Glossary
Market order
An order to buy or sell immediately at the best available price; it guarantees execution but not the price.
On this page
A market order tells your broker to buy or sell right away at the best price currently available. It is the simplest order type and, in a liquid stock during regular hours, usually fills within a fraction of a second. What it does not promise is the price: you get whatever the market offers at the moment the order arrives, which can differ from the quote you saw.
How it fills
A buy market order executes against the lowest asks available; a sell order executes against the highest bids. If the order is larger than the size offered at the best price, the remainder fills at the next prices, a process often called walking the book.
When it causes trouble
The gap between the expected and actual price is slippage, and it grows when spreads are wide or prices are moving fast: at the opening bell, around news, in small or illiquid stocks, and during trading pauses. A market order entered while a stock is halted will execute when trading resumes, possibly far from the last price. Many brokers do not accept market orders in pre-market and after-hours sessions for these reasons.
For large orders, or any time price matters more than speed, traders often use a limit order instead, or a marketable limit order set a little through the current quote.