Stock Order Types: Market, Limit, Stop, Stop-Limit, and Trailing Stop Orders

A stock order type is the instruction that tells your broker how to trade: whether to fill immediately at whatever price is available, only at a price you set, or only after the price reaches a trigger. The choice is a trade-off between certainty of execution and certainty of price, and no order type gives you both.

In short: a market order gets filled fast but at an unknown price. A limit order names your worst acceptable price but may never fill. A stop order sits dormant until a trigger price is touched, then becomes a market order. A stop-limit order becomes a limit order instead. A trailing stop moves its trigger as the price moves in your favour. Each one solves a problem and creates another.

The order book, briefly

Every order type makes sense once you picture the order book: a list of standing offers to buy (bids) and to sell (asks) at different prices. The highest bid and lowest ask form the current quote. How that book sets prices is covered in how stock prices are set.

Here is a hypothetical book for Maple Widgets Inc. that we’ll use throughout:

Bids (buyers)	Shares	Asks (sellers)	Shares
$49.98	300	$50.02	200
$49.95	500	$50.05	400
$49.90	1,000	$50.10	800

The spread is $0.04 ($50.02 minus $49.98). The costs of that gap are covered in the bid-ask spread explained.

Market orders

A market order says: fill this now at the best available price.

If you send a market order to buy 100 shares of Maple Widgets, it fills at $50.02, the best ask, for $5,002.

If you send a market order to buy 500 shares, it walks the book: 200 at $50.02 ($10,004) and 300 at $50.05 ($15,015), for a total of $25,019, or an average of $50.038 per share. In practice, brokers route orders to venues where hidden liquidity or price improvement may change the result slightly, but the principle holds: a market order takes whatever is there.

Use it when: you care more about getting filled than about the last few cents, in a heavily traded stock, during regular hours.

What can go wrong: in a thinly traded stock, at the open, or during a sharp move, the price you get can be far from the price you saw. The SEC’s investor bulletin on order types makes the same point: the last traded price is not necessarily the price at which a market order will execute.

Limit orders

A limit order sets the maximum you will pay (on a buy) or the minimum you will accept (on a sell). It can fill at your limit or better, never worse.

A buy limit for 500 shares at $50.03 fills 200 shares at $50.02 immediately. The remaining 300 shares become a new bid at $50.03 on the book, waiting for a seller. If nobody sells at $50.03 or lower before the order expires, those 300 shares never fill.

A buy limit at $49.00 placed when the stock is at $50 does nothing unless the price falls to $49.00. A sell limit at $55.00 waits until someone will pay $55.

Use it when: price matters more than speed, in less liquid stocks, outside regular hours (many brokers accept only limit orders in pre-market and after-hours sessions), and whenever the spread is wide.

What can go wrong:

No fill. The stock runs away from you and the order never executes.
Partial fill. You get some shares and not others, and may pay commission on each portion at some firms.
Being filled for a bad reason. A buy limit far below the market fills precisely when bad news hits. A limit order says nothing about why the price arrived there.

Stop orders (stop-loss orders)

A stop order has a stop price that acts as a trigger. Until that price is reached, nothing happens. Once it is reached, the order becomes a market order.

A sell stop is placed below the current price, usually to limit a loss or protect a gain.
A buy stop is placed above the current price, for example to cover a short position if the price rises.

Say you own 100 shares bought at $50 and place a sell stop at $45. If the stock trades at $45, your order becomes a market order and sells at the next available bid.

The SEC’s bulletin on these orders is blunt: the stop price is a trigger, not a guaranteed execution price, and the fill can deviate significantly from the stop price in a fast-moving market. Firms also differ on what counts as “reaching” the stop price: some use the last trade, others use quotes.

The gap problem

Stop orders do not protect you overnight. If Maple Widgets closes at $48 and opens the next day at $38 after a bad earnings report, your $45 sell stop triggers at the open and sells at or near $38. The loss you expected to cap at about $500 on 100 shares (from $50) becomes roughly $1,200.

Stop-limit orders

A stop-limit order has two prices: a stop price that triggers it, and a limit price that sets the worst acceptable fill. When triggered, it becomes a limit order, not a market order.

