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Order Types Explained: Stop Loss, Trailing Stop, Limit and Spread
Aman Anand
Short answer: A market order buys or sells right away at the best available price, a limit order trades only at your price or better, and a stop loss is a stop order that turns into a market order once a trigger price is hit. A trailing stop is a stop whose trigger follows the price by a set percentage or dollar amount. The bid ask spread, the gap between the highest bid and the lowest ask, is a cost you pay every time you cross it with a market order.
Last updated October 2026. Definitions follow the SEC's investor education pages on order types and stop, stop-limit and trailing stop orders, as of October 2026. Brokers set their own rules for some order types, so check yours. This guide is educational and is not financial advice.
What is the bid ask spread?
Every quote has two prices. The bid is the highest price a buyer is willing to pay right now. The ask (or offer) is the lowest price a seller will accept. The SEC's Investor.gov glossary calls the difference between them the spread, and notes that the bid is almost always lower than the ask.
Why is the bid-ask spread a cost?
When you buy with a market order, you usually pay the ask. When you sell with a market order, you usually receive the bid. If you bought and sold instantly, you would lose the spread even though the "price" of the stock never moved. Commission-free trading does not remove this cost.
Worked example: the cost of crossing the spread
Say a stock is quoted at a bid of $50.00 and an ask of $50.05. The spread is $0.05.
You buy 200 shares with a market order and pay about $50.05, or $10,010.
If you sold right away at the $50.00 bid, you would get $10,000.
The round trip cost you $10, roughly 0.1% of the position, before any price movement or fees.
That looks small, but a strategy that trades several times a day pays it again and again.
Why do spreads vary?
Spreads depend mostly on liquidity, meaning how many buyers and sellers are active. Large, heavily traded stocks and ETFs tend to have very tight spreads. Small, thinly traded stocks can have wide ones. Spreads also widen when volatility jumps, around the open, and outside regular hours. The SEC's bulletin on after-hours trading warns that lower trading interest in extended hours generally means wider spreads between bid and ask.
What is a market order?
A market order is an order to buy or sell immediately at the best available price. According to Investor.gov, it guarantees execution but does not guarantee the price.
In liquid stocks during regular hours, the fill is usually close to the quote. In fast or thin markets, the price can move first. The gap between the expected and actual price is called slippage.
Best use: getting in or out quickly in liquid markets, when certainty of execution matters more than a few cents.
What is a limit order? Buy limit vs sell limit
A limit order is an order to buy or sell at a specific price or better. It controls price but does not guarantee execution: if the market never reaches your price, nothing happens.
Buy limit: executes only at your limit price or lower. Traders place it below the current price to buy a pullback.
Sell limit: executes only at your limit price or higher. Traders place it above the current price to take profit at a target.
Worked example: a sell limit order
You own 100 shares bought at $40. The stock trades at $43, and your plan is to take profit at $45. You place a sell limit at $45.
If the stock reaches $45 and buyers are there, your order can fill at $45 or higher.
If it peaks at $44.90 and falls back, you never sell. That is the trade-off.
A sell limit set below the bid, say $42 with the bid at $43, usually fills right away near the bid.
A buy limit placed at the bid also avoids paying the spread, though it may never fill.
What is a stop loss order?
A stop order is an order to buy or sell once the price reaches a specified level, called the stop price. When the stop price is reached, it becomes a market order. A stop loss is simply a sell stop placed below the current price on a stock you own (or a buy stop above the price on a short), meant to cap the loss on a trade.
Example: you buy at $40 and place a sell stop at $36. If the stock trades at $36, your order becomes a market order and sells at the next available price, which may be lower.
The SEC states plainly that the stop price is not a guaranteed execution price, and that a short, intraday move can trigger a stop and leave you with a price well below where the stock closes that day.
What is a stop-limit order?
A stop-limit order combines both ideas. When the stop price is reached, it becomes a limit order instead of a market order. You set two prices: the stop (the trigger) and the limit (the worst price you will accept).
Example: a sell stop-limit with a stop at $36 and a limit at $35.50. If the stock falls to $36, the order becomes a sell limit at $35.50 and fills only at $35.50 or better. If the stock drops straight through $35.50, the order may not fill, and you still hold a falling position.
What is a trailing stop?
A trailing stop is a stop or stop-limit order whose stop price is not fixed. Instead, it is set a defined percentage or dollar amount away from the market price. As the price moves in your favor, the stop moves with it. When the price moves against you, the stop stays where it is.
