Direct Answer
Slippage is the difference between the price at which an order was expected to execute, such as the last quote when it was sent, and the price it actually received. It is the practical shortfall between a planned and a realized fill. Positive slippage is a cost; negative slippage means a better fill than expected.
Slippage: Formula, Meaning, Signals, Examples and How to Use It
How Is Slippage Calculated?
Slippage is the difference between the price at which an order was expected to execute, such as the last quote when it was sent, and the price it actually received. It is the practical shortfall between a planned and a realized fill.
Formula: Slippage = side x (Executed Price - Expected Price) / Expected Price, with side = +1 for buys and -1 for sells; positive means a cost
Inputs:
- Executed (average fill) price
- Expected price (quote or last price when the order was sent)
- Order side
Worked example. A buy order expected at 100.00 that fills at 100.08 has a slippage of 0.08%. The inputs are illustrative numbers, not market data.
Reading it. Positive slippage is a cost; negative slippage means a better fill than expected. Larger orders, fast markets and thin books produce more slippage, and it is the figure to include when backtesting or estimating the cost of a strategy.
Limits. 'Expected price' is not universal: the last trade, the quote or the arrival midpoint give different answers. It mixes market movement and the order's own impact, and benchmark-specific versions (arrival, VWAP, TWAP) give different readings on the same fills.
What is Slippage?
Slippage is the difference between the price at which an order was expected to execute, such as the last quote when it was sent, and the price it actually received. It is the practical shortfall between a planned and a realized fill.
How to use Slippage
Positive slippage is a cost; negative slippage means a better fill than expected. Larger orders, fast markets and thin books produce more slippage, and it is the figure to include when backtesting or estimating the cost of a strategy. A reading alone is never a buy or sell signal; it needs context from price structure, volume, volatility and the broader market regime.
Strengths
- Signing by side lets buys and sells be averaged on a single scale where a positive value always means cost.
- It is expressed as a fraction of the expected price, so costs for stocks at different price levels are comparable.
- Reproducible when the formula and data convention are fixed.
Weaknesses and limitations
- Average execution price weights fills by size, so a few large fills at a bad price dominate even if most fills were good.
- Fees, rebates and taxes are normally left out, so total trading cost is higher or lower than the slippage figure depending on venue and plan.
- Correlated indicators can create false confidence by repeating the same underlying information.
Editorial and risk note
This page is educational content, not individualized investment advice. It should not imply guaranteed prediction, accuracy or outperformance.
Frequently Asked Questions
Is Slippage a buy or sell signal?
No. Positive slippage is a cost; negative slippage means a better fill than expected. 'Expected price' is not universal: the last trade, the quote or the arrival midpoint give different answers. A trade built on it still needs a trigger, an invalidation rule, a position size and realistic execution assumptions.
What is the best setting for Slippage?
Slippage takes these inputs: executed (average fill) price; expected price (quote or last price when the order was sent); order side. There is no universal best setting for the tunable ones, so test them across instruments, regimes and out-of-sample periods and favor stable parameter regions over one historical winner.
Can Slippage be used by itself?
'Expected price' is not universal: the last trade, the quote or the arrival midpoint give different answers. It mixes market movement and the order's own impact, and benchmark-specific versions (arrival, VWAP, TWAP) give different readings on the same fills. For that reason it is read next to measures of direction, participation, valuation, liquidity and risk, not alone.
Does Slippage work on every timeframe?
The calculation (Slippage = side x (Executed Price - Expected Price) / Expected Price, with side = +1 for buys and -1 for sells; positive means a cost) can be run on any bar size, but behavior is not portable: a reading on a five-minute chart describes a very different market window from the same reading on a daily chart. Validate the exact timeframe before relying on it.
Why does Slippage give false signals?
Average execution price weights fills by size, so a few large fills at a bad price dominate even if most fills were good. Fees, rebates and taxes are normally left out, so total trading cost is higher or lower than the slippage figure depending on venue and plan. Lag, noise and regime changes add to this, because market participants react to new information after the reading is calculated.
How should Slippage be backtested?
Rebuild Slippage from executed (average fill) price using point-in-time data, write the rules before testing, include delisted securities where relevant, model realistic fills and costs, reserve a validation sample and compare with a simpler baseline.