How do stock exchanges work, and what happens after you press buy?

What is a stock exchange?#

The SEC's investor site defines securities exchanges as markets where securities are bought and sold^[1]. An exchange does not own the shares or set their value. It provides the rules and the matching system that let millions of buyers and sellers find each other at an agreed price.

In the U.S., a national securities exchange is one that has registered with the SEC under Section 6 of the Securities Exchange Act of 1934^[2]. The SEC's list, last updated in January 2026, includes familiar names such as the New York Stock Exchange and The Nasdaq Stock Market, along with Cboe, NYSE Arca, Investors Exchange, MEMX and the Texas Stock Exchange — more than 20 exchanges in all^[2]. Rules differ by country; other markets have their own exchanges and regulators.

Exchanges also set standards for the companies they list. FINRA notes that companies listing on Nasdaq, the NYSE, Cboe or other registered national exchanges generally have to meet defined quantitative standards^[3]. Stocks that are not listed may be quoted over the counter instead, and many of those trade infrequently and can be hard to sell^[3].

How did today's exchanges come about?#

The oldest U.S. exchange started with a handshake agreement. Today's trading is mostly electronic, but the basic job — matching buyers and sellers — has not changed.

1. 1792

   The NYSE traces its origins to the Buttonwood Agreement, signed by 24 stockbrokers on May 17, 1792^[4].

2. 1971

   Nasdaq is founded as the world's first fully electronic quotation system^[5].

3. 2005

   The NYSE launches its Hybrid Market, a blend of floor-based auction and electronic trading^[4].

4. 2024

   U.S. stock trades move to a one-business-day settlement cycle (T+1) on May 28, 2024^[6].

How are stock prices quoted: bid, ask and spread?#

At any moment, a stock has two prices, not one. The bid is the highest price a buyer will pay for a specified number of shares, and the ask is the lowest price at which a seller will sell^[7]. The difference between them is called the spread^[7]. The "price" you see in an app is often the last trade, which can differ from both.

Behind the quote sits a list of waiting orders, often called the order book. Buyers' limit orders stack up below the current price; sellers' limit orders stack up above it. When a new order arrives that is willing to trade at a waiting price, the exchange matches the two and a trade prints.

Buying at the ask and selling right away at the bid would cost the spread: $0.02 a share, or $2 on 100 shares in this example. In a busy, liquid stock the spread is usually small. In thinly traded stocks it can be much wider, which is one reason the order type you choose matters.

Where does your broker send your order?#

You cannot send an order to an exchange yourself; a broker does it for you. Broker-dealers charge a fee to handle trades between buyers and sellers of securities^[1]. The SEC explains that for a stock listed on an exchange, your broker may direct the order to that exchange, to another exchange, or to a market maker^[8] — a firm that stands ready to buy or sell a stock at publicly quoted prices^[9].

Some market makers pay brokers for routing orders to them; the SEC calls this payment for order flow^[8]. Whatever the route, your broker has a duty to seek the best execution reasonably available for customers' orders^[8]. Note what the SEC does not promise: its regulations do not require a trade to be executed within a set period of time^[8].

When can you trade, and what happens after the trade?#

Regular trading hours for stocks on U.S. exchanges run from 9:30 a.m. to 4:00 p.m. Eastern Time^[10]. Some brokers also offer extended-hours sessions before and after. The SEC warns that reduced trading interest in those sessions generally means wider spreads between bid and ask, and many brokers accept only limit orders then to protect investors from unexpectedly bad prices^[10].

Matching is not the end of a trade. Settlement is the official transfer of securities to the buyer's account and cash to the seller's account^[6]. Since May 28, 2024, most U.S. securities trades settle one business day after the trade date, a cycle called T+1; before that it was two business days^[6]. The SEC's own example: if you sell shares on Monday, the trade settles on Tuesday^[6].

Who protects investors in this system?#

In the U.S., the SEC registers national exchanges^[2] and requires public companies to file regular reports that anyone can read free on EDGAR^[11]. FINRA suggests EDGAR as a good place to start researching a company^[3]. These rules make prices and company information public; they do not make any stock safe. Prices still move on news, fear and hope — see what a stock is for the risks of ownership itself.

What mistakes do beginners make?#

1. Assuming the last price is the price you will get

   The number on the screen is usually the last trade. A market buy fills at the current ask, and a large order may fill at several prices.

2. Ignoring the spread

   Every round trip — buy, then sell — costs about the spread, on top of any commission. In thinly traded stocks this can be a noticeable share of the price.

3. Trading in extended hours without a limit

   Fewer participants mean wider spreads and bigger price jumps. Use limit orders if you trade outside regular hours at all.

4. Spending sale proceeds before settlement

   A sale is not final until it settles, one business day later in the U.S. Plan withdrawals around that delay.