What Slippage Costs a Trade and How to Limit It

Slippage is the difference between the price you expect when you submit an order and the average price at which it fills. It comes from the bid-ask spread, from thin quantities at the best prices, from price movement while the order is in transit, and from gaps between trading sessions. Order types can limit it, but each one gives up something else, usually certainty of getting filled.

Key takeaways

In the hypothetical below, a 5,000-share market buy at a $50.00 midpoint costs $305, or 12.2 basis points; two-thirds of that comes from walking past the best offer, not from the spread.
A limit order removes the price surprise but not the cost: in the same example, 2,500 shares go unbought and a later price rise makes the total shortfall larger.
A stop order becomes a market order when triggered, so it can fill far from the stop price; a stop-limit order caps the price but may not fill at all.
A cost of 2 basis points per trade looks trivial, yet 104 full-size trades a year remove about 2.1% of the account.

What slippage measures

Slippage needs a reference price, because "expected" is vague. The most common reference is the arrival price, the midpoint of the best bid and best offer at the moment the order is sent. The gap between the average fill and that price is the cost, in dollars or in basis points (bps), where one basis point is 0.01%.

Slippage (bps) = side × (average fill price − arrival price) ÷ arrival price × 10,000

side = +1 for a buy, −1 for a sell
average fill price = total dollars paid or received ÷ total shares filled
arrival price = midpoint of best bid and best offer when the order was sent

A positive result is a cost. A negative one is positive slippage, for instance when the quote moves your way in transit; it comes from the same mechanics and is not a reliable edge.

The wider measure is implementation shortfall: the gap between a paper trade at the arrival price and the real one, including fees and the price move on shares that never filled. Very large orders also push the price itself, an effect usually called market impact, which grows with size and is measured separately.

A market buy that walks a thin book

Illustrative example (hypothetical numbers, not a real quote). A stock shows a best bid of $49.98 and a best offer of $50.02, so the arrival midpoint is $50.00 and the spread is 4 cents. A trader sends a market order to buy 5,000 shares. The offers on the book at that instant are:

Offer price	Shares available	Shares filled	Dollars paid
$50.02	1,000	1,000	$50,020
$50.04	1,500	1,500	$75,060
$50.07	1,500	1,500	$75,105
$50.12	2,000	1,000	$50,120
Total		5,000	$250,305

The average fill is $250,305 ÷ 5,000 = $50.061. Against the $50.00 arrival price that is $0.061 per share, or $305 in total, and 0.061 ÷ 50.00 × 10,000 = 12.2 bps. Crossing from the midpoint to the best offer accounts for $0.02 × 5,000 = $100 (4.0 bps); the extra depth consumed beyond $50.02 accounts for the remaining $205 (8.2 bps).

The quote screen suggested a cost of half the 4-cent spread, 2 cents or 4 bps. The order paid roughly three times that because it was larger than the 1,000 shares displayed at the best price. The SEC's investor bulletin on order types describes this: parts of a large market order may execute at different prices due to a lack of liquidity at one price, and a market order's price often deviates from the last-traded price or the real-time quote (SEC Investor.gov, Understanding Order Types).

The same trade as a limit order

Suppose the trader instead places a buy limit order for 5,000 shares at $50.04. It can fill only at $50.04 or lower, so it takes 1,000 shares at $50.02 and 1,500 at $50.04, an average of $50.032 on 2,500 shares: $80 of slippage, or 6.4 bps. The other 2,500 shares remain unfilled at the limit.

Now the price rises and the trader gives up with the offer at $50.30. Against the $50.00 paper trade, the missed move costs $0.30 × 2,500 = $750. Total shortfall: $80 + $750 = $830 on a $250,000 order, or 33.2 bps, against 12.2 bps for the market order. Had the price drifted down instead, the resting $50.04 bid would have filled for a total of $180, or 7.2 bps. A limit order moves the cost from the fill price to the fill risk; it does not delete it.

Where slippage comes from

Five mechanisms account for most of it, and they stack.

Spread. A market order buys at the offer and sells at the bid, so it pays about half the quoted spread relative to the midpoint. Spreads tend to widen when markets move fast.
Depth. Only so many shares sit at each price. Once an order is bigger than the quantity at the best price it takes the next level, as in the table above.
Speed and latency. Between the moment you see a quote and the moment your order reaches the venue, the quote can change. FINRA notes that quotes may be delayed and that in highly volatile markets millions of shares can trade in microseconds (FINRA, Order Types).
Gaps. A gap is a price jump with no trades in between, typical at the open or after news outside regular hours. FINRA warns that for orders placed outside regular trading hours, news can significantly move the price when the market opens again.
Order size relative to the market. The bigger the order compared with what is displayed and what typically trades, the further it reaches into the book, so 100 shares and 100,000 shares do not get the same average price.

