How a market order works
The matching engine fills a market buy from the lowest-priced sell orders upwards, and a market sell from the highest bids downwards. If the best price level does not hold enough quantity, the order moves to the next level, and the next, so the average fill price drifts away from the quote. The drift is slippage.
A market order never rests in the book, so the order is always a taker and pays the taker fee. On many platforms a market buy can be entered as an amount to spend instead of a quantity to receive.
How platforms protect market orders
An unprotected market order in a thin book can fill at absurd prices. Exchanges therefore limit how far one can go:
- A price band: the order stops filling beyond a set distance from a reference price
- Conversion to a limit order at a protective price
- A maximum order size per market
- A preview of the estimated price and fee before confirmation
- Rejection when the book is empty or trading is halted
Who uses market orders
Retail apps lean on them, often behind a plain buy button, because certainty of execution is what a first-time buyer expects. Brokers and on-ramps that quote a fixed price for a few seconds offer the same certainty without exposing the customer to the book.
Market order or limit order?
- Limit order
- Sets the worst acceptable price and waits if the market is not there. The price is certain and the trade is not.
- Stop order
- Sleeps until a trigger price is reached, then usually becomes a market order.
Where a market order shows up in a platform
Modules that do the work
- Matching engineA low-latency order book for spot markets, with market makers and outside liquidity.
- Market dataLive and historical prices for crypto, stocks and FX, from the data vendors you choose.
- LedgerThe double-entry book of record behind every balance, fee and transfer.