Market Order

A market order buys or sells immediately at whatever price is currently available, without naming one. It is the fastest way to fill, at the cost of not knowing the exact price.

In heavily traded large caps this is rarely a problem. Orders stack densely on both sides, so the fill lands almost exactly where you expected. It is the convenient choice when speed matters.

The danger is in thinly traded stocks. Where the gap between buyers' and sellers' prices is wide, a market order can execute far worse than anticipated — a cost known as slippage.

The first and last minutes of the session deserve the same caution: prices jump around, and market orders easily fill at odd levels. Unless you are in a hurry, a limit order is usually safer. For anyone buying a small amount monthly, a market order makes little difference: with modest sums in a broad index product, the spread is negligible.