A market maker is a firm or individual that constantly posts buy and sell prices for a security and agrees to trade at those prices. The point is to keep trading available even when natural buyers and sellers do not line up at the same time.
By quoting both a bid and an offer, the market maker supplies liquidity, helps price discovery and fills customer orders. The compensation is the bid‑ask spread and, on some venues, small fee rebates, balanced against the risk of holding inventory while prices move.
How a market maker works in practice
At any moment the market maker submits two limit orders: a bid to buy and an offer to sell. Each quote has a price and a size. If a buyer hits the offer, the market maker sells from its inventory. If a seller hits the bid, it buys and adds to its inventory. Quotes are updated constantly as prices move and as the firm manages risk.
Good market makers try to keep their inventory near target levels, so they adjust quotes to encourage the flow they want. If they are long too many shares, they may shade the offer lower or the bid lower to attract sellers. If they are short, they may adjust the other way to draw in buyers. They also hedge. Equity market makers might use index futures or options to offset exposure. Options market makers often delta‑hedge with the underlying shares.
On many exchanges, registered market makers have obligations. Typical requirements include quoting during most of the session, staying within a maximum spread and offering a minimum size. The details vary by venue and by instrument. In very volatile conditions some obligations can be relaxed or temporarily suspended.
Where you will encounter market makers
- Listed shares and ETFs. Exchanges appoint or register firms to quote continuously and to support opening and closing auctions. Some venues also have designated market makers for each symbol.
- Options on shares and indices. Multiple competing market makers stream quotes for many strikes and expiries, which is why options often show many bid and ask pairs at once.
- Bonds and OTC products. Dealers act as market makers over the phone or on electronic request‑for‑quote systems. Prices are firm only for a stated size and time.
- Foreign exchange. Dealer banks and electronic liquidity providers quote two‑way prices to clients and on matching systems around the clock.
- Crypto. Centralised exchanges rely on market‑making firms to keep order books tight. In decentralised finance, an automated market maker is a different model that uses liquidity pools and formulas rather than quoted two‑way prices.
How they make money and what can go wrong
Revenue usually comes from capturing part of the spread many times a day. On some venues there are maker‑taker fees, where posting visible orders may earn a small rebate. Wholesale market makers that interact with retail brokers can also benefit from order flow that is cheaper to trade against than the public order book, subject to best‑execution rules that vary by jurisdiction and can change.
Against that income sit several risks and costs:
- Adverse selection. When informed traders buy just before good news or sell just before bad news, the market maker ends up on the wrong side.
- Inventory risk. Holding stock while prices swing can create losses before the position is hedged or unwound.
- Volatility and gaps. Sudden moves widen spreads and can blow through quotes before they update, especially around auctions or halts.
- Hedging costs. Futures, options or borrowing stock to short all come with fees and slippage.
- Technology and competition. Many market makers are highly automated, often grouped with high frequency trading firms. Faster rivals can win the same trades or reprice sooner when conditions change.
What those quotes on your screen mean
The bid is the highest price someone is currently willing to pay. The offer, or ask, is the lowest price someone is willing to accept. The bid‑ask spread is the gap between them. The size tells you how many shares or contracts are available at that price from the quoting participants.
Level 1 screens usually show the best bid and best offer at your chosen venue, and on some systems a consolidated best across venues. Level 2 depth shows multiple price levels and sizes. When spreads are tight and there is depth at several prices, trading is easier and cheaper. When spreads widen and depth thins out, expect more slippage.
Many market makers quote in small visible sizes and refresh quickly after fills, which is normal. It helps them manage risk and adapt to flow. If you see frequent tiny price updates, that is quotes being revised as the firm reacts to new market data and its changing inventory.
Market maker vs broker, dealer and automated market maker
- Broker. Routes your order to a venue or dealer, often adding smart logic to seek the best price. A broker is your agent and does not usually take the other side.
- Dealer. Trades on its own account. A market maker is a type of dealer that commits to quoting two‑way prices on a regular basis.
- Exchange or ECN. Matches buyers and sellers under set rules. It is not the counterparty to your trade, it is the venue.
- Automated market maker in DeFi. A smart contract that sets prices by a formula using pooled liquidity. It is not quoting a bid and an offer in the traditional sense, and prices adjust as the pool balance changes.
A quick example: quotes, fills and inventory
Imagine a stock trading around 100.00. A market maker quotes 99.98 to buy 2,000 shares and 100.02 to sell 2,000. A customer sends a market order to buy 1,500 shares. The market maker sells those 1,500 at 100.02, reducing any long inventory or going short by 1,500 if it had none. It has earned 4 cents per share relative to its bid, before hedging and costs.
Now the price blips up to 100.10. If the market maker is short 1,500, it faces a loss if it buys back at the higher level. It may hedge by buying futures or by raising its quotes to 100.04 by 100.08 to attract sellers. If sellers arrive and it buys 1,500 at 100.04, it has covered the short and locked in a 2 cent loss on that round trip, partly offset by any earlier spread income.
Over a day, results are the sum of many such micro‑trades. When spreads are tight and flow is balanced, profits come from a high volume of small edges. When the market lurches or informed flow dominates, losses can mount quickly. That is why risk limits, fast pricing models and disciplined inventory control sit at the centre of market making.