A market maker makes money mainly by capturing the small gap between the price at which it buys a stock and the slightly higher price at which it sells it, then repeating that trade millions of times a day. That gap, the bid-ask spread, might be half a penny on an actively traded name, but at scale it produces billions in annual revenue. Layered on top are exchange rebates, payments from brokers for sending in retail orders, and small profits from pricing differences across trading venues. Each of those streams carries real risk, and recent SEC rule changes to tick sizes and exchange fee caps have reshaped the math heading into 2026.
The Bid-Ask Spread Is the Core Mechanic
At any moment, a stock has two prices on an exchange: the bid, which is the most the market maker will pay to buy, and the ask, which is the least it will take to sell. The difference is the spread. When one investor sells at the bid and another buys at the ask, the market maker collects that difference as gross profit. If the bid is $50.00 and the ask is $50.05, the nickel per share is the firm’s compensation for standing ready to trade both sides.
How narrow a spread can go depends on SEC rules on minimum price increments. Under Regulation NMS Rule 612, stocks priced at $1.00 or above were historically quoted in minimum increments of one cent. That changed in November 2025, when amended Rule 612 introduced a half-penny increment ($0.005) for stocks whose time-weighted average quoted spread is $0.015 or less. Stocks with wider average spreads keep the one-cent minimum.1Federal Register. Regulation NMS: Minimum Pricing Increments, Access Fees, and Transparency of Better Priced Orders For the most heavily traded names, the smallest possible spread shrank from a penny to half a penny, compressing the profit the firm can capture on each round trip.
Spread profit only lands if the firm can unload its inventory before the price moves against it. Buy at $50.00, watch the market drop to $49.90 before you sell, and the spread is irrelevant: the loss on the position swallows it. Market makers manage this by staying close to flat, buying and selling in roughly equal amounts so they are not sitting on big directional bets. They also adjust quotes in real time against the National Best Bid and Offer to stay competitive without taking on extra exposure. FINRA Rule 5310 reinforces the dynamic by requiring broker-dealers to seek the best available prices for customer orders, which keeps spreads from widening beyond what competition allows.2FINRA.org. 5310 – Best Execution and Interpositioning
Why Retail Orders Are the Prize
Market makers rarely execute retail orders at the public bid or ask. They fill them at prices between the two, giving the investor a better deal than the quoted spread. A stock quoted at $50.00 bid and $50.05 ask on the public exchange might have a retail buy filled at $50.03 by a wholesaler, saving the customer two cents a share while the firm still captures three cents if the offsetting sell comes in at $50.00. That practice, called price improvement, returned an estimated $3 billion to retail investors in 2022, with roughly half the spread going to the investor and half to the firm.
Price improvement is calculated self-interest. Retail investors trade in small sizes and predictable patterns, without the market-moving information that often sits behind institutional orders. By offering slightly better prices, a market maker attracts a steady stream of this low-risk flow, which is far easier to profit from than trading against institutional algorithms. To secure that flow directly, many market makers pay retail brokerages to route customer trades to their systems. This is payment for order flow. The broker gets a small per-share or per-contract fee, and for options, these payments have historically ranged from around $0.25 to over $1.00 per contract.3U.S. Securities & Exchange Commission. Special Study: Payment for Order Flow and Internalization in the Options Markets
Brokers must disclose these arrangements. SEC Rule 606 requires every broker-dealer to publish quarterly reports showing where it routes customer orders and what financial inducements it receives from each venue.4eCFR. 17 CFR 242.606 – Disclosure of Order Routing Information Starting in August 2026, updated Rule 605 reporting requirements will force market makers and brokers to publish more granular execution-quality statistics, including price improvement measured against the best available displayed price, giving the public a clearer picture of which routing choices are actually delivering competitive fills.5Federal Register. Extension of Compliance Date for Disclosure of Order Execution Information
Exchange Rebates Add a Second Layer
Most electronic exchanges run on a maker-taker pricing model. They pay a small rebate to anyone who posts a resting limit order that adds liquidity, and they charge a fee to whoever trades against that order and removes liquidity. For years, the standard taker fee sat at the regulatory maximum of $0.003 per share, with maker rebates around $0.002.6SEC.gov. Maker-Taker Fees on Equities Exchanges – Memorandum
That math changed in November 2025 when amended Rule 610 of Regulation NMS cut the maximum access fee to $0.001 per share for stocks priced at $1.00 or more.7U.S. Securities and Exchange Commission. SEC Adopts Rules to Amend Minimum Pricing Increments and Access Fee Caps and to Enhance the Transparency of Better Priced Orders Because exchanges fund rebates out of the fees they collect from takers, the lower cap compressed rebates as well. A firm can no longer count on picking up $0.002 per share just for posting a quote. Rebate income is smaller now, but it still functions as a cushion: a firm might break even on the trade price itself and still pocket the exchange rebate. Across billions of shares a month, fractions of a tenth of a cent add up.
