A limit order is an order book instruction to buy or sell an asset at a predetermined price or a more favorable rate. Traders deploy limit orders when execution price certainty outweighs the necessity of immediate transaction settlement. A limit order specifies that a buy order executes only at or below the limit price, and a sell order executes only at or above the limit price.
Order Book Matching and Execution Mechanics
When submitted below the current ask price for a buy, or above the current bid price for a sell, a limit order does not execute immediately. Instead, the trading engine places the instruction onto the exchange order book, adding resting liquidity to the market. Matching engines prioritize these orders using standard price-time priority rules:
- Price Priority: Buy orders with higher bid prices and sell orders with lower ask prices execute before worse price levels.
- Time Priority: At any identical price level, orders that entered the order book first are filled before newer submissions.
- Partial Fills: If counterparty liquidity is insufficient to fill the entire quantity at the specified price, the order partially executes while the remainder rests on the book until filled or cancelled.
- Fee Classification: Resting limit orders generally qualify as liquidity maker orders, frequently incurring lower exchange fees than aggressive market taker orders.
Limit Orders Versus Stop-Loss Orders
Traders frequently evaluate limit orders alongside stop-loss orders. While a standard limit order immediately places a visible order onto the book at the target price, a stop-loss order remains hidden as an inactive conditional trigger. A stop-loss only submits an active market or limit order once a third-party trigger price is breached. Consequently, limit orders provide strict price bounds for entry and profit taking, whereas stop orders focus on risk mitigation by reacting to adverse market movement.