What a Stop-Loss Order Does and Does Not Protect

A stop-loss order is an instruction to sell (or, for a short position, buy) once a price is reached. It caps how long a losing position stays open, not the price at which it closes: the stop price is a trigger, and the fill depends on the order type and on the market at that moment.

Key takeaways

A plain stop order turns into a market order when the stop price is reached, so the fill can be far from the stop price; a stop-limit order caps the fill price but may not fill at all.
A trailing stop moves only in the investor's favor and stays fixed when the price turns against the position.
Gaps at the open, extended-hours sessions and short-lived price spikes are three situations in which a stop can behave differently from what the investor pictured.
FINRA calls stop orders a possibly useful tool for investors who cannot monitor prices, and regulators warn they can sell into a brief drop that later reverses.

Three kinds of stop order

The SEC's Office of Investor Education and Assistance describes three variants in its Investor Bulletin on stop, stop-limit and trailing stop orders (July 13, 2017, updated August 18, 2026), which also says these orders may not be available at every brokerage firm.

Order	What happens at the stop price	Main trade-off
Stop (stop-loss, stop-market)	Becomes a market order	Fills quickly, but the price can deviate significantly from the stop price
Stop-limit	Becomes a limit order at the chosen limit price or better	Controls the price, but may not execute if the market moves away from the limit
Trailing stop	The stop price follows the market by a set percentage or dollar amount, then acts as a stop or stop-limit order	Adjusts as the price rises, but short-term swings can trigger it

A sell stop sits below the current price. In a stop-limit order the stop and limit prices need not match: the bulletin's example pairs a $3.00 stop with a $2.50 limit.

What actually triggers a stop

The bulletin says firms apply different standards for deciding that a stop price has been reached: some use only last-sale prices, others use quotation prices. FINRA's Rule 5350 says a firm may, but is not obligated to, accept stop orders, and defines a stop order as one that becomes a market order when a transaction occurs at or through the stop price. It allows firms to offer an order that activates on a quotation instead, but such an order may not be labeled a "stop order" and the firm must describe its triggering event to the customer before the order is placed.

An SEC staff memorandum to the Equity Market Structure Advisory Committee (January 26, 2016) adds that, at some brokers, a stop may be triggered only by a round-lot transaction at the stop price. The same stop price can therefore trigger at different moments at different firms.

It also notes that stops are usually held by the brokerage firm, which sends the order to the market once triggered, rather than resting on an exchange's book. FINRA's investor page on stop orders in volatile markets says the risks of the order type have led certain exchanges to stop accepting it. One example is the New York Stock Exchange, which filed in December 2015 to remove stop orders and good-til-canceled orders from its rules, saying elected stop orders "can exacerbate market volatility."

When a stop is not working

Extended hours

FINRA's extended-hours guidance (July 31, 2024) says firms may accept only limit orders outside regular hours, may cancel or carry over unexecuted orders differently, and may not offer extended-hours trading at all. It also says the National Best Bid and Offer is published only in regular hours, so the best-price requirement does not apply then. No regulator page says how a particular firm treats stops outside regular hours; that answer has to come from the firm's order terms.

Gaps at the open

News after the close can put the first regular-hours price well below the stop. The SEC staff memorandum states that the Limit Up-Limit Down mechanism does not constrain price movements between one day's close and the next day's open. A stop below the previous close is therefore not a floor. It becomes a market order when the price reaches or crosses it, usually at the open.

Halts and pauses

During regular hours, Investor.gov's circuit breaker glossary says a stock that hits its Limit Up-Limit Down price band and stays there for 15 seconds pauses for five minutes. The mechanism applies only from 9:30 a.m. to 4:00 p.m. Eastern.

Two documented sell-offs

May 6, 2010

The September 30, 2010 joint report by CFTC and SEC staff on May 6, 2010 mentions stop-loss orders in several places. Its executive summary says that after 2:45 p.m., even as index products recovered, sell orders in some stocks and ETFs, including

"many retail stop-loss orders, triggered by declines in prices of those securities"

met reduced buying interest, which led to further price declines in those securities. The report also says some market orders executed as low as one penny or as high as $100,000 against stub quotes: quotes set far from the market so that a market maker technically meets its obligation to quote both sides.

A later section says many retail orders that began as stop-loss or market orders were converted to limit orders by internalizers (firms that fill retail orders themselves) before routing to the exchanges. When a limit could not fill as prices kept falling, the internalizer lowered it and resubmitted, following the price down to unrealistically low bids. After the close, the exchanges and FINRA cancelled the more than 20,000 trades executed 60% or more away from their 2:40 p.m. prices. Fills less far away were not covered. The report does not say how many executions began as stop orders.

August 24, 2015

The SEC staff research note on equity market volatility on August 24, 2015 (December 2015) shows the opening gap. The SPDR S&P 500 ETF Trust opened 5.2% below the prior close, fell to a daily low 7.8% below it by 9:35, passed its opening price by 9:40, and closed down 4.2%. Single stocks swung further: in the note's table, JPMorgan Chase traded 21.3% below its prior close at its low but closed down 5.3%. The note never mentions stop orders, but the SEC staff memorandum uses that morning to illustrate the price risk that market orders share with stop orders that convert to them: in the first 15 minutes, more than 20% of S&P 500 companies traded 10% or more below the previous close.