What the rules do and do not promise

Two rules are often misread as a price guarantee. FINRA's best-execution rule sets a duty of reasonable diligence in how a broker handles the order, not a promise of a particular price (FINRA Rule 5310). SEC Rule 611 requires trading centers to maintain policies designed to prevent trade-throughs, meaning regular-hours trades at a price worse than a protected quotation, subject to exceptions such as intermarket sweep orders (17 CFR 242.611). The SEC's definitions limit protected quotations to the best automated bid and offer of each exchange and of FINRA (17 CFR 242.600(b)). The orders queued behind those top quotes are not protected, so once the protected quotes are filled, the rest of a large order can execute at worse prices.

How order types limit it

Each order type chooses which risk to keep.

Order type	What it controls	What it gives up
Market	Speed: generally executes immediately	Price: the fill can differ from the quote you saw
Limit	Price: fills at the limit or better	Certainty: it may fill partly or not at all
Stop	Trigger: activates at the stop price	Price: it becomes a market order, so the fill can be far from the stop
Stop-limit	Trigger and a worst price	Certainty: if the price moves away from the limit it may not execute

The SEC's bulletin on stop orders adds two points the table cannot show. The stop price is a trigger, not a guaranteed execution price, and the resulting market order can deviate significantly from it. And brokerage firms differ both in which of these orders they offer and in how they decide that a stop price has been reached (SEC Investor.gov, Stop, Stop-Limit, and Trailing Stop Orders, updated August 18, 2026).

Tactics that work with the order type

Size orders to the displayed depth, or send them in slices; each slice walks less, but later slices face whatever the market does in between.
Use a limit price a few cents beyond the offer when a buy matters more than the last cent; it fills like a market order in normal conditions but cannot walk far.
Avoid market orders at the open, around scheduled releases, or when a quote looks stale; those are the moments when quotes and depth change fastest.

Small slippage, large annual drag

Illustrative example (hypothetical): a $50,000 account is fully reinvested on each trade, and every trade, buy or sell, costs the same slippage. The drag is roughly slippage in bps × number of trades ÷ 10,000.

Slippage per trade	Trades per year	Drag on the account	Dollar cost on $50,000
2 bps	24 (12 round trips)	0.48%	$240
2 bps	104 (52 round trips)	2.08%	$1,040
5 bps	24	1.20%	$600
5 bps	104	5.20%	$2,600

Compounding makes the true figure slightly lower (2.06% instead of 2.08% for 104 trades at 2 bps). Weekly round trips at 5 bps cost 5.2% of the account a year before commissions, taxes or losing trades.

Frequently asked questions

Does best execution mean I am guaranteed the quoted price?

No. FINRA Rule 5310 requires a broker to use reasonable diligence to find the best market so the price is as favorable as possible under prevailing market conditions, weighing factors such as the character of the market, the size and type of the transaction and the terms of the order. A market order for more shares than are displayed at the best price can still fill at several prices.

Why can a stop-loss fill far below the stop price?

Because a triggered stop order becomes a market order. Illustrative example (hypothetical): a sell stop at $48.00 on 200 shares, and news after the close makes the stock open at $45.50. Depending on the broker's trigger rules, the stop triggers at the open and the market order fills near $45.50, about $2.50 × 200 = $500 below the stop price. A stop-limit with a $47.80 limit would not sell at $45.50; unless the price climbed back to $47.80, the position would stay open.

Is slippage the same as price impact on a decentralized exchange?

Not exactly. Uniswap's documentation describes price impact as the price shift the swap itself causes against the pool's liquidity, which the interface estimates before you confirm. Slippage is a further price change while the transaction is pending, and a slippage tolerance sets the margin accepted beyond price impact; if the execution price falls outside it, the transaction fails (Uniswap documentation, Understanding Swaps). A tight tolerance works like a limit price; the protocol is named only to illustrate the mechanism.

Can I see how my broker's executions compare with others?

Partly. SEC Rule 605 requires market centers, and brokers that introduce or carry 100,000 or more customer accounts, to publish monthly execution-quality reports on exchange-listed (NMS) stocks, with statistics such as average effective spread and price improvement, grouped by security, order type and size (17 CFR 242.605). The SEC amended the rule in 2024; after one extension, compliance with the amendments began on August 1, 2026, and the first reports in the new format, covering August 2026, were due by the end of September 2026 (Federal Register, October 2, 2025). The reports describe averages across many orders, not your own fills.

Do commissions count as slippage?

No. A commission is a stated charge; slippage is the gap between the reference price and the fill. Track them in separate columns to see which costs more.

A routine for tracking slippage

Export each order's side, submission time, fill times, fill prices and share counts, at the broker's full price precision; rounding to two decimals hides fractions of a cent.
Record the arrival midpoint for each order at submission and compute the formula above for every filled order.
Group by market versus limit orders, order size, and time of day (open, midday, close, around releases). Use a single time zone throughout.
For limit orders, log the fill rate and add the price move on unfilled shares to get the implementation shortfall.
Re-run any backtest with slippage from the upper end of your measured range, not the average, and change one execution variable (size, order type, timing) at a time.