A buy limit order only executes when the market price of the stock is at or below the order's limit price. So, generally speaking, if you place a buy limit order with a price that's above the market price, the order will execute (perhaps at a better price). However, this won't be so if the market price gaps. Say, you place a buy limit order with a price that's above Monday's closing market price for a stock. You're planning to buy the stock the following day at no more than your limit price as the market trends upward. At the opening on Tuesday morning, the stock price unexpectedly gaps up sharply, completely bypassing your limit price. In such a case, your order will fail to fill.