Slippage: The Gap Between the Price You Saw and the Price You Got

Slippage is the difference between the price you expected when you hit the button and the price you actually filled at — and on fast or thin names it can quietly eat an edge. This page explains what causes it, where it bites hardest, and how order type and venue choice keep it small, using the same execution mechanics covered in our free handbook. Research and education only — not financial advice.

The short answer

Slippage is the difference between the price you expected to trade at and the price you actually got. It happens because the market moves — or the order book thins out — in the fraction of a second between your decision and your fill, and it is almost always a cost, not a gift. The price glowing on your screen is the last trade or a mid-quote; it is not a promise that you can transact there.

Why slippage happens

Three forces produce it, and they often stack:

The spread. Every quote has a bid and an ask. A market order to buy takes the ask; a market order to sell hits the bid. If you mentally anchored to the mid-price, you have already slipped by half the spread before anything moves.
Speed. Quotes update many times a second. When a stock or option is running, the ask you saw can be gone by the time your order reaches the exchange, and you fill at the next available price up the ladder.
Depth. The book only holds so many shares or contracts at each price. If your order is larger than what's resting at the top, it "walks the book," filling progressively worse at each deeper level.

A worked example

Say XYZ last printed $50.00 and you send a market order for 2,000 shares. The offer side of the book looks like this:

Price	Shares offered	Yours filled
$50.00	300	300
$50.03	500	500
$50.08	2,000	1,200

Your 2,000 shares fill at a weighted average of about $50.06, not the $50.00 you saw. That six-cent gap is roughly $110 of slippage on a single ticket — paid to the structure of the market before your thesis has done anything. Read that number as a percentage of your intended risk, not in isolation: a risk-reward calculator will show how a few cents of slippage on entry and exit shrinks a 2:1 setup toward 1.7:1.

Rule of thumb. Measure expected slippage against the spread and your target. On a penny-wide, heavily traded name it's noise. On a name where the spread is already several percent of the price, a market order can hand away a chunk of the trade before it starts.

Where it bites hardest

Thin stocks. Low-volume names have shallow books. There may be only a few hundred shares near the top of the market, so any real size walks the book immediately. The advertised price is real for 100 shares and fiction for 5,000.

Options. This is where beginners get hurt most. Option quotes are per share but each contract covers 100 shares, and out-of-the-way strikes trade rarely, so market makers post wide. A contract quoted $0.40 bid / $0.55 ask means a market order to buy pays $0.55 and an instant exit returns $0.40 — you are down roughly 27% on the spread alone, before the underlying moves. Our options handbook walks through this on a real, timestamped contract.

Fast markets. Around earnings, an economic print, or a scalp into a momentum spike, quotes tear. A market order sent into that can fill dramatically worse than the last tick — and 0DTE options, with their violent gamma-driven moves, are the extreme case.

Stops slip too. A standard stop-loss is not a limit — when it triggers, it becomes a market order and takes whatever is available. In a gap-down, a fast flush, or after a halt reopens, that fill can be far below your stop level. This is exactly why resting a tight market-style stop on a thin, sub-$1 option premium is dangerous: the exit you were counting on may not exist at your price when you need it.

How to limit slippage

You cannot delete slippage, but you can control most of it with a handful of habits:

Use limit orders. A limit order names the worst price you'll accept and refuses to fill beyond it. You trade certainty of execution for certainty of price — usually a good trade when the price matters more than the millisecond. Start a limit near the mid and nudge it a cent toward the ask if it doesn't fill.
Trade liquid names and strikes. High volume and deep open interest mean tight quotes and clean exits. A slightly worse-looking strike with a crowd around it usually beats a "cheaper" ghost-town strike whose spread eats the edge.
Size to the book. Keep your order small relative to what's resting and to a strike's open interest, so you aren't the one walking the ladder. Splitting a large order into pieces also reduces impact.
Mind the clock. The first and last minutes of the session, and the seconds around a scheduled release, carry the widest, fastest quotes. Unless volatility is your setup, waiting for the book to settle costs you less.
Use stop-limits where it fits. A stop-limit caps how far your exit can slip — at the cost of possibly not filling at all if price races past the limit. That trade-off is a judgment call, not a free lunch.

How a research desk treats slippage

At ClaudeQuantAlgo, execution cost is a gate, not a footnote. Before an idea becomes a trigger-based card, it passes a liquidity screen: is the spread tight as a percentage of price, is there real volume and open interest, and is a realistic position small enough to exit cleanly? A card that clears those checks then defines an explicit trigger, TP1/TP2, stop, and time-stop — the point being an entry and an exit you can actually get at a fair price. You can watch how those cards behave, wins and losses alike, on our public, timestamped paper record (a model desk, no real money), and see the screening logic in the signals overview. The published blind backtest of the raw scanner — 161 simulated trades, 46.6% hypothetical win rate, 0.82 profit factor — is exactly the kind of number that assumes clean fills; real slippage is one reason live results and hypothetical ones diverge, and why order discipline is part of every card.

Common questions

What is slippage in trading?

Slippage is the difference between the price you expected to trade at and the price you actually filled at. The number on your screen is the last trade or a mid-quote, not a guarantee. Between your decision and your fill, the market can move or the top of the order book can empty, so you fill at a worse price — usually by the spread or more.

Why do market orders slip more than limit orders?

A market order accepts any available price to guarantee a fill, so it takes the ask when buying and the bid when selling, and it walks deeper into the book if it's larger than what's resting at the top. A limit order names the worst price you'll accept and refuses to fill past it, trading execution certainty for price certainty.

Why is slippage worse on options and thin stocks?

Thin names and out-of-the-way option strikes have shallow order books and wide bid-ask spreads because few participants compete to quote them. A wide spread means you start each trade well behind, and shallow depth means any real size fills at progressively worse prices. Fast-moving contracts like 0DTE options compound the problem.

Can a stop-loss experience slippage?

Yes. A standard stop-loss becomes a market order the moment it triggers, so in a gap, a fast flush, or a halt reopen it can fill far below your stop level. A stop-limit caps how far the exit can slip but may not fill at all if price races past the limit — a trade-off you choose deliberately, not a free fix.

See the process with your own eyes. The desk posts trigger-based cards to a public, timestamped record — losses included — and published the backtest where its own raw scanner loses. The scoreboard is free to watch. Join the floor →

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Last updated 2026-07-11 · ClaudeQuantAlgo Research Desk · research and education only.

Disclosures. ClaudeQuantAlgo is a research and education community. Nothing on this page constitutes financial, investment, legal, or tax advice, or a recommendation to buy or sell any security or derivative. No profit promises are made, ever — trading stocks, options, and forex involves substantial risk of loss; options positions can lose 100% of their value. The public scoreboard reflects a model ("paper") desk — no real money. Past performance — real, paper, or simulated — never guarantees future results. Hypothetical and simulated results have inherent limitations and no representation is made that any account will or is likely to achieve similar profits or losses. ClaudeQuantAlgo is not a registered investment adviser or broker-dealer. You are solely responsible for your own trading decisions. Never risk money you cannot afford to lose.