If the best public offer for a stock is $10.01 and the wholesaler fills your buy order at $10.005, you received half a cent of price improvement per share. Internalizers can execute at sub-penny prices even though public exchanges generally cannot quote in sub-penny increments for stocks priced at $1.00 or more.5U.S. Securities and Exchange Commission. FAQ re Rule 612 (Minimum Pricing Increment) of Regulation NMS That asymmetry is part of why wholesalers can consistently offer small price improvements and still profit on the trade.
Regulators measure execution quality using the “effective spread,” which compares the actual trade price to the midpoint of the NBBO at the time the order was received.6U.S. Securities and Exchange Commission. Regulation NMS: Minimum Pricing Increments, Access Fees, and Transparency of Better Priced Orders A narrower effective spread means a better fill. The “realized spread” compares the trade price to the NBBO midpoint some time after the trade, which captures whether the wholesaler’s pricing was genuinely competitive or just looked good in the moment. If a broker internalizes an order without any price improvement, it has to show that other factors like speed or certainty of execution justified keeping the order in-house.
What You Can See About Your Own Orders
Two SEC rules create the transparency framework. Rule 606 governs what your broker tells the public about where it sends orders and how much it gets paid to do so. Rule 605 governs what execution venues, and eventually larger broker-dealers, must report about the quality of their fills.
Rule 606 Order Routing Reports
Every broker-dealer must publish quarterly reports showing where it routes customer orders. The reports must be posted on a freely accessible website and kept available for three years.7U.S. Securities and Exchange Commission. Responses to Frequently Asked Questions Concerning Rule 606 of Regulation NMS They break down routing by stock category (S&P 500 versus other stocks) and by order type (market orders, marketable limit orders, non-marketable limit orders, and others).
For each venue that receives orders, the firm must disclose net aggregate payment for order flow received, any profit-sharing payments, transaction fees paid, and transaction rebates received, reported as both a total dollar amount and on a per-share basis.8eCFR. 17 CFR 242.606 – Disclosure of Order Routing Information Firms also must describe the material aspects of their relationship with each venue, including volume-based payment tiers, minimum order flow agreements, and other arrangements that could influence routing. If you want to know whether your broker is sending orders to the highest bidder, the Rule 606 report is where you look.
A Personalized Report on Your Own Orders
If you place “not held” orders, which give your broker discretion over price and timing, you can request a personalized report covering how your specific orders were routed over the previous six months. The report must list each venue that handled your orders and include the total number of shares the broker executed as principal from its own account, the average net execution fee or rebate per venue, and the average time between order entry and execution measured in milliseconds. That data lets you see whether your broker is making money on the spread between what it pays a venue and what it charges you.
Rule 605 Execution Quality Reports
Rule 605 requires market centers to publish monthly reports on execution quality for covered orders, including price improvement per share and execution speed across different order sizes. Starting August 1, 2026, amended Rule 605 extends that obligation to larger broker-dealers, not just traditional market centers like exchanges.9Federal Register. Extension of Compliance Date for Disclosure of Order Execution Information The amendments also require each reporting entity to produce a summary report alongside the detailed data, which should make it easier to compare execution quality across firms.10U.S. Securities and Exchange Commission. Disclosure of Order Execution Information Previously, a retail broker could internalize millions of orders while only the exchange-level market centers had to publish execution quality data. After August 2026, the brokers themselves will have to show their numbers.
What Changes in Late 2026
The SEC adopted amendments to Regulation NMS in 2024 that reshape the economics of internalization. They take effect on the first business day of November 2026 after the SEC granted temporary exemptive relief pushing back the original compliance date.11U.S. Securities and Exchange Commission. SEC Issues Exemptive Order Regarding Compliance with Certain Rules Under Regulation NMS
Amended Rule 612 introduces variable minimum pricing increments based on how tightly a stock is quoted:
- Stocks with a time-weighted average quoted spread above $0.015: minimum tick stays at $0.01
- Stocks with a time-weighted average quoted spread of $0.015 or less: minimum tick shrinks to $0.005
- Stocks priced below $1.00: minimum tick is $0.0001
Tighter ticks mean public exchanges can quote in smaller increments for heavily traded stocks.12eCFR. 17 CFR 242.612 – Minimum Pricing Increment That narrows the pricing advantage internalizers have enjoyed from being able to offer sub-penny improvement against penny-wide exchange quotes. If exchanges can quote at $0.005 increments, a wholesaler offering $0.001 of improvement is working with thinner margins.
At the same time, amended Rule 610 cuts the maximum access fee for protected quotations from $0.003 to $0.001 per share for stocks priced at $1.00 or above. Lower exchange fees reduce one of the cost advantages that made internalization attractive in the first place. Whether the combined effect of tighter ticks and lower fees meaningfully shifts order flow back to public exchanges is still an open question.