Example: sell stop $45, limit $44. If the price touches $45, a sell limit at $44 goes live. It will sell at $44 or higher. In the gap scenario above, with the stock opening at $38, the order becomes a limit to sell at $44 that nobody will take. You keep the shares, and the loss continues.

That is the trade: a stop-limit guarantees a price floor but not an exit. FINRA describes it the same way: you regain price certainty and lose execution certainty.

Trailing stop orders

A trailing stop sets the stop price as a fixed dollar amount or percentage away from the market, and moves it only in your favour.

Using the SEC’s own style of example: you buy at $20 and set a sell trailing stop of $1. The stop starts at $19. If the stock rises to $24, the stop rises to $23. If the stock then falls, the stop stays at $23, and if the price reaches $23 the order triggers and becomes a market order (or a limit order, for a trailing stop-limit). As with any stop, the actual sale price may be below $23.

Price path	Highest price so far	Trailing stop ($1)
Buy at $20.00	$20.00	$19.00
Rises to $22.00	$22.00	$21.00
Rises to $24.00	$24.00	$23.00
Falls to $23.50	$24.00	$23.00 (unchanged)
Falls to $23.00	$24.00	Triggered

What can go wrong: a trail that is too tight gets triggered by normal day-to-day noise; a trail that is too wide gives back a large share of the gain. Volatile stocks move several percent in a day for no particular reason, which is why volatility is worth understanding before you pick a percentage.

Time in force

Every order also has a lifespan, called time in force:

Instruction	Meaning
Day	Expires at the end of the regular session if not filled. Generally does not carry into after-hours or the next day.
Good till cancelled (GTC)	Stays open until filled or cancelled, though most firms cap it (often at a set number of days).
Immediate or cancel (IOC)	Fill whatever you can immediately; cancel the rest.
Fill or kill (FOK)	Fill the whole order immediately or cancel all of it.
All or none (AON)	Fill the whole quantity or nothing, but the order may wait.
On open / on close	Execute in the opening or closing auction.

Whether an order is eligible for pre-market or after-hours sessions is a separate setting at most brokers. Those sessions carry their own risks, covered in market hours and after-hours trading.

What can go wrong across the board

Flash crashes

On May 6, 2010, US stock prices fell and recovered within minutes. The joint SEC and CFTC staff report found that more than 20,000 trades were executed at prices that were later broken because they were more than 60% away from reference prices, some at a penny a share. One cited example was Accenture, which traded at $0.01 against a placeholder “stub quote.” Market orders, including stop orders that converted to market orders, were among those filled at absurd prices. Rules adopted afterwards (single-stock circuit breakers that became the Limit Up-Limit Down mechanism, and a ban on stub quotes) make a repeat less likely, but sudden dislocations can still happen. The bigger picture is in stock market crashes in history.

Forgotten GTC orders

A good-till-cancelled limit to buy at a low price, placed months ago and forgotten, can fill on a day when the company has just announced bad news.

Orders on halted stocks

If trading is halted, your order waits. When trading resumes, the reopening price may be far from the pre-halt price, and market or stop orders fill at the new level.

Assuming the order is at the exchange

Stop and trailing stop orders are commonly held by the broker and released to the market only when triggered. Their behaviour (what triggers them, whether they work outside regular hours) depends on the firm’s rules, so read the firm’s order-type disclosures.

A simple decision guide

Liquid stock, regular hours, small order: a market order works, but a limit order at or slightly above the ask costs nothing extra and caps the price.
Wide spread, thin stock, or large order: a limit order.
Outside regular hours: limit orders only, and expect fewer fills.
Wanting to limit a loss: understand that a stop is an instruction to sell in a falling market, not a guarantee of the stop price; a stop-limit adds a price floor but may not sell at all.

The short version

Order types exist because you cannot have both a guaranteed fill and a guaranteed price. Market orders favour the fill, limit orders favour the price, and stops are conditional instructions that wake up when a trigger is hit. Most problems come from expecting an order to do something it never promised, such as a stop loss protecting you through an overnight gap.