Arbitrage and Inventory Hedging
Because U.S. equities trade across more than a dozen exchanges and alternative trading systems, the same stock can be priced slightly differently in two places for a fraction of a second. Market makers use high-speed connections to buy at the lower price on one venue and sell at the higher on another, earning a low-risk profit while also correcting the inconsistency for everyone else. These cross-venue trades fill in around the edges of the main spread business.
Inventory management is less a revenue stream than a defense. A firm that bought and sold all day without watching its accumulated positions would be making a leveraged bet on the market. When inventory builds up on one side, the firm shifts quotes to pull the position back toward neutral, lowering the ask to attract buyers or lowering the bid to discourage sellers. In options market making, where prices move nonlinearly against the underlying stock, firms hedge by holding an offsetting position in the stock sized to the option’s delta, and adjust that hedge continuously as the stock moves.
What Eats the Profits
The spread looks like guaranteed money until you meet the trades that wipe it out. The biggest everyday threat is adverse selection: the person on the other side of the trade sometimes knows more than the market maker does. When an institutional investor with proprietary research hits a quote, the price tends to keep moving in the direction of that trade. The firm bought at $50.00 expecting to sell at $50.05, but by the time it turns around, the stock is at $49.85. Most of the daily damage happens here, and it’s the reason firms pay so aggressively for retail flow, which carries much less adverse-selection risk.
Extreme volatility is a different problem. During rapid sell-offs, the value of inventory can drop faster than the firm can unload it, and hedge-ratio models start to break down when prices gap rather than glide. Quoting obligations have historically been loose enough that firms could effectively step away during the worst moments by posting very wide quotes. Regulators tightened some standards after the 2010 flash crash, but the tension between requiring firms to trade during panics and letting them manage their own survival has not been fully resolved.
Those risks are why market making is not simply standing between buyers and sellers and printing money. The firms that last run risk systems that score each incoming order for its likelihood of carrying adverse information, adjust position limits in real time, and know when to widen quotes or pull back rather than take on more exposure.
The Cost of Being in the Game
Half a penny per share is not a business model until you multiply it by millions of trades a day, and reaching that volume carries heavy fixed costs. To compete, a market maker needs servers physically housed inside the exchange’s own data center, an arrangement called co-location. On Nasdaq alone, a full server cabinet runs $5,490 per month, a 10-gigabit fiber connection to the exchange runs $11,000 per month, and wireless market data feeds for a single exchange can exceed $25,000 monthly.8The Nasdaq Stock Market. Nasdaq General 8 Connectivity Multiply that across every exchange and data source the firm touches, add the proprietary algorithms making decisions in microseconds, and technology alone runs into tens of millions a year.
Capital rules sit on top of the technology bill. Under the SEC’s Net Capital Rule, a market maker must maintain at least $2,500 in net capital for each stock in which it makes a market, or $1,000 per stock if the stock trades at $5.00 or below, with the per-security requirement capped at $1,000,000 in total. Firms that clear through another broker-dealer rather than self-clearing must keep liquidating equity equal to at least 25 percent of the market value of their long positions and 30 percent of their short positions.9eCFR. 17 CFR 240.15c3-1 – Net Capital Requirements for Brokers or Dealers Whatever the spreads, rebates, order-flow payments, and arbitrage trades produce, that income has to clear all of this before any of it becomes profit.