Three worked examples

All prices below are hypothetical, chosen for round arithmetic, and ignore commissions and fees.

Example 1: an 8% trailing stop

A holder buys at $100 and sets a sell trailing stop 8% below the highest price reached. The stop equals 92% of the peak.

Price	Highest so far	Stop (92% of highest)	Result
$100	$100	$92.00	Holding
$112	$112	$103.04	Holding
$120	$120	$110.40	Holding
$115	$120	$110.40	Holding, stop does not fall
$108	$120	$110.40	Triggered when price crossed $110.40

If the price moves through $110.40 during the session, a stop-market order sells near $110.40 (the bulletin warns the fill can differ): $9.60, or 8%, below the $120 peak, 10.4% above the purchase and $2.40 above the $108 where the series ended. If the price instead jumped from $115 to $108 overnight, the sale would be near $108, 10% below the peak.

Example 2: a gap past a $95 stop

A holder owns 200 shares bought at $100 and places a stop at $95, a planned loss of $5 per share or $1,000. Overnight news pushes the next open to $88.

Stop (market): sells near $88 at the open. The loss is $12 per share, or $2,400, against the $1,000 planned.
Stop-limit with a $94 limit: becomes active but can only fill at $94 or better. If the price slides from $88 to $80, it never fills: the 200 shares are worth $16,000, an unrealized loss of $4,000, or $1,600 more than the stop-market sale.

Had the price recovered to $94 within the session, the stop-limit would have filled there while the stop-market had already sold at $88. The stop-market fails on price, the stop-limit on execution.

Example 3: a whipsaw

A holder buys 100 shares at $60 and sets a stop 5% below, at $57.00. During the session the price dips to $56.50 on a short-lived spike and closes at $61.

Stopped out at $57.00: 100 × ($57.00 − $60.00) = −$300, a 5% loss. If the fill came at the day's low of $56.50, the loss would be $350.
Held through the day: 100 × ($61.00 − $60.00) = +$100, a gain of 1.7%.

Being stopped out cost $400 relative to holding, 6.7% of the purchase price, on a stock that closed above the entry. The Investor.gov bulletin and FINRA Regulatory Notice 16-19 (May 26, 2016) both warn about this case: a brief move can trigger the order and the stock may later resume trading at its prior level. Had the price kept falling, the same stop would have saved money.

Choosing and maintaining a stop

Stop distance

Traders commonly set the distance as a fixed percentage (5% in Example 3) or from the stock's recent volatility; neither method comes from a regulator. A tight stop is hit more often by ordinary swings, as in Example 3; a wide one allows a larger loss per share. The distance also sets position size: dollars risked divided by the loss per share at the stop, so $300 / ($60 − $57) = 100 shares. The position size calculator runs the same arithmetic for other distances, and a gap can still make the real loss larger, as Example 2 shows.

Good-til-canceled stops

The Investor.gov order types bulletin says a GTC order lasts until executed or canceled, with a time limit that differs by firm. FINRA's order-qualifier page says that limit is often many months; Regulatory Notice 16-19 gives 90 days, with notice before expiry, as one limit firms might adopt. An expired stop protects nothing.

Frequently asked questions

Can a stop order be used on a short position?

Yes. Per Investor.gov, a buy stop is entered above the current price and is generally used to limit a loss or protect a profit on a stock sold short. It becomes a market order when the price rises to the stop, so gap risk applies in reverse.

Do all exchanges accept stop orders?

No. The SEC staff memorandum cites December 2015 filings by NYSE and NYSE MKT that removed stop orders from their rule books. That does not end stop orders for investors: the memorandum says the vast majority were held by broker-dealers, which send the order to the market once it is triggered. Whether a firm accepts them at all is its own choice under Rule 5350.

Does a stop-limit order change when a stock pays a dividend?

It can. FINRA's order-qualifier page says that, because a stock's price may fall by the dividend amount on the ex-dividend date, firms reduce the limit price on open limit and stop-limit orders by about the upcoming dividend. A "do not reduce" instruction keeps the original price, so check the firm's order terms before an ex-dividend date.

What happens to a stop placed as a Day order?

Investor.gov says orders are Day orders unless another time frame is specified, and an unexecuted Day order generally cancels at the end of regular trading hours, without carrying to the extended session or the next day. A stop meant to last beyond one session needs a different time-in-force setting, such as GTC.

Do regulators recommend stop orders?

They neither recommend nor ban them. Regulatory Notice 16-19 says stop orders may be a useful tool for investors who cannot regularly monitor prices, but are not without risks, and it asks firms to disclose those risks prominently. It also suggests firms consider making stop-limit orders the default type of stop order.

A checklist before placing a stop

Confirm the firm offers the order type and read how it decides the stop price has been reached (last sale, quotation, or round-lot print).
Decide whether a price guarantee or an execution guarantee matters more: stop-market, stop-limit, or a trailing version of either.
Choose the distance with the stock's usual swings in mind, and size the position from the loss at that distance. Allow for the gap risk in Example 2.
Check what the firm does in extended hours, near the open and close, and with GTC expiry or dividend adjustments.