The quote on screen is not a promise
When you place a trade, you are sending instructions through a broker to a market. The price you last saw may change before the order reaches the trading venue. This is why the choice between a market order and a limit order is more than a button in an app: each gives up something different.
The U.S. Securities and Exchange Commission’s Investor.gov describes a market order as an order to buy or sell at the best available price. It is generally executed quickly, but the exact execution price is not guaranteed. A limit order sets a maximum purchase price or minimum sale price, but may not execute at all.
Market order: favour execution
Imagine an ETF’s displayed last trade is US$100. You submit a market buy. If the available sellers are now offering at US$100.20, the order may fill there instead. In a thin or fast-moving market, different portions of an order can fill at different prices.
The last traded price is historical: it tells you where a previous transaction happened, not what a seller will accept now. Before submitting a market order, look at the live bid and ask, the size available, and whether the instrument trades actively. The broker may route the order to a venue according to its own execution process, so read the broker’s order and execution terms too.
Limit order: set your boundary
A buy limit at US$100 means you will pay US$100 or less per share. A sell limit at US$100 means you will accept US$100 or more. The limit is a price condition, not a prediction about where the market should trade.
Suppose you place the buy limit at US$100 while sellers are asking US$100.20. Your order may wait. If the price never reaches US$100 while the order is active, you may own no shares at all. If only a small quantity is available at your limit, the order could fill partially, depending on the venue and the order instructions supported by your broker.
That is the trade-off in one line: a market order prioritises getting a fill but cannot guarantee the price; a limit order controls the price boundary but cannot guarantee a fill.
What about stop orders?
A stop order adds a trigger. When its stop price is reached, it generally becomes a market order, so the eventual execution price can differ from the stop price. A stop-limit order instead becomes a limit order after the trigger, which sets a price boundary but can leave the order unfilled if the market moves past it.
These labels and mechanics are general descriptions. Order types, durations, trigger rules and cancellation options vary across brokerages and trading venues. Check the exact terms shown by your broker before using an order type you have not used before.
A simple pre-trade routine
Before confirming an order, pause and check:
- Am I buying or selling, and is the ticker and exchange correct?
- What currency is the order in, and do I have enough available balance?
- Is the displayed figure a last trade, bid, ask, or indicative price?
- Do I care more about execution or about limiting the price?
- How long will the order remain active, and what happens if it is only partly filled?
There is no universally best order type. Matching the instruction to the task is the point. For a long-term investor, understanding a basic limit order and its chance of not filling is usually more useful than adding complex triggers to a simple purchase.
Sources
- U.S. SEC Investor.gov: Understanding Order Types — updated 18 Aug 2026; verified 5 Oct 2026.