The short answer
A market order seeks the best available price, but its execution price is not guaranteed and can differ from the last trade.[1] A limit order sets a maximum purchase price or minimum sale price, but may never execute.[1][3] The choice is between accepting execution-price uncertainty and accepting the possibility of no trade.[1]
The screen price is not a promise
Investor.gov explicitly warns that the last-traded price is not necessarily the price a market order receives.[1] FINRA identifies delayed quotes, execution time and fast market movements as reasons a displayed price can differ from the eventual purchase price.[3] Even a real-time quote does not lock in the available liquidity when your order arrives.[1]
Before submitting an order, distinguish the displayed last trade from the current bid and ask, and check the timestamp and quantity. Quotes apply to a particular number of shares, not an unlimited quantity at that price.[2] Treat the screen as information to inspect, not a confirmed transaction.
A market order prioritizes trading, not a fixed price
A market order instructs a broker to buy or sell at the best available price and generally executes immediately; the price is not guaranteed.[1] FINRA says market orders generally execute at or near current bid or ask prices during normal trading hours.[3] “Generally” is important: the SEC explains that execution takes time and is not required within a fixed period.[2]
Other orders can consume available shares first, leaving a later market order to execute at a different price.[1] A larger order can also receive several execution prices when insufficient shares are available at one price.[1] Do not interpret a market order as an instruction to trade at the last recorded sale.
A hypothetical fill with two prices
Assume a fictitious stock last traded at $50.00. Suppose your market purchase of 100 shares receives 40 shares at $50.10 and 60 at $50.20. These fills are stipulated for teaching, with no fees, no other fills and no claim about a live order book.
The share cost is 40 × $50.10 + 60 × $50.20 = $5,016; the quantity-weighted average execution price is $50.16. Compared with 100 × the hypothetical last price, the difference is $16, or 0.32%. This is arithmetic under the assumptions, not a forecast or evidence of broker misconduct. Multiple-price fills are a possibility described by the SEC.[1]
A limit is a boundary, not an exact-price demand
A buy limit can execute only at its limit price or lower; a sell limit only at its limit price or higher.[1][3] The limit therefore permits a better price rather than requiring every fill to equal the number entered.[1] Unlike a market order, it can remain unexecuted.[1]
In a separate hypothetical scenario, place a 100-share buy limit at $50.10 and assume only 40 shares fill at $50.10, with no additional shares available at or below the limit. Those fills cost $2,004, and 60 shares remain unfilled. Paying $50.20 for the remainder would violate this buy-price boundary.[1] This example assumes partial fills are allowed and does not promise queue priority.
Choose the order lifetime as well as its price
The SEC describes day orders as generally canceling at the end of regular trading hours if unexecuted, without carrying into extended hours or the next day.[1] Good-til-canceled orders remain active until fully executed or canceled, but brokerage firms can impose different time limits.[1] Check the broker’s actual expiration policy.
Immediate-or-cancel instructions cancel any portion that cannot execute immediately; fill-or-kill instructions require immediate execution of the whole order or cancellation.[1] All-or-none instructions require the entire quantity but, unlike fill-or-kill, can remain active rather than execute immediately.[1] Ask which combinations your broker supports before assuming a price limit also controls timing or partial fills.
An overnight order does not preserve yesterday’s price
FINRA warns that an order placed outside normal trading hours may encounter a significantly different price when the market next opens because of news or other factors.[3] Order types and instructions available to customers vary by brokerage firm.[1] Confirm the eligible session instead of assuming an order entered at night trades immediately.
A stop order is not a substitute for a price limit: after its stop price is reached, it becomes a market order, whose execution can differ substantially from the trigger.[1] A stop-limit instead becomes a limit order, retaining the risk of no execution.[1] Keep trigger prices separate from guaranteed price boundaries.
Audit the execution, not just the chart
The broker has a duty to seek the best execution reasonably available; price improvement is an opportunity, not a guarantee.[2] That duty is not a promise to reproduce the last trade shown on your screen.[1][2] FINRA also cautions that no order type completely removes market and investment risk.[3]
For a practical review, save the order type, side, quantity, limit, session and duration. Compare the execution report’s individual quantities and prices with the submitted instructions, then calculate the weighted average separately from any fees. If something conflicts, ask the broker for its execution explanation. Choose the uncertainty you can accept before pressing submit.
Sources & scope
Links support definitions and methodology. Worked examples are hypothetical, not quotes; the review date is not the observation date of a market value.
- SEC Investor.gov — Understanding Order Types, Investor Bulletin (updated) ↗
Source date: 2026-08-18 · Verified: 2026-09-20
- SEC Investor.gov — Executing an Order (publication date not stated) ↗
Source date: Not stated in the retrieved body · Verified: 2026-09-20
- FINRA — Order Types (publication date not stated) ↗
Source date: Not stated in the retrieved body · Verified: 2026-09-20