When you submit an instruction, are you prioritising execution or setting a price condition? This example concerns ordinary share orders; broker rules and market conditions vary.
A quote is not a promise
A number on a screen is a snapshot. Between seeing it and an order reaching a venue, prices and available quantities can change. Understanding an order means understanding both what it asks for and what it cannot assure.
A market order asks to trade at the available market price. It generally prioritises execution, but it does not guarantee the price. A limit order adds a boundary: a buy limit can fill only at the specified price or lower; a sell limit only at that price or higher. A limit order can remain unfilled.
A small, invented order book
Imagine a fictional share. The displayed sellers are offering 5 shares at 50.00 and another 10 shares at 50.10. You want to understand what could happen to a 10-share buy instruction. These are simplified, invented quantities, not a real investment.
| Instruction | Illustrative outcome | What remains uncertain |
|---|---|---|
| Market buy, 10 shares | 5 at 50.00 and 5 at 50.10; average 50.05 before fees. | Quotes might change before execution; actual fills could differ. |
| Limit buy, 10 shares at 50.00 | Up to 5 might fill at 50.00, with the rest waiting. | Other orders may be ahead. Even the displayed quantity may not be available to you. |
The market example is a simple arithmetic illustration: (5 × 50.00 + 5 × 50.10) ÷ 10 = 50.05. It assumes those sellers are still available and omits commissions, taxes and venue-specific rules. The limit example does not promise even a partial fill.
Price control is a condition, not certainty
A limit says which prices are acceptable. It does not guarantee that anyone will trade with you, that sufficient quantity will be available, or that the order will have a favourable later outcome. Instructions about duration and partial fills also matter.
Before interpreting a fill, check the order status and execution report. A delayed screen is a poor reason to submit a second identical instruction: the first may already have executed. This note does not ask you to test the idea with real money.
Try it on paper
Change the fictional instruction to a 12-share market buy. Keep the displayed quantities unchanged. Calculate the possible average price in this simplified example, then write two assumptions that could prevent that result.
Read the worked explanation
Take the question with you
Instead of asking which order is “best”, ask what condition each instruction expresses, what can remain unresolved and how you would recognise an unintended outcome. You can explain that trade-off without placing a trade.
Primary sources & scope
- Investor.gov — Types of Orders: general definitions of market and limit instructions.
- Investor.gov — Executing an Order: routing and execution context.
- Investor.gov — Online Investing: checking order status before resubmitting.
Definitions are paraphrased. The example, calculations and exercise are original Courtyard learning material. Links do not imply regulatory approval or endorsement.