What it means
A limit order sets a price boundary for a stock trade. A buy limit order can execute at its limit price or lower; a sell limit order can execute at its limit price or higher. It may fill immediately, later, partially, or not at all. A limit price controls the worst permitted execution price, not whether a trade will happen.
An order can be marketable when submitted: for example, a buy limit at or above the current best ask may match an available seller. The quoted price and available shares can change before the order reaches the market, so even a marketable limit order is not guaranteed a complete fill. If the limit is not marketable, the order may rest and wait for a matching counterparty, subject to the broker's handling and its time-in-force instruction.
How it is calculated
The limit price is chosen by the person placing the order; it is not calculated from market data. Its price boundary and the value of any executed shares can be expressed as:
- Buy:
execution price per share <= buy limit price per share - Sell:
execution price per share >= sell limit price per share - Executed share value:
filled shares × execution price per share
Here, execution price per share is the actual fill price in US$ per share, buy limit price per share is the highest permitted buy price in US$ per share, sell limit price per share is the lowest permitted sell price in US$ per share, and filled shares is the number actually traded, which may be less than the quantity requested. Executed share value is in US$ and excludes commissions or other charges. The limit constrains each fill's price, not the total cost after fees.
Worked example
Suppose, hypothetically, an investor submits a limit order to buy 100 shares at US$50.00 per share:
- The buy limit sets a maximum execution price of US$50.00 per share. If all 100 shares fill at that price, executed share value is
100 × US$50.00 = US$5,000, before charges. - If 40 shares instead fill at US$49.90, their executed share value is
40 × US$49.90 = US$1,996. The unfilled 60 shares may remain open or be canceled, depending on the order's time-in-force and broker handling. - If the lowest available ask stays at US$50.10, no shares execute at that ask because it exceeds the US$50.00 buy limit. A later change in available prices could still allow a fill while the order remains active.
For a hypothetical sell limit of US$50.00, the direction reverses: a fill at US$50.10 is permitted, but one at US$49.90 is not.
Why it matters before you trade
A limit order trades certainty about the permitted share price for uncertainty about execution. A market order instead seeks prompt execution without setting a maximum buy price or minimum sell price. Neither order type guarantees a particular total transaction cost.
Before placing an order, distinguish the quoted bid and ask from prices at which your entire quantity might execute. Available quantity at a quoted price can be smaller than your order. Liquidity, spread, market impact, tick size, trading hours, and time-in-force can all affect whether and when a limit order fills. A missed or partial fill also matters when several stocks are intended to trade together: the executed basket may differ from the planned basket.
How PreTrAIde uses it
PreTrAIde performs pre-trade analysis of a stock basket before any order is placed. A user enters each stock's buy or sell side, quantity, and execution conditions. Its analysis returns a GO, NO-GO, or MODIFY verdict for the basket and each line, with a risk assessment, suggested execution strategy, and plain-language reasoning. Its quantitative layer estimates spread, participation in daily volume, and market impact—factors relevant when checking execution conditions. The product facts do not specify a dedicated limit-order fill-probability calculation.
PreTrAIde is decision-support software, not a broker. It does not receive, transmit, or execute limit orders; users place any trades themselves through their own broker.
Common mistakes
- Treating the limit as a fill promise. A qualifying counterparty and sufficient available shares are still needed.
- Confusing a buy and sell limit. The buy limit is a ceiling; the sell limit is a floor.
- Assuming a full fill. Part of an order can execute while the rest remains unfilled.
- Ignoring time-in-force. It governs how long an unfilled order can remain active, subject to broker and market rules.
- Equating the limit with total cost. Commissions or other charges can change the amount paid or received.