Worked example: dollar vs percent trailing stop
You buy at $20. The stock rises to $24, then falls.
$1 trailing stop: the stop follows $1 below the highest price. At a $24 peak, the stop sits at $23. If the stock falls to $23, the order becomes a market order and sells near $23, though the fill can be lower.
5% trailing stop: the stop follows 5% below the highest price. At a $24 peak, the stop sits at $22.80. The dollar distance grows as the price rises, which suits stocks that trade at very different price levels.
The catch: a tight trail on a volatile stock gets hit by normal noise. Size the trail to how much the stock usually moves.
Do stops guarantee your price? What about gaps?
No. A stop triggers at the stop price, but fills at the next available price.
Gaps: if a stock closes at $40 and opens at $33 after bad news, a sell stop at $36 triggers at the open and fills near $33, not $36. A stop-limit with a $35.50 limit would not fill at all.
Fast markets: FINRA's Regulatory Notice 16-19 warns that once triggered, a stop order may execute at a price significantly different from the stop price when the market is moving rapidly.
A stop is not a hard cap on loss. Position size is the real control. See our guide to position sizing.
What do day and GTC mean? (time in force)
Day order: good only for the trading day it is entered. If it is not filled, it is canceled at the close and does not carry over to the extended-hours session or the next day.
Good-til-canceled (GTC): stays open until it fills or you cancel it. Investor.gov notes that how long a broker lets a GTC order stay open varies by firm, so ask yours. Many brokers cancel GTC orders automatically after a set period.
A forgotten GTC order can fill weeks later in a very different market, so review open orders regularly.
How do orders behave in extended hours?
Pre-market and after-hours sessions have fewer participants. According to the SEC, that means less liquidity, wider spreads, bigger price swings, and many brokers accepting only limit orders. Brokers also differ on whether stops can trigger outside the regular session. Our stock market hours guide lists the sessions.
Order types compared
Order type | Guarantees execution? | Guarantees price? | Best use |
|---|---|---|---|
Market | Yes, if there are buyers or sellers | No | Fast entry or exit in liquid markets |
Limit (buy or sell) | No | Yes, your price or better | Entries at a planned price, profit targets, thin markets |
Stop (stop loss) | Yes, once triggered | No, can fill well past the stop | Exiting a losing trade when getting out matters most |
Stop-limit | No | Yes, limit price or better | Exits where a bad fill is worse than no fill |
Trailing stop | Yes, once triggered (if stop-market) | No | Protecting open gains in a trending position |
How do order types affect a backtest?
Many backtests assume every order fills at the exact price on the chart. Real orders do not work that way, and the gap is one of the main reasons backtests do not match live results.
Market orders and stops pay the spread and slippage. A realistic test subtracts a cost on every fill. Stops in a gap should fill at the open, not at the stop price.
Limit orders may not fill. If price only touches your limit, a real order may sit behind others in the queue. Conservative tests count a fill only when price trades through the limit.
Bars hide the order of events. If one daily bar touches both your stop and your target, the test cannot know which came first. Assume the worse one.
For a checklist, see our guide to effective backtesting.
Where Nvestiq fits
Nvestiq lets you describe a strategy in plain English, including entries, stop losses, trailing stops and profit targets, and a deterministic compiler turns that description into exact logic rather than freeform code written by a language model. The backtest report shows what the strategy made, what it cost to hold, and whether to believe it, and it flags when buy and hold beat the strategy. You can then paper trade it or connect Interactive Brokers, or export it to Python, Pine Script or JSON. Nvestiq is in early access, with public launch following final legal review.
Frequently Asked Questions
What is the difference between a stop loss and a stop-limit order?
A stop loss becomes a market order when triggered: it should get you out, at no guaranteed price. A stop-limit becomes a limit order: it controls price but may not fill.
Is a trailing stop better than a regular stop loss?
Neither is better in general. A fixed stop limits the loss from your entry. A trailing stop moves up as the trade works, protecting part of the gain.
When should I use a sell limit order?
Use a sell limit when you want to sell at a specific price or higher, usually to take profit at a target above the current price. It will not fill if the price never gets there.
What is a good bid ask spread?
There is no single number. Compare it to the price and to how often you trade. A few cents matters little on a stock you hold for months, and a lot when paid many times a day.
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Risk Disclosure
Trading involves substantial risk of loss. Past performance and backtested results do not guarantee future results. Nvestiq provides technology tools, not financial advice.