Key Takeaways
Quick answer
A market order is an instruction to buy or sell straight away at the best price currently available. It is the order type most likely to fill, but the SEC notes the execution price is not guaranteed, particularly for large orders or in fast-moving markets.
- A market order trades immediately at the best price available.
- The SEC says its execution price is not guaranteed, especially for larger orders.
- Buying at the ask and selling at the bid means every market round trip pays the spread.
How does a market order work?
The SEC’s definition is short: “A market order is an order to buy or sell a stock at the best available price.” FINRA adds that it generally executes at or near the current bid or ask. In practice a market buy pays the ask and a market sell receives the bid, so you cross the spread immediately.
Why might a market order fill at a different price?
Each price level in an order book holds only so many units. If your order is larger than the best level, the rest fills at the next prices up. The SEC states that “the price at which a market order will be executed is not guaranteed.”
| Ask level | Units filled | Cost |
|---|---|---|
| $100.00 | 1 | $100.00 |
| $100.40 | 1 | $100.40 |
| $101.00 | 1 | $101.00 |
Illustrative: buying 3 units costs $301.40 in total, an average of $301.40 ÷ 3 = $100.47, not the $100.00 shown at the top of the book. That gap is slippage.
When would you choose a market order over a limit order?
The choice is speed against price control. A market order gets you in or out now and accepts the going rate. A limit order names the worst price you will accept and may wait, or never fill. Our guide to order types compares them in detail.
What are the risks of using market orders?
- Thin markets. With little liquidity, a single order can walk far up or down the book.
- Fast moves. FINRA cautions that when prices are moving quickly, the fill may differ from the quote on your screen.
- Hidden triggers. A stop-loss turns into a market order when it fires, so it carries the same price risk.
These descriptions come from US stock regulators. Crypto platforms write their own order rules, so check them before you trade.
Frequently asked questions
Is a market order filled instantly?
Usually within moments when the market is active, because it accepts whatever price is available. Speed is its main advantage; the exact price is the trade-off.
Do I pay the spread with a market order?
Yes. Buying at the ask and selling at the bid means a round trip costs at least the spread, before any platform fee.
Article Sources
3 sources
Blockhorizon checks every figure, date and quotation against primary sources: regulators, statistics bodies and original technical documents. Read our editorial policy.
- SEC Investor.gov, Investor Bulletin: Understanding Order Types — investor.gov (accessed 2026-10-02)
- FINRA, Order Types — finra.org (accessed 2026-10-02)
- SEC Investor.gov, Bid Price/Ask Price (glossary) — investor.gov (accessed 2026-10-02)