Order Types, and What Each One Guarantees
Every order type trades certainty of price against certainty of execution. There is no order that guarantees both, and most execution surprises come from expecting one to.
MadStockAlerts Research · Updated August 28, 2026
What to take away
- A market order guarantees a fill, not a price. A limit order guarantees a price, not a fill.
- A stop order is dormant until price trades through its trigger, then becomes a live order.
- A stop-market can fill far from its trigger in a price gap; a stop-limit can fail to fill at all.
- Time-in-force decides how long an unfilled order survives.
- A resting limit order supplies liquidity; a market order consumes it.
MAD Academy Training Video · 0:45
What Each Order Actually Guarantees
A market order guarantees a fill and not a price. A limit order guarantees a price and not a fill. Everything else follows from that.
This lesson is part of a Stock Alerts + Tools plan.
The trade-off underneath all of them
There are only two things an order can promise: that it will execute, and that it will execute at a particular price. No order type promises both, because promising both would require someone on the other side to be obliged to trade, and nobody is.
| Order | Guarantees | Does not guarantee |
|---|---|---|
| Market | Execution, essentially immediately | Any particular price |
| Limit | Price at least as good as stated | That it executes at all |
| Stop-market | Execution once triggered | The trigger price, or anything near it |
| Stop-limit | Price once triggered | That it triggers into a fill |
| Market-on-close | Execution in the closing auction | The auction price, which is unknown beforehand |
Every complaint about an execution reduces to expecting the column on the right. Understanding which guarantee was actually bought removes almost all of that surprise in advance.
Market orders
A market order takes whatever the order book offers, walking up or down through resting orders until it is filled. In a liquid large-cap during the regular session the result is usually within a cent of the screen, because there is depth at every price and the order never has to reach far.
In a thin stock, in the first minute of the day, or in extended hours, it can be dramatically worse, because the book is shallow and the order simply consumes it. The same instruction produces a routine fill in one security and a painful one in another, and nothing about the order changed.
The classic surprise
A market order placed while the market is closed executes into the opening auction or the first prints of the session, not at the price displayed when it was entered. Overnight news can put that price a long way from expectation, and the order carries no protection whatsoever against it.
Limit orders
A limit order states the worst price acceptable. A buy limit at 42.00 will fill at 42.00 or lower and never higher. If price never reaches it, nothing happens, which is the cost of the guarantee.
Because a resting limit order joins the queue at its price, it is also the way liquidity is supplied rather than consumed. That is the structural difference between a limit order and a market order, and it is why some venues rebate the first and charge for the second: one of them made the market better and the other used it up.
A limit order also leaks information. A large resting order is visible to everyone watching the book, and its presence tells other participants where a buyer is. Traders working size therefore break orders into pieces or use order types that hide the remainder, which is a whole discipline of its own.
Stop orders
A stop order sits inert until price trades through a trigger level, at which point it converts into either a market order or a limit order depending on which variant was chosen. It is not visible in the order book beforehand and provides no liquidity while dormant.
- 1Stop-marketConverts to a market order on trigger. It will get out, but in a price gap or a fast move the fill can be far below the trigger.
- 2Stop-limitConverts to a limit order on trigger. It protects against a terrible fill and, in exactly the same scenario, may not fill at all.
- 3Trailing stopMoves its trigger as price advances, keeping a fixed distance or percentage behind the best level reached, and never moving back down.
Both stop variants fail in the same event and in opposite directions. A stock that gaps down twenty percent overnight fills a stop-market at the open, well below the trigger, and leaves a stop-limit unfilled with the position intact. Neither behaviour is a malfunction; they are the two available answers to an impossible question.
Because a stop is invisible until it fires, a cluster of them just below an obvious low is a pool of latent selling that nobody can see. When price reaches that level, the stops convert to market orders at once and the resulting supply can carry price further than the initial move justified.
Time in force
- Day: expires at the close of the regular session if unfilled.
- Good-till-cancelled: survives across sessions, usually with a broker-imposed maximum of 30 to 180 days.
- Immediate-or-cancel: fills whatever is available now and cancels the remainder.
- Fill-or-kill: fills the entire quantity immediately or cancels entirely.
- Market-on-close and limit-on-close: participate in the closing auction, with a cut-off well before the bell.
- Extended-hours flags: many brokers require an explicit flag before an order is eligible outside the regular session, and most reject market orders there.
A good-till-cancelled order is worth a specific caution: it survives corporate actions that change the price. A limit order at $50 left resting through a two-for-one stock split is suddenly a long way from the market, and brokers differ in whether they adjust it.