Market order

A market order is an instruction to buy or sell a security immediately at the best price currently available. It prioritizes speed and certainty of execution over price.

How it works

A market buy order fills against the lowest available offers, and a market sell order fills against the highest available bids. For a liquid large-cap stock, a small market order usually fills at or very near the NBBO within milliseconds.

If the order is larger than the size at the best price, it "walks the book," filling at progressively worse prices until complete. The difference between the price you expected and the average price you received is called slippage.

Most brokers do not accept market orders outside regular trading hours, and many convert them to protected limit orders or reject them for thinly traded stocks.

Why it matters for traders

Market orders are the simplest way in or out, but they hand price control to whoever is on the other side. The risk is highest when:

• The bid-ask spread is wide, as in small caps or illiquid options.
• News just hit and quotes are moving fast.
• A stock is reopening from a halt, where the order joins an auction and can fill far from the last price.
• The market open is volatile, when quotes can be unstable for the first few minutes.

In those situations, a limit order sets a maximum purchase price or minimum sale price.

Example

Hypothetical Bluefin Robotics (ticker BFRB) shows offers of 500 shares at $3.10, 1,000 at $3.15 and 2,000 at $3.25. A market order to buy 2,500 shares fills 500 at $3.10, 1,000 at $3.15 and 1,000 at $3.25, for $7,950 in total, an average of $3.18. That is 8 cents, or about 2.6%, above the $3.10 offer the trader saw on screen.

FAQ

Is a market order or a limit order better?

Neither is always better. Market orders guarantee a fill but not the price; limit orders guarantee the price but not the fill. Liquidity and urgency decide which fits.

Can a market order fill at a terrible price?

Yes, especially in thin stocks, at the open, or when a stock reopens after a halt. That is why many brokers add price collars to